Synthesis, solvent interactions and computational study of monocarbohydrazones

Chemical Papers

https://doi.org/10.1007/s11696-020-01106-4

ORIGINAL PAPER

Synthesis, solvent interactions and computational study

of monocarbohydrazones

Gorana S. Mrdjan¹· Borko M. Matijević¹· Gyöngyi Gy. Vastag¹· Aleksandra R. Božić²·

Aleksandar D. Marinković³· Miloš K. Milčić⁴· Ivana N. Stojiljković⁵

Received: 27 September 2019 / Accepted: 14 February 2020

Abstract

Carbohydrazones are compounds that are increasingly studied due to their wide potential biological activity. Monocarbo-

hydrazones (mCHs), as one of the carbohydrazone derivatives, so far have been poorly investigated. For a more detailed

study, in this paper, eighteen compounds of monocarbohydrazones (eight known and ten newly synthesized derivatives) were

synthesized and characterized using NMR and IR spectroscopy. As carbohydrazones show E/Z isomerization caused by the

presence of the imino group, some of the synthesized mCHs are in the form of a mixture of these two isomers. The efects

of specifc and nonspecifc solvent–solute interactions on the UV absorption maxima shifts were evaluated using linear free

energy relationships principles, i.e., using Kamlet–Taft’s and Catalan’s models. For more information about interactions

between dissolved substance and the surrounding medium, correlations have been made with Hansen’s solubility parameters.

The infuence of the structure on the spectral behavior of the compounds tested was interpreted using Hammett’s equation.

Experimentally obtained physicochemical properties of mCHs were compared to and confrmed with computational methods

that included TD-DFT calculations and MP2 geometry optimizations.

Electronic supplementary material The online version of this

article (https://doi.org/10.1007/s11696-020-01106-4) contains

supplementary material, which is available to authorized users.

* Gorana S. Mrdjan

gorana.mrdjan@dh.uns.ac.rs

1

Department of Chemistry, Biochemistry and Environmental

Protection, Faculty of Sciences, University of Novi Sad, Trg

Dositeja Obradovića 3, Novi Sad 21000, Serbia

2

Belgrade Polytechnic, Brankova 17, Belgrade 11000, Serbia

3

Faculty of Technology and Metallurgy, University

of Belgrade, Karnegijeva 4, Belgrade 11000, Serbia

4

Faculty of Chemistry, University of Belgrade, Studentski trg

12-16, Belgrade 11000, Serbia

5

Faculty of Forestry, University of Belgrade, Kneza Viseslava

1, Belgrade 11000, Serbia

Vol.:(0123456789)

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Chemical Papers

Graphic abstract

Keywords Monocarbohydrazones · Solvent interactions · Substituent efects · Molecular geometry optimization · TDF

calculations

Considering their wide application, mCHs have been

slightly tested and all reports lack detailed structural and

theoretical study. Because of that, in this work, we report the

synthesis and characterization of eighteen mCHs, of which

eight are already known and ten are newly synthesized. All

compounds were characterized using NMR, IR, UV–Vis

spectroscopy and elemental analysis. Previous studies have

shown that carbohydrazones might exist in keto or enol

tautomeric form and adopt E or Z confguration around the

imino group (Zelenin et al. 1999). In this work, some of the

synthesized compounds were presented as a mixture of both

isomers, and their stereochemistry was proven with the use

of 2D homonuclear (NOESY) and heteronuclear (HSQC and

HMBC) NMR techniques.

Introduction

Carbohydrazide represents a hydrazine derivative of car-

bonic acid that possesses two reactive hydrazine groups

capable of condensation with one or two carbonyl com-

pounds to produce mono- and bis-carbohydrazones, respec-

tively (Zhang et al. 2006). Due to the wide biological and

clinical activity, this group of compounds is becoming an

area of great interest to scientists. Previous studies have

shown that they possess anticancer, anti-tumor, antioxidant,

anti-viral, anti-infammatory, antimicrobial and anti-diabetic

activity (Bacchi et al. 1999; Rollas and Küçükgüzel 2007;

Gangarapu et al. 2014 ; Kajal et al. 2014; Božić et al. 2016;

Božić et al. 2017a ). In addition t o the biological activity,

carbohydrazones have also proved to be good oxygen reduc-

tion catalysts (Kamyabi et al. 2017) and carbonic anhydrase

inhibitors (Iqbal et al. 2017 ). Also, for example, the most

structurally characterized monocarbohydrazones (mCHs)—

salycilaldehydecarbohydrazone—are known as an aluminum

detector in water (Sánchez Rojas et al. 1994). Furthermore,

due to their reactivity, they can easily react with various

transition metals and build complexes (Babahan et al. 2011;

Shebl and Khalil 2015 ; Dragancea et al. 2016; Gholivand

et al. 2016; Wang et al. 2017). Some of the complexes made

with Cd(II), for example, show better antimicrobial activity

than the ligands themselves (Montazerozohori et al. 2014).

The UV data were analyzed using LSER and LFER

models, respectively, to evaluate the infuence of solvent/

solute interactions and substituent efects on the spectra

of the investigated compounds. The efect of solvent was

interpreted by two most commonly used models, Cata-

lan’s and Kamlet–Taft’s. Also, for additional information

on the interactions between the solvent and the dissolved

substance, correlations with Hansen’s solubility parameters

have been made. The infuence of the type of substituent,

as well as their position, on the benzene ring was charac-

terized by Hammett’s equation. Experimentally obtained

physicochemical properties of monocarbohydrazones were

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compared to and confrmed with computational methods that

included TD-DFT calculations and MP2 geometry optimiza-

tions. Charge-transfer distance (DCT), amount of transferred

charge (QCT) and Tozer’s Λ diagnostic index were evaluated

according to the method proposed by Le Bahers. Orbitals

with the highest contribution to the nature of the frst excited

state were localized with the NBO localization procedure.

investigated compounds with time-dependant (TD) density

functional theory (DFT) method using long-range cor-

rected CAM-B3LYP functional (Yanai et al. 2004) and

6-311G(d,p) basis set in gas phase. The nature of investi-

gated excitations was further confrmed by calculating quali-

tative charge-transfer indices including the charge-transfer

distance (D_CT) and amount of transferred charge (Q_CT). The

ground-state (DFT) and excited-state (TD-DFT) electron

densities were calculated at MP2/6-311G(d,p) optimized

geometries with the CAM-B3LYP/6-311G(d,p) functional/

basis set. The charge-transfer indices were calculated from

obtained ground- and excited-state electron densities accord-

ing to the method proposed by Le Bahers et al. (2011) with

CT program (Jacquemin et al. 2012).

Experimental

Materials

All chemicals used for synthesis were from Sigma-Aldrich

and with the quality of the synthesis. They were used with-

out prior purifcation. Solvents used for recording the UV

spectra were also from Sigma-Aldrich and with high degree

of purity and quality for spectrophotometric measurements:

methanol, ethanol, n-propanol, n-butanol, n-pentanol, i-pro-

panol, i-butanol, t-butanol, acetic acid, acetonitrile (AcN),

dimethyl sulfoxide (DMSO), N,N-dimethylformamide

(DMF), dichloromethane (DCM), chloroform, ethyl acetate

(EtAc), tetrahydrofuran (THF), 1,4-dioxane and diethyl

ether.

Theoretical absorption spectra are calculated starting

from MP2/6-311G(d,p) optimized geometries in two dif-

ferent solvents: DMSO and methanol with the TD-DFT

method. These TD-DFT calculations were done with B3LYP

functional (Becke 1993) and 6-311G(d,p) basis set. Solvent

efects have been simulated with the standard static isoden-

sity surface-polarized continuum model (IPCM) (Wiggins

et al. 2009).

In order to visualize the nature of the frst excited state,

the orbitals with the highest contribution to this excited state

were localized with NBO localization procedure (Reed and

Weinhold 1985) using the NBO 3.1 program (Glendening

et al. 2003 ).

Melting points of tested compounds were determined

with Kofer’s device. The elemental analysis was performed

using a Vario El III elemental analyzer. IR spectra were

recorded on a Nicolet Nexus 670 FTIR (Thermo Scientifc)

spectrophotometer, in the range of 400–4000 cm⁻¹using the

KBr pellet technique. NMR spectral assignments and struc-

tural parameters were obtained by the combined use of 1D

(¹H and ¹³C) and 2D (NOESY, ¹H–¹³C HSQC and ¹H–¹³C

HMBC) spectroscopy. The NMR spectra were performed on

Bruker Avance 400 equipped with a broadband direct probe.

Chemical shifts are given on δ scale relative to tetramethylsi-

lane (TMS) as an internal standard for ¹H and ¹³C. Coupling

constants (J) were expressed in Hz. Abbreviations used for

NMR spectra are: s, singlet; dd, doublet of doublets; t, tri-

plet; m, multiplet. UV absorption spectra were recorded by

using a Shimadzu UV-1800 spectrophotometer in 1.00-cm

cells at 25 0.1 °C at concentration of 4×10⁻⁵mol dm⁻³.

Geometries of Z and E isomers of all investigated mole-

cules were optimized in gas phase by the MP2 method using

the 6-311G(d,p) basis set. To fnd the global minimum on

the potential energy surface, multiple geometry optimiza-

tions were performed for every compound starting from

diferent initial geometries and minimizing the energy con-

cerning all geometrical parameters. The nature of the low-

est energy minimum was further confrmed with frequency

calculations; no negative frequencies were found.

All quantum c hemical calculations were carried out using

the Gaussian 09 program (Frisch et al. 2016).

Synthesis and results of characterization

of N‑benzylidene‑carbohydrazones

The basic compound for the synthesis of mCHs, carbohy-

drazide (dhO), was prepared according to a well-known pro-

cedure (Zhang et al. 2006). The purity of the synthesized

dhO was checked by NMR spectroscopy, elemental analysis

and melting point (M.p. 153 °C, M.p. Lit. data 153–154 °C)

(Kurzer and Wilkinson 1970).

Monocarbohydrazones (1–18) were synthesized by the

reaction between dhO (1 mmol) and appropriate benzalde-

hydes (0.5 mmol) in two diferent solvents, depending on the

aggregate state of aldehydes that were added. The general

procedure for the synthesis of mCHS is shown in Scheme 1.

Compounds 3, 4, 8–11, 15 and 17 were obtained by

reaction of the carbohydrazide dissolved in ethanol [30 ml,

(70%)] and the corresponding benzaldehyde also dissolved

in ethanol (10 ml). The reaction was carried out under refux

for 2.5 h. A drop of glacial acetic acid was added as a cata-

lyst at the beginning of the reaction. Compounds 1, 2, 5–7,

12–14, 16 and 18 were prepared in an analogous manner

(molar ratio) applied within the previously shown proce-

dure, using water as a dissolving solvent (10 ml) at room

In order to estimate a nature of excitations [charge-

transfer (CT) or local excitations (LE)], Tozer’s Λ diag-

nostic index (Peach et al. 2008) was calculated for all the

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Scheme 1 Reaction of synthesis of monocarbohydrazones

1

temperature with one drop of glacial acetic acid. The reac-

tion mixture was stirred for 0.5 h. After synthesis, all com-

pounds were collected by fltration and washed successively

with cold alcohol and diethyl ether, dried and recrystallized

from a suitable solvent. Compounds 1 and 2 (Božić et al.

2017b), 4 and 13 (Okawara et al. 2006), 7, 15 and 18 (War-

kentin et al. 1977) and 10 (Zelenin et al. 1999) are known

compounds that have been previously synthesized. All these

compounds are synthesized by our procedures, and their

purity was verifed through melting point, elemental analy-

sis, IR and NMR spectroscopy. Compounds 7, 15 and 18 are

known, but they are not characterized. Obtained results for

substances 1, 2, 4, 10 and 13 are in agreement with the lit-

erature data. A list of synthesized compounds with numera-

tion of the atoms of interest is given in Scheme 1.

157.59 (C8). Lit. data: H NMR (100 MHz, DMSO-d₆,

δ (ppm)): 4.10 (s, 2H, H2–N4), 7.2–7.5 (m, 2H, H–C2,

H–C6), 7.60–7.80 (m, 3H, H–C3, H–C4, H–C5), 7.92 (s,

1H, H–N3), 8.10 (s, 1H, H–C7), 10.50 (s, 1H, H–N2). ¹³

C

NMR (126 MHz, DMSO-d₆, δ (ppm): 125.49 (C3=C5);

128.68 (C2=C6); 131.61 (C4); 134.85 (C1); 140.76 (C7);

157.20 (C8) (Božić et al. 2017b).

2‑Hydroxybenzaldehyde carbohydrazone (2)

White substance, recrystallized from ethanol. Yield: 76%.

m.p. 191 °C. Elemental analysis: Calculated for C₈H₁₁N₄O₂

(Mw= 194.37 gmol⁻¹): C, 49.48; H, 5.19; N, 28.85; O,

16.48%. Found: C, 49.11; H, 5.12; N, 28.78; O, 16.99%.

IR (KBr, cm⁻¹) ν_max: 3353 (OH), 3283 s (NH₂), 3098 m

(NH), 1681 s (C=O), 1633 m (C=N), 1556 s and 1491 m

(C=Carom.), 1169 m-s (Ar–OH); 739 m (C–H band

Benzaldehydecarbohydrazone (1)

1

(ortho)). H NMR (400 MHz, DMSO-d₆, δ (ppm)): 4.16

White substance, recrystallized from ethanol. Yield: 81%.

m.p. 172–174 °C (literary m.p. 173 °C). Elemental analy-

sis: calculated for C₈H₁₀N₄O (Mw= 178.37 gmol⁻¹): C,

53.92; H, 5.66; N, 31.44; O, 8.98%. Found: C, 53.81; H,

5.02; N, 30.87; O, 10.30%. IR (KBr, cm⁻¹) ν_max: 3319 m

(NH₂), 3092w (NH), 1682 s (C=O), 1601 m (C=N), 1551 s

and 1448 m (C=Carom.), 753 m and 697 m (C–H band

(mono)). ¹H NMR (400 MHz, DMSO-d₆, δ (ppm)): 4.05 (s,

2H, H2–N4), 7.73 (d, 2H, H–C2=H–C6, ³J_2,3=6.9 Hz=³

J_6,5=6.9 Hz), 7.32–7.40 (m, 3H, H–C3, H–C4, H–C5), 7.87

(s, 1H, H–N3), 8.01 (s, 1H, H–C7), 10.38 (s, 1H, H–N2).

¹³C NMR (126 MHz, DMSO-d₆, δ (ppm): 127.13 (C3=C5);

129.03 (C2=C6); 129.57 (C4); 135.13 (C1); 140.82 (C7);

(s, 2H, H2–N4), 6.79–6.89 (m, 2H, H–C5, H–C3), 7.18 (td,

1H, H–C4, ³J_4,5=7.7 Hz, ⁴J_4,6=1.4 Hz), 7.64 (s, 1H, H–C6),

7.92 (s, 1H, H–N3), 8.22 (s, 1H, H–C7), 10.08–10.73 (spm,

2H, OH, H–N2). ¹³C NMR (126 MHz, DMSO-d₆, δ (ppm)):

116.09 (C6), 119.22 (C4), 120.06 (C1), 127.86 (C3), 130.23

(C5), 140.22 (C7), 156.24 (C2), 157.92 (C8). Lit. data: ¹H

NMR (500 MHz, DMSO-d₆, δ (ppm): 4.16 (s, 2H, H2–N4),

6.79–6.89 (m, 2H, H–C5, H–C3), 7.18 (td, 1H, H–C4,

³J_4,5=7,7 Hz, ⁴J_4,6=1.4 Hz), 7.64 (s, 1H, H–C6), 7.92 (s,

1H, H–N3), 8.22 (s, 1H, H–C7), 10.08–10.73 (spm, 2H, OH,

H–N2). ¹³C NMR (126 MHz, DMSO-d₆, δ (ppm)): 116.09

(C6), 119.22 (C4), 120.06 (C1), 127.86 (C3), 130.23 (C5),

140.22 (C7), 156.24 (C2), 157.92 (C8) (Božić et al. 2017b).

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3‑Hydroxybenzaldehyde carbohydrazone (3)

8.73%. IR (KBr, cm⁻¹) ν_max: 3297 m (NH₂), 3090 m (NH),

1678 s (C=O), 1645 m (C=N), 1522 s and 1458 m (C=C

1

Yellow substance, recrystallized from ethanol. Yield: 58%.

m.p. 148 °C. Elemental analysis: Calculated for C₈H₁₁N₄O₂

(Mw= 194.37 gmol⁻¹): C, 49.48; H, 5.19; N, 28.85; O,

16.48%. Found: C, 48.96; H, 5.03; N, 28.66; O, 17.35%.

IR (KBr, cm⁻¹) ν_max: 3337 m (OH), 3304 s (NH₂), 3091 m

(NH), 1669 s (C=O), 1617 m (C=N), 1529 s and 1454 m

(C=C arom.), 1270 m-s (Ar–OH), 781 s and 686 s (C–H

arom.), 751 m (C–H band (ortho)). H NMR (400 MHz,

DMSO-d₆, δ (ppm)): 2.36 (s, 3H, CH3), 4.09 (s, 2H,

H2–N4), 7.16–7.29 (m, 3H, H–C5, H–C4, H–C3), 7.90 (s,

1H, H–C7), 7.96 (d, 1H, H–C6, ³J_6,5=7.3 Hz), 8.16 (s, 1H,

H–N3), 10.30 (s, 1H, H–N2). ¹³C NMR (126 MHz, DMSO-

d₆, δ (ppm)): 19.43 (CH3), 126.22 (C6), 126.44 (C1), 129.27

(C3), 131.04 (C4), 133.03 (C6), 136.26 (C2), 139.27 (C7),

157.52 (C8).

1

band (meta)). Ratio E:Z isomers (86:14). Isomer E: H

NMR (400 MHz, DMSO-d₆, δ (ppm)): 4.07 (s, 2H, H2–N4),

6.76 (d, 1H, H–C4, ³J_4,5=7.6 Hz), 7.11–7.23 (m, 3H, H–C2,

H–C5, H–C6), 7.78 (s, 1H, H–N3), 7.90 (s, 1H, H–C7), 9.51

(s, 1H, H–OH), 10.34 (s, 1H, H–N2). ¹³C NMR (126 MHz,

DMSO-d₆, δ (ppm)): 113.43 (C2), 116.80 (C4), 118.34 (C6),

130.01 (C5), 136.38 (C1), 141.04 (C7), 157.54 (C3), 157.97

(C8). Isomer Z: ¹H NMR (400 MHz, DMSO-d₆, δ (ppm)):

3‑Methylbenzaldehyde carbohydrazone (6)

White substance, recrystallized from ethanol. Yield: 63%.

m.p. 179–181 °C. Elemental analysis: Calculated for

C₉H₁₂N₄O (Mw= 192.38gmol⁻¹): C, 56.24; H, 6.29; N,

29.15; O, 8.32%. Found: C, 55.91; H, 6.42; N, 29.33; O,

8.34%. IR (KBr, cm⁻¹) ν_max: 3304 s (NH₂), 3083 m (NH),

1676 s (C=O), 1614 m (C=N), 1521 s (C=Carom.), 788 s

and 692 s (C–H band (meta)). ¹H NMR (400 MHz, DMSO-

d₆, δ (ppm)): 2.32 (s, 3H, CH3), 4.08 (s, 2H, H2–N4),

3

4.07 (s, 2H, H2–N4), 6.80 (d, 1H, H–C4, J_4,5= 7.9 Hz),

7.11–7.23 (m, 3H, H–C2, H–C5, H–C6), 7.82 (s, 1H,

H–N3), 8.09 (s, 1H, H–C7), 9.58 (s, 1H, H–OH), 10.63

(s, 1H, H–N2). ¹³C NMR (126 MHz, DMSO-d₆, δ (ppm)):

113.54 (C2), 117.16 (C4), 118.63 (C6), 130.12 (C5), 136.46

(C1), 152.53 (C7), 158.06 (C3), 162.47 (C8).

3

7.15 (d, 1H, H–C4, J_4,5= 7.6 Hz), 7.26 (t, 1H, H–C5,

³J_5,4=7.6 Hz), 7.48 (d, 1H, H–C6, ³J_6,5=7.6 Hz), 7.60 (s,

1H, H–C2), 7.82 (s, 1H, H–C7), 8.00 (s, 1H, H–N3), 10.36

(s, 1H, H–N2). ¹³C NMR (126 MHz, DMSO-d₆, δ (ppm)):

21.33 (CH3), 124.59 (C6), 127.39 (C5), 128.89 (C2), 130.22

(C4), 135.12 (C1), 138.22 (C3), 140.66 (C7), 157.57 (C8).

4‑Hydroxybenzaldehyde carbohydrazone (4)

White substance, recrystallized from methanol. Yield:

69%. m.p. 223–225 °C. Elemental analysis: Calculated

for C₈H₁₁N₄O₂(Mw= 194.37 gmol⁻¹): C, 49.48; H,

5.19; N, 28.85; O, 16.48%. Found: C, 49.27; H, 5.22; N,

28.89; O, 16.62%. IR (KBr, cm⁻¹) ν_max: 3430 m (OH),

3318 s (NH₂), 3069 m (NH), 1698 s (C=O), 1637 m

(C=N), 1518 s and 1442 m (C=Carom.), 1241 m-s

(Ar–OH); 824 m (C–H band (para)). ¹H NMR (400 MHz,

DMSO-d₆, δ (ppm)): 4.06 (s, 2H, H2–N4), 6.76 (d,

4‑Methylbenzaldehyde carbohydrazone (7)

White substance, recrystallized from methanol. Yield:

67%. m.p. 225–228 °C. Elemental analysis: Calculated for

C₉H₁₂N₄O (Mw= 192.38 gmol⁻¹): C, 56.24; H, 6.29; N,

29.15; O, 8.32%. Found: C, 56.39; H, 6.17; N, 29.12; O,

8.32%. IR (KBr, cm⁻¹) ν_max: 3341 m (NH₂), 3079 m (NH),

1668 s (C=O), 1610 m (C=N), 1509 s and1480m (C=C

3

2H, H–C5=H–C3 J_3,2= ³J_5,6= 8.6 Hz), 7.55 (d, 2H,

3

1

H–C6=H–C2, J_2,3= ³J_6,5= 8.6 Hz), 7.75 (s, 1H, H–C7),

arom.), 830 m (C–H band (para)). H NMR (400 MHz,

7.85 (s, 1H, H–N3), 9.77 (s, 1H, OH), 10.16 (s, 1H,H–N2).

¹³C NMR (126 MHz, DMSO-d₆, δ (ppm)): 115.88 (C3=C5),

126.26 (C1), 128.76 (C2=C6), 141.00 (C7), 157.75 (C8),

DMSO-d₆, δ (ppm)): 2.31 (s, 3H, CH3), 4.10 (s, 2H,

H2–N4), 7.19 (d, 2H, H–C5=H–C3 ³J_3,2= ³J_5,6= 7,9 Hz),

3

7.62 (d, 2H, H–C6=H–C2, J_2,3= ³J_6,5= 7.9 Hz), 7.82 (s,

158.98 (C4). Lit. data: H NMR (500 MHz, DMSO-d₆, δ

1H, H–C7), 7.98 (s, 1H, H–N3), 10.33 (s, 1H, H–N2). ¹³

C

1

(ppm): 4.04 (s, 2H, H2–N4), 6.74 (d, 2H, H–C5, H–C3),

7.53 (d, 2H, H–C6, H–C2), 7.73 (s, 1H, H–C7). ¹³C NMR

(126 MHz, DMSO-d₆, δ (ppm)): 115.00 (C3=C5), 125.00

(C1), 128.00 (C2=C6), 140.00 (C7), 157.00 (C8), 158.22

(C4) (Okawara et al. 2006).

NMR (126 MHz, DMSO-d₆, δ (ppm)): 21.41 (CH3), 127.10

(C3=C5), 129.62 (C2=C6), 132.51 (C1), 139.13 (C4),

140.74 (C7), 157.61 (C8) (Warkentin et al. 1977).

2‑Nitrobenzaldehyde carbohydrazone (8)

2‑Methylbenzaldehyde carbohydrazone (5)

Yellow substance, recrystallized from methanol. Yield: 72%.

m.p. 237 °C. Elemental analysis: Calculated for C₈H₉N₅O₃

(Mw= 223.44 gmol⁻¹): C, 43.05; H, 4.06; N, 31.38; O,

21.50%. Found: C, 42.87; H, 4.12; N, 30.97; O, 22.04%.

IR (KBr, cm⁻¹) ν_max: 3361 m (NH₂), 3088 m (NH), 1701 s

(C=O), 1615 m (C=N), 1528 s and 1344 s (NO), 1593 m

White substance, recrystallized from n-propanol. Yield:

61%. m.p. > 240 °C. Elemental analysis: Calculated for

C₉H₁₂N₄O (Mw = 192.38 gmol⁻¹): C, 56.24; H, 6.29; N,

29.15; O, 8.32%. Found: C, 55.71; H, 6.37; N, 29.01; O,

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3

and 1441 m (C=C arom.), 739 m (C–H band (ortho)). ¹H

NMR (400 MHz, DMSO-d₆, δ (ppm)): 4.14 (s, 2H, H2–N4),

7.57 (t, 1H, H–C4, ³J_4,3=³J_4,5=7.7 Hz), 7.71 (t, 1H, H–C5,

H–C6=H–C2, J_2,3= ³J_6,5= 8.4 Hz), 8.40 (s, 1H, H–N3),

1

10.80 (s, 1H,H–N2). Isomer Z: H NMR (400 MHz,

DMSO-d₆, δ (ppm)): 4.10 (s, 2H, H2–N4), 7.38 (s, 1H,

³J_5,4= ³J_5,6= 7.7 Hz), 7.98 (d, 1H, H–C3, J_3,4= 7.7 Hz),

H–C7), 8.01 (d, 2H, H–C5=H–C3 J_3,2= ³J_5,6= 8.4 Hz),

3

8.16 (s, 1H, H–C7), 8.26 (s, 1H, H–N3), 8.41 (d, 1H, H–C6,

³J_6,5=7.7 Hz), 10.78 (s, 1H, H–N2). ¹³C NMR (126 MHz,

DMSO-d₆, δ (ppm)): 124.75 (C3), 128.53 (C1), 129.24 (C6),

131.06 (C4), 133.65 (C5), 135.30 (C7), 148.24 (C2), 157.18

(C8).

8.21 (d, 2H, H–C6=H–C2, J_2,3= ³J_6,5= 8.4 Hz), 8.30 (s,

1H, H–N3), 11.30 (s, 1H, H–N2) (Zelenin et al. 1999).

2‑Methoxybenzaldehyde carbohydrazone (11)

3‑Nitrobenzaldehyde carbohydrazone (9)

White substance, recrystallized from ethanol. Yield:

77%. m.p. 194 °C. Elemental analysis: Calculated

for C₉H₁₂N₄O₂(Mw= 208.38 gmol⁻¹): C, 58.81; H,

5.92; N, 27.43; O, 7.83%. Found: C, 58.33; H, 5.99; N,

27.48; O, 8.20%. IR (KBr, cm⁻¹) ν_max: 3300 m (NH₂),

3091 m (NH), 2998 m, 2841 m and 1465 m (O–CH₃),

1681 s (C=O), 1636 m (C=N), 1522 s and 1481 m (C=C

Yellow substance, recrystallized from ethanol. Yield: 61%.

m.p. 235 °C. Elemental analysis: Calculated for C₈H₉N₅O₃

(Mw= 223.44gmol⁻¹): C, 43.05; H, 4.06; N, 31.38; O,

21.50%. Found: C, 43.14; H, 4.17; N, 31.37; O, 21.32%.

IR (KBr, cm⁻¹) ν_max: 3327 m (NH₂), 3095 m (NH), 1718 s

(C=O), 1616 m (C=N), 1530 s and 1354 s (NO), 1479 m

1

arom.), 754 m (C–H band (ortho)). H NMR (400 MHz,

1

(C=C arom.), 737 m and 674 m (C–H band (meta)). H

DMSO-d₆, δ (ppm)): 3.82 (d, J = 8.9 Hz, 3H), 4.07 (s, 2H,

H2–N4), 6.91–6.97 (m, 1H, H–C5), 7.03 (t, 1H, H–C3,

³J_3,4= 8.2 Hz), 7.26–7.41 (m, 1H, H–C4), 7.90–8.02 (m,

2H, H–C6, H–N3), 8.19 (s, 1H, H–C7), 10.39 (s, 1H,

H–N2). ¹³C NMR (126 MHz, DMSO-d₆, δ (ppm)): 56.06

(OCH₃), 111.98 (C3), 121.02 (C1), 123.21 (C5), 126.26

(C6), 130.88 (C4), 136.08 (C7), 157.56 (C2), 157.62 (C8).

NMR (400 MHz, DMSO-d₆, δ (ppm)): 4.10 (s, 2H, H2–N4),

7.66 (t, 1H, H–C5, ³J_5,6=³J_5,4=8.0 Hz), 7.96 (s, 1H, H–C7),

3

8.16 (dd, 2H, H–C4=H–C6, J_6,5, J_4,5= 8.0 Hz), 8.37 (s,

1H, H–C2), 8.62 (s, 1H, H–N3), 10.62 (s, 1H, H–N2). ¹³

C

NMR (126 MHz, DMSO-d₆, δ (ppm)): 121.20 (C2), 123.65

(C4), 130.48 (C5), 133.42 (C6), 137.24 (C1), 138.18 (C7),

148.85 (C3), 157.33 (C8).

4‑Nitrobenzaldehyde carbohydrazone (10)

3‑Methoxybenzaldehyde carbohydrazone (12)

Yellow substance, recrystallized from ethanol. Yield: 66%.

m.p. 220 °C. Elemental analysis: Calculated for C₈H₉N₅O₃

(Mw= 223.44 g mol⁻¹): C, 43.05; H, 4.06; N, 31.38; O,

21.50%. Found: C, 43.21; H, 4.12; N, 31.44; O, 21.23%.

IR (KBr, cm⁻¹) ν_max: 3329 m (NH₂), 3084 m (NH),

1682 s (C=O), 1615 m (C=N), 1507 s and 1340 s (NO),

1526 m (C=C arom.), 844 m (C–H band (para)). Ratio

White substance, recrystallized from methanol. Yield:

87%. m.p. 189 °C. Elemental analysis: Calculated for

C₉H₁₂N₄O₂(Mw= 208.38 gmol⁻¹): C, 58.81; H, 5.92; N,

27.43; O, 7.83%. Found: C, 58.15; H, 6.09; N, 27.27; O,

8.49%. IR (KBr, cm⁻¹) ν_max: 3326 m (NH₂), 3062 m (NH),

2997 m, 2837 m and 1454 m (O–CH₃), 1678 s (C=O),

1596 m (C=N), 1536 s and 1453 m (C=C arom.), 692 m

and 783 m (C–H band (meta)). Ratio E:Z isomers (75:25).

Isomer E: ¹H NMR (400 MHz, DMSO-d₆, δ (ppm)): 3.80

(d, J = 8.9 Hz, 3H), 4.05 (s, 2H, H2–N4), 6.90 (d, 1H,

1

E:Z isomers (77:23). Isomer E: H NMR (400 MHz,

DMSO-d₆, δ (ppm): 4.15 (s, 2H, H2–N4), 7.94 (s, 1H,

3

H–C7), 8.02 (d, 2H, H–C5=H–C3 J_3,2= ³J_5,6= 8.4 Hz),

3

8.19 (d, 2H, H–C6=H–C2, J_2,3= ³J_6,5= 8.4 Hz), 8.32 (s,

H–C4, J_4,5= 8.0 Hz), 7.16–7.24 (m, 1H, H–C6), 7.28 (t,

1H, H–N3), 10.76 (s, 1H,H–N2). ¹³C NMR (126 MHz,

DMSO-d₆, δ (ppm)): 124.19 (C2=C6), 127.93 (C3=C5),

138.12 (C1), 141.75 (C4), 147.99 (C7), 157.20 (C8).

1H, H–C5, J_5,4= 8,0 Hz), 7.41 (s, 1H, H–C2), 7.84 (s,

3

1H, H–N3), 8.16 (s, 1H, H–C7), 10.41 (s, 1H, H–N2).

¹³C NMR (126 MHz, DMSO-d₆, δ (ppm)): 55.70 (OCH₃),

110.93 (C2), 116.04 (C4), 120.33 (C6), 130.03 (C5),

136.66 (C1), 140.52 (C7), 157.56 (C3), 160.02 (C3). Iso-

mer Z: ¹H NMR (400 MHz, DMSO-d₆, δ (ppm)): 3.81 (d,

J = 8.9 Hz, 3H), 4.05 (s, 2H, H2–N4), 6.97 (d, 1H, H–C4,

³J_4,5= 7.9 Hz), 7.35 (d, 2H, H–C5=H–C6, ³J_4,5= 7.7 Hz),

7.41 (s, 1H, H–C2), 7.84 (s, 1H, H–N3), 8.16 (s, 1H,

H–C7), 10.76 (s, 1H, H–N2). ¹³C NMR (126 MHz,

DMSO-d₆, δ (ppm)): 55.66 (OCH₃), 111.77 (C2), 115.90

(C4), 120.20 (C6), 130.23 (C5), 136.51 (C1), 143.55 (C7),

147.12 (C3), 152.51 (C3).

1

Isomer Z: H NMR (400 MHz, DMSO-d₆, δ (ppm)):

4.15 (s, 2H, H2–N4), 7.94 (s, 1H, H–C7), 8.02 (d,

3

2H, H–C5=H–C3 J_3,2= ³J_5,6= 8.4 Hz), 8.27 (d, 2H,

3

H–C6=H–C2, J_2,3= ³J_6,5= 8.4 Hz), 8.32 (s, 1H, H–N3),

11.21 (s, 1H,H–N2). ¹³C NMR (126 MHz, DMSO-d₆,

δ (ppm)): 124.37 (C2=C6), 128.15 (C3=C5), 141.36

(C4), 148.03 (C7), 152.23 (C8). Lit. data: E:Z isomers

1

(21:79) Isomer E: H NMR (400 MHz, DMSO-d₆, δ

(ppm): 4.10 (s, 2H, H2–N4), 7.90 (s, 1H, H–C7), 8.01

3

(d, 2H, H–C5=H–C3 J_3,2= ³J_5,6= 8.4 Hz), 8.21 (d, 2H,

1 3

Chemical Papers

4‑Methoxybenzaldehyde carbohydrazone (13)

(C=N), 1518 s and 1491 m (C=Carom.), 829 m (C–H

band (para)), 737 m (C–Cl). ¹H NMR (400 MHz,

DMSO-d₆, δ (ppm)): 4.07 (s, 2H, H2–N4), 7.43 (d,

White substance, recrystallized from methanol. Yield: 69%.

m.p. 178 °C. Elemental analysis: Calculated for C₉H₁₂N₄O₂

(Mw = 208.38 gmol⁻¹): C, 58.81; H, 5.92; N, 27.43; O,

7.83%. Found: C, 58.33; H, 6.15; N, 27.88; O, 7.64%. IR

(KBr, cm⁻¹) ν_max: 3300 m (NH₂), 3091 m (NH), 2952 m,

2834 m and 1421 m (O–CH₃), 1682 s (C=O), 1610 m

(C=N), 1508 s and 1421 m (C–H arom.), 831 m (C–H

3

2H, H–C5=H–C3 J_3,2= ³J_5,6= 8.05 Hz), 7.79 (d,

3

2H, H–C6=H–C2, J_2,3= ³J_6,5= 8.05 Hz), 7.84 (s, 1H,

H–C7), 8.12 (s, 1H, H–N3), 10.46 (s, 1H,H–N2).¹³C NMR

(126 MHz, DMSO-d₆, δ (ppm)): 128.80 (C3=C5), 129.02

(C2=C6), 133.86 (C1), 134.23 (C4), 139.17 (C7), 157.47

(C8) (Warkentin et al. 1977).

1

bend (para)). Isomer E: H NMR (400 MHz, DMSO-d₆,

δ (ppm): 3.78 (s, 3H, O-CH₃), 4.07 (s, 2H, H2–N4), 6.94

3‑Bromobenzaldehyde carbohydrazone (16)

3

(d, 2H, H–C5=H–C3 J_3,2= ³J_5,6= 7.8 Hz), 7.68 (t, 2H,

3

H–C6=H–C2, J_2,3= ³J_6,5= 7.8 Hz), 7.80 (s, 1H, H–C7),

White substance, recrystallized from ethanol. Yield: 53%.

m.p. 192–195 °C. Elemental analysis: Calculated for

C₈H₉N₄OBr (Mw= 257.15 gmol⁻¹): C, 37.38; H, 3.53; N,

21.79; O, 6.22; Br, 31.08. Found: C, 37.14; H, 3.71; N,

21.59; O, 6.77; Br, 30.79%. IR (KBr, cm⁻¹) ν_max: 3302 m

(NH₂), 3088 m (NH), 1704 s (C=O), 1607 m (C=N),

1533 s and 1478 m (C=C arom.), 683 s and 788 m (C–H

band (meta)), 577 m (C–Br). ¹H NMR (400 MHz, DMSO-

d₆, δ (ppm)): 4.10 (s, 2H, H2–N4), 7.32 (t, 1H, H–C5,

³J_5,6=8.1 Hz), 7.60 (d, 2H, H–C4, ³J_4,5=8.1 Hz), 7.60 (d,

2H, H–C6, ³J_6,5=8.1 Hz), 7.80 (s, 1H, H–C2), 8.15 (s, 1H,

H–C7), 8.25 (s, 1H, H–N3), 10.49 (s, 1H, H–N2). ¹³C NMR

(126 MHz, DMSO-d₆, δ (ppm)): 122.72 (C2), 126.68 (C3),

128.93 (C4), 131.05 (C5), 131.95 (C6), 137.55 (C1), 141.88

(C7), 157.42 (C8).

7.95 (s, 1H, H–N3), 10.25 (s, 1H, H–N2). ¹³C NMR

(126 MHz, DMSO-d₆, δ (ppm)): 55.72 (O–CH₃), 114.51

(C3=C5), 127.87 (C1), 128.76 (C2=C6), 140.60 (C7),

157.70 (C8), 160.55 (C4).

1

Lit. data: E:Z isomers (85:15) Isomer E: H NMR

(400 MHz, DMSO-d₆, δ (ppm): 3.76 (s, 3H, O-CH₃),

4.10 (s, 2H, H2–N4), 7.90 (s, 1H, H–C7), 8.01 (d,

3

2H, H–C5=H–C3 J_3,2= ³J_5,6= 8.4 Hz), 8.21 (d, 2H,

3

H–C6=H–C2, J_2,3= ³J_6,5= 8.4 Hz), 8.40 (s, 1H, H–N3),

10.80 (s, 1H,H–N2). Isomer Z: ¹H NMR (400 MHz, DMSO-

d₆, δ (ppm)): 3.76 (O-CH₃), 4.10 (s, 2H, H2–N4), 7.38 (s,

1H, H–C7), 8.01 (d, 2H, H–C5=H–C3 ³J_3,2=³J_5,6=8.4 Hz),

8.21 (d, 2H, H–C6=H–C2, ³J_2,3=³J_6,5=8.4 Hz), 8.30 (s, 1H,

H–N3), 11.30 (s, 1H,H–N2) (Okawara et al. 2006).

3‑Chlorobenzaldehyde carbohydrazone (14)

4‑Bromobenzaldehyde carbohydrazone (17)

White substance, recrystallized from methanol. Yield: 56%.

m.p. 225 °C. Elemental analysis: Calculated for C₈H₉N₄OCl

(Mw=212.70gmol⁻¹): C, 45.19; H, 4.27; N, 26.35; O, 7.52;

Cl, 16.67. Found: C, 45.02; H, 4.15; N, 26.88; O, 7.64;

Cl, 16.31%. IR (KBr, cm⁻¹) ν_max: 3327 m (NH₂), 3089 m

(NH), 1706 s (C=O), 1632 m (C=N), 1535 s and 1480 m

(C=Carom.), 683 m and 790 m (C–H band (meta)), 757 m

(C–Cl). ¹H NMR (400 MHz, DMSO-d₆, δ (ppm)): 4.04 (s,

2H, H2–N4), 7.38 (d, 2H, H–C3, H–C5, ³J_5,6=6.6 Hz) 7.60

(d, 2H, H–C6, ³J_6,5=6.6 Hz), 7.82 (s, 1H, H–C2), 8.00 (s,

1H, H–C7), 8.29 (s, 1H, H–N3), 10.51 (s, 1H, H–N2).¹³C

NMR (126 MHz, DMSO-d₆, δ (ppm)): 126.09 (C2), 126.30

(C4), 129.07 (C5), 130.77 (C6), 134.12 (C3), 137.51 (C1),

142.10 (C7), 157.44 (C8).

White substance, recrystallized from ethanol. Yield: 66%.

m.p. 185 °C. Elemental analysis: Calculated for C₈H₉N₄OBr

(Mw=257.15 gmol⁻¹): C, 37.38; H, 3.53; N, 21.79; O, 6.22;

Br, 31.08. Found: C, 37.56; H, 3.66; N, 21.88; O, 6.46;

Br, 30.44%. IR (KBr, cm⁻¹) ν_max: 3332 m (NH₂), 3098 m

(NH), 1668 s (C=O), 1633 m (C=N), 1518 s and 1490 m

(C=C arom.), 833 m (C–H band (para)), 593 m (C–Br).

¹H NMR (400 MHz, DMSO-d₆, δ (ppm)): 4.03 (s, 2H,

H2–N4), 7.56 (dd, 2H, H–C5=H–C3 ³J_3,2=³J_5,6=7.8 Hz),

7.71 (dd, 2H, H–C6=H–C2, ³J_2,3=³J_6,5=7.8 Hz), 7.82 (s,

1H, H–C7), 8.14 (s, 1H, H–N3), 10.47 (s, 1H,H–N2). ¹³C

NMR (126 MHz, DMSO-d₆, δ (ppm)): 122.58 (C4), 129.06

(C2=C6), 131.93 (C3=C5), 134.57 (C1), 139.32 (C7),

157.45 (C8).

4‑Chlorobenzaldehyde carbohydrazone (15)

4‑Fluorobenzaldehyde carbohydrazone (18)

White substance, recrystallized from ethanol. Yield:

53%. m.p. > 240 °C. Elemental analysis: Calculated for

C₈H₉N₄OCl (Mw= 212.70 gmol⁻¹): C, 45.19; H, 4.27;

N, 26.35; O, 7.52; Cl, 16.67. Found: C, 45.64; H, 4.01;

White substance, recrystallized from ethanol. Yield: 71%.

m.p. 188 °C. Elemental analysis: Calculated for C₈H₉FN₄O

(Mw=196.25 gmol⁻¹): C, 48.98; H, 4.62; N, 28.56; O, 8.16;

F, 9.68%. Found: C, 48.81; H, 4.81; N, 28.77; O, 8.22; F,

9.39%. IR (KBr, cm⁻¹) ν_max: 3320 m (NH₂), 3084 m (NH),

1680 s (C=O), 1609 m (C=N), 1509 s and 1413 m (C=C

N, 26.55; O, 7.81; Cl, 15.99%. IR (KBr, cm⁻¹) ν_max

:

3305 m (NH₂), 3091 m (NH), 1682 s (C=O), 1636 m

1 3

Chemical Papers

arom.), 1097 m (C–F), 839 m (C–H bend (para)). ¹H NMR

(400 MHz, DMSO-d₆, δ (ppm)): 4.08 (s, 2H, H2–N4),

7.10–7.26 (m, 2H, H–C5, H–C3), 7.71–7.92 (m, 3H, H–C7,

the integrals in ¹H NMR spectra pointed to the conclusion

of the isomer ratio (E:Z). The stereochemistry of the mCHs,

which have been found to possess both isomers, was undoubt-

edly established using 2D homonuclear (NOESY) and het-

eronuclear (HSQC and HMBC) NMR techniques. As an

example, the chemical shifts of compound 10 were assigned

by the combined use of one-dimensional (¹H and ¹³C proton

decoupled, Figs. S1 and S2 in ESM) and two-dimensional

NMR experiments such as NOESY, HSQC, and HMBC given

in Figs. S3–S5, respectively. In order to assess the confor-

mation of compound 10 in a solution, the two-dimensional

NOESY sequence was applied (Fig. S3). The E stereochem-

istry was assigned to be major isomer in DMSO d₆solutions

because the NOESY experiments show a correlation of C7–H

and H–N2 and atoms (Fig. S3), which may be present only in

the case of the E isomer (Scheme 2). Moreover, the chemical

shifts of the proton present in Z isomer showed little diference

to those found in the parent compound (Fig. S1). The 7.7:2.3

isomer ratio for compound 10 in DMSO d₆was obtained from

the ¹H NMR spectrum (Fig. S1). Analogously, the analyses

of ¹H NMR data of N2–H proton were used for calculation of

E/Z isomer ratio of other studied compounds. The obtained

results showed that E form dominates in DMSO solution.

H–C6, H–C2), 8.08 (s, 1H, H–N3), 10.39 (s, 1H, H–N2). ¹³

C

NMR (126 MHz, DMSO-d₆, δ (ppm)): 115.84 (C3), 116.06

(C3), 129.19 (C2), 129.27 (C6), 131.88 (C1), 139.36 (C7),

157.57 (C8), 164.47 (C4) (Warkentin et al. 1977).

Results and discussion

Synthesis and compound characterization

¹H and ¹³C NMR spectra of newly synthesized derivatives

of monocarbohydrazones showed good agreement with sig-

nals expected for hydrogen and carbon atoms. Also, spectra

of compounds that are already known showed remarkably

good super position with the given literature data (Božić

et al. 2017a, b; Okawara et al. 2006; Warkentin et al. 1977).

The results of the elemental analysis were within 0.5%

of the theoretical values. In the infrared spectra of

monocarbohydrazones, absorptions between 1668 and

1718 cm⁻¹were assigned to the ν(C=O) stretching. Sig-

nals recorded between 3062 and 3098 cm⁻¹were assigned

to ν(N–H) vibrations, while the absorptions between 1596

and 1645 cm⁻¹were attributed to the ν(C=N) band. Giv-

ing the structure of all synthesized compounds, signals of

ν(C=C arom.) are presented with two bands in the range of

1508–1593 and 1413–1491 cm⁻¹. The proof that all synthe-

sized compounds belong to the group of monocarbohydra-

zones is expressed through the existence of ν(NH₂) vibra-

tions that were rec orded in the range of 3283–3361 cm⁻¹

(Božić et al. 2017a, b).

Geometry optimization of monocarbohydrazones

Carbohydrazones can exist in keto/enol tautomeric forms,

and they could adopt E or Z confguration around the C=N

bond (Božić et al. 2017b; Zelenin et al. 1999). Optimized

geometries have shown that E isomers mainly adopt planar

confgurations with the angle between the phenyl group and

carbohydrazide moiety around 14° (Table S1). Only in com-

pound 8, this angle is somewhat larger due to steric clash

between bulky subs tituent in ortho position and hydrogen

atom Hc (Schemes 1, 2 and Fig. S6). Much larger deviations

from planarity exist in optimized geometries of Z isomers

due to steric hindrance between ortho hydrogen (or substitu-

ent) on phenyl group and H1 hydrogen atom from carbohy-

drazide moiety; the angle between phenyl group and carbo-

hydrazide moiety is in the range between 20.00 and 68.15°

It is known that mCHs, as Schif bases, show E/Z isomeri-

zation caused by the presence of the imino group (Okawara

et al. 2006; Zelenin et al. 1999). Isomerization of synthe-

sized monocarbohydrazones along the with numeration of

atoms of interest is given in Scheme 2.

The assignation from NMR spectra indicated that the

major product can also be an E and Z isomer. The ratio of

Scheme 2 Isomerization of monocarbohydrazones with numeration of atoms of interest (Wiggins et al. 2009)

1 3

Chemical Papers

(Table S1). Energies obtained from ab initio calculations at

MP2/6-311G(d,p) level of theory have shown that Z isomer

is from 2.38 to 5.84 kcal/mol more stable for all compounds

(Table S2), except for compound 2 where E confguration

shows higher stability (0.15 kcal mol⁻¹) due to the formation

of intermolecular hydrogen bond.

so it contains another parameter more in the equation given

below:

ꢀ = ꢀ₀+ aSA + bSB + cSP + dSdP,

(2)

where ν is the frequency in a given solvent, ν₀is the solute

property of the reference system, cyclohexane, SA represents

the hydrogen bond donating ability (HBD), SB is a measure

of the hydrogen bond accepting ability (HBA), SP describes

the polarizability and SdP represents the dipolarity of the

solvent. Correlation coefcients a, b, c and d describe the

sensitivity of the absorption maxima to diferent types of

solvent–solute interactions (Catalán and Hopf 2004; Catalán

2009).

The efect of solvent on spectral behavior

of monocarbohydrazones

The absorption spectra of the same molecule in the gaseous

state and at the presence of a solvent always difer from one

another. Depending on the properties of the solvent and its

ability to enter into various physical or chemical interac-

tions with the dissolved substance, a change in the absorp-

tion spectrum relative to the spectrum in the gaseous state is

expected (Reichardt 2003). Intermolecular interactions and

the efects of specifc and nonspecifc solvent–solute interac-

tions on the UV absorption maxima shifts were studied by

the method of linear solvation energy relationship (LSER).

There are a large number of models describing these

interactions, but Kamlet–Taft’s and Catalan’s models are

the most commonly used.

Absorption spectra of carbohydrazones were recorded

in the range from 200 to 400 nm in nineteen solvents of

diferent properties. Figure 1 shows the absorption spectra

of compound 4 in protic and aprotic solvents. For all other

compounds, similar spectra were obtained.

Spectra of all investigated compounds show two or three

absorption maxima. The frst one occurs at about 220 nm,

but it was excluded from further analysis because some sol-

vents in that part of the spectrum absorb electromagnetic

radiation and overlap the spectrum of the compound. The

second one, used for analysis, occurs in the range from 280

to 330 nm, depending on the substituent present and solvent

used. After the process of deconvolution of the absorption

spectra, only one absorption maximum was observed in

all solvents. It is assumed that the analyzed maxima come

as a result of n → π* transition in molecules. Due to the

diversity of substituents present, the absorption maxima of

compounds tested occur in a wide range of wavelengths.

Absorption frequencies at the maximum of absorbance and

the values of observed molar absorptivity for all compounds

Kamlet–Taft’s model is described by Eq. (1):

ꢀ = ꢀ₀+ sꢁ^∗+ aꢂ + bꢃ,

(1)

where ν is the frequency in a given solvent, ν₀is the fre-

quency in the standard solvent, π* is dipolarity/polarizabil-

ity, α acidity and β basicity of the solvent, while s, a and b

are regression coefcients of the given equation (Taft and

Kamlet 1976; Kamlet and Taft 1976; Kamlet et al. 1977).

Unlike Kamlet–Taft’s, Catalan’s model has separated the

infuence of the polarizability and dipolarity of the solvent,

Fig. 1 Spectra of compound 4 in protic (a) and aprotic (b) solvents

1 3

Chemical Papers

1 3

Chemical Papers

Table 2 Absorption frequencies, ν_max×10⁻³(cm⁻¹) and values of molar absorptivity, ε (mol⁻¹dm³cm⁻¹), in aprotic solvents

Com-

AcN

DMSO

DMF

DCM

Chloroform EtAc

THF

1,4-Dioxane Diethyl ether

pound/

solvent

1

35.06

35.01

34.98

34.93

34.91

34.92

34.87

34.82

34.80

(21,450)

(20,753)

(20,335)

(21,793)

(20,412)

(21,054)

(20,215)

(20,825)

(25,155)

2

35.80

35.78

35.74

35.77

35.66

35.69

35.66

35.58

35.55

(20,137)

(18,557)

(18,098)

(20,640)

(14,960)

(22,396)

(17,522)

(14,278)

(23,754)

3

34.94

34.86

34.82

34.79

34.78

34.74

34.72

34.67

34.65

(15,864)

(14,914)

(14,788)

(15,968)

(11,042)

(17,088)

(13,992)

(15,085)

(19,099)

4

34.23

34.20

34.19

34.16

34.13

34.07

34.08

34.05

34.01

(30,865)

(28,282)

(29,227)

(29,548)

(21,186)

(32,732)

(29,487)

(28,965)

(34,662)

5

34.59

34.54

34.50

34.46

34.42

34.44

34.33

34.28

34.20

(23,239)

(18,350)

(22,483)

(24,210)

(23,015)

(25,357)

(22,494)

(23,393)

(27,288)

6

34.71

34.66

34.64

34.59

34.55

34.52

34.49

34.48

(24,244)

(24,227)

(23,806)

(25,679)

(22,397)

(26,340)

(24,244)

(23,668)

(29,519)

7

34.51

34.46

34.43

34.39

34.32

34.29

34.27

34.26

34.20

(27,264)

(23,230)

(27,706)

(23,608)

(28,591)

(26,305)

(26,881)

(28,893)

8

36.80

36.72

36.71

36.68

36.65

36.62

36.58

36.54

36.51

(16,456)

(15,829)

(13,381)

(15,767)

(15,195)

(17,826)

(13,176)

(12,135)

(15,836)

9

33.37

33.08

32.94

32.91

32.69

32.63

32.61

32.31

32.22

(25,060)

(24,433)

(24,407)

(27,199)

(25,172)

(27,930)

(24,877)

(20,883)

(25,369)

10

11

12

13

14

15

16

17

18

30.39

30.32 (9,243) 30.27

30.23

30.24

30.17

30.12

30.14

30.07

(12,125)

(13,368)

(14,588)

(10,004)

(22,088)

(12,232)

(12,211)

(13,958)

35.66

35.60

35.58

35.52

35.54

35.51

35.48

35.46

35.394

(16,012)

(11,987)

(14,519)

(14,622)

(14,112)

(18,021)

(14,215)

(16,879)

(1,924)

34.97

34.95

34.91

34.88

34.84

34.81

34.78

34.72

(21,607)

(18,610)

(14,476)

(19,615)

(19,831)

(28,290)

(18,310)

(19,250)

(22,234)

34.39

34.37

34.34

34.32

34.28

34.23

34.19

34.18

(24,768)

(20,876)

(23,210)

(23,031)

(22,494)

(23,900)

(22,165)

(23,323)

(26,638)

32.84

32.81

32.73

32.67

32.71

32.62

32.67

32.56

32.48

(23,104)

(19,099)

(21,564)

(20,992)

(20,193)

(24,659)

(21,062)

(20,412)

(24,296)

34.55

34.51

34.47

34.41

34.40

34.41

34.31

34.33

34.27

(22,424)

(18,608)

(17,898)

(22,945)

(20,335)

(23,147)

(19,426)

(21,184)

(22,473)

32.96

32.92

32.85

32.86

32.75

32.79

32.77

32.68

32.60

(20,600)

(16,542)

(17,640)

(20,367)

(18,532)

(23,228)

(19,393)

(18,522)

(18,625)

34.42

34.38

34.32

34.27

34.25

34.22

34.17

(23,926)

(22,015)

(21,778)

(24,273)

(23,147)

(26,983)

(23,917)

(23,303)

(27,292)

35.22

35.18

35.14

35.13

35.07

35.04

35.05

35.02

34.98

(17,715)

(19,510)

(36,312)

(20,753)

(19,031)

(16,598)

(19,582)

(14,565)

(23,299)

in protic and aprotic compounds are shown in Tables 1 and

2, respectively.

shown. As can be seen, the hypsochromic shifting of absorp-

tion maxima is represented. This dependency also confrms

the previously stated assumption that the observed absorp-

tion maxima of the investigated compounds originate from

the n → π* transition in the molecule (Antić-Jovanović

2006).

Based on the results shown in Tables 1 and 2, it is clear

that the hypsochromic displacement of the absorption max-

ima occurs with increasing the polarity of the solvent. This

is characteristic of n→π* transitions in molecules (Antić-

Jovanović 2006). Table 3 shows the empirical parameters of

the solvents used: E_T^N—empirical polarity parameter, Kam-

let–Taft’s and Catalan’s solvent parameters and Hansen’s

solubility parameters: δd—energy from dispersion forces,

δp—energy from dipolar intermolecular forces, δh—energy

from hydrogen bonds between molecules.

A quantitative description of the interactions between

the investigated compounds and the surrounding medium

is obtained with two models. Correlations of absorption

maxima with Kamlet–Taft’s parameters (Table 3) are given

in Eq. (1), and the values of their regression coe f cients, as

well as the statistical parameters, are given in Table 4.

By observing the values of the correlation coef cients

of equations for each compound (r²= 0.915–0.971), it

In Fig. 2, the correlation of the absorption maxima of

compound 4 with empirical polarity parameter, E_T^N, is

1 3

Chemical Papers

Table 3 Parameters of the

solvents used (Antić–Jo vanović

2006 ; Catalán and Hopf 2004;

Catalán 2009 ; Hansen 2007 ;

Kamle t and Taft 1976 ; Kamlet

et al. 1977; Taft and Kamlet

1976 )

E^N

Solvent

Kamlet–Taft’s solvent Catalan’s solvent parameters

parameters

Hansen’s solubility

parameters

T

α

β

π

SA

SB

SP

SdP

δd

δp

δh

Water

1.000 1.17 0.47 1.09 1.062 0.025 0.681 0.997 15.6 16.0 42.3

0.762 0.98 0.66 0.60 0.605 0.545 0.608 0.904 15.1 12.3 22.3

0.654 0.86 0.75 0.54 0.400 0.658 0.633 0.783 15.8

0.617 0.84 0.90 0.52 0.367 0.782 0.658 0.748 16.0

0.586 0.84 0.84 0.47 0.341 0.809 0.674 0.655 16.0

0.568 0.84 0.86 0.40 0.319 0.860 0.687 0.587

0.552 0.79 0.84 0.40 0.311 0.828 0.657 0.684 15.1

0.546 0.76 0.84 0.48 0.283 0.830 0.633 0.808 15.8

Methanol

Ethanol

n-Propanol

n-Butanol

n-Pentanol

i-Butanol

i-Propanol

t-Butanol

Acetic acid

AcN

8.8 19.4

6.8 17.4

5.7 15.8

–

5.7 15.9

6.1 16.4

–

0.389 0.42 0.93 0.41 0.145 0.928 0.632 0.732

0.648 1.12 0.45 0.64 0.689 0.390 0.651 0.676 14.5

0.460 0.19 0.40 0.75 0.044 0.286 0.645 0.974 15.3 18.0

–

8.0 13.5

6.1

DMSO

DMF

0.444 0.00 0.76 1.00 0.072 0.647 0.830 1.000 18.4 16.4 10.2

0.386 0.00 0.69 0.88 0.031 0.613 0.759 0.977 17.4 13.7 11.3

DCM

Chloroform

EtAc

THF

1,4-Dioxane

0.319 0.13 0.10 0.82 0.040 0.178 0.761 0.769 18.2

0.259 0.44 0.00 0.58 0.047 0.071 0.783 0.614 17.8

0.228 0.00 0.45 0.55 0.000 0.542 0.656 0.603 15.8

0.207 0.00 0.55 0.58 0.000 0.591 0.714 0.634 16.8

0.164 0.00 0.37 0.55 0.000 0.444 0.737 0.312 19.0

6.3

3.1

5.3

5.7

1.8

2.9

6.1

5.7

7.2

8.0

7.4

5.1

Diethyl ether 0.117 0.00 0.47 0.27 0.000 0.562 0.617 0.385 14.5

slightly lower infuence has the acidity of the solvent (values

of the regression coefcient a), while the smallest impact

on the maxima shifting of all carbohydrazones has alkalin-

ity, described with regression coefcient b. A positive sign

in front of each of these regression coefcients indicates

that with the increase in polarizability/dipolarity, acidity

and alkalinity of the solvent, hypsochromic shifting of the

absorption maxima of the tested compounds is expected.

In addition to the Kamlet–Taft’s, for the description of the

solvent–solute interactions of the investigated carbohydra-

zones, Catalan’s model was also used. Results for the tested

compounds, in all solvents, obtained by applying this model

are shown in Table 5.

By observing the results of Catalan’s model, it can be

noticed that the regression coefcient a has the highest

value (with exception for compounds 9 and 11, where sol-

vent’s polarizability has the most dominant efect), which

means that the acidity of the solvent has the greatest infu-

ence on the spectral behavior of the carbohydrazones.

Slightly smaller efects have polarizability and dipolarity

of solvent (coefcient values c and d). In the end, as with

Kamlet–Taft’s model, the smallest infuence has the alka-

linity of the solvent—coefcient b has the least value for

all compounds. The positive sign in front of the regression

coefcients a, b and d means that hypsochromic shifting

of the absorption maxima will occur in case of an increase

in the acidity, basicity, and dipolarity of the solvent. The

negative sign in front of the coefcient c indicates that with

Fig. 2 Correlation obtained between absorption frequencies of com-

pound 4 with empirical parameter of the solvents used

can be concluded that the model used is suitable for the

interpretation of solvent–solute interactions of synthesized

carbohydrazones.

The highest values are obtained for regression coef-

cient s, which indicates that the polarizability/dipolarity of

the solvents has the greatest impact on the spectral shift-

ing of investigated compounds. (Exceptions are compounds

3, 10 and 11 where coefcient a has the biggest value.) A

1 3

Chemical Papers

Table 4 Regression coefcients

of the obtained equations by

Kamlet–Taft’s model

Compound ν₀×10⁻³, cm⁻¹

a×10⁻³, cm⁻¹

b×10⁻³, cm⁻¹

s×10⁻³, cm⁻¹

r^{2 a}

SD^b

F^c

1

34.634 ( 0.043) 0.298 ( 0.024) 0.097 ( 0.041) 0.335 ( 0.048) 0.940 0.042 78

35.436 ( 0.039) 0.218 ( 0.021) 0.111 ( 0.037) 0.290 ( 0.043) 0.923 0.037 60

34.458 ( 0.049) 0.398 ( 0.027) 0.115 ( 0.047) 0.350 ( 0.055) 0.952 0.048 99

33.876 ( 0.034) 0.214 ( 0.019) 0.103 ( 0.032) 0.282 ( 0.038) 0.935 0.033 72

33.950 ( 0.072) 0.472 ( 0.040) 0.116 ( 0.068) 0.571 ( 0.080) 0.934 0.069 71

34.295 ( 0.048) 0.327 ( 0.027) 0.076 ( 0.046) 0.341 ( 0.054) 0.934 0.047 71

33.993 ( 0.043) 0.332 ( 0.024) 0.145 ( 0.041) 0.402 ( 0.048) 0.955 0.041 105

36.360 ( 0.044) 0.288 ( 0.024) 0.090 ( 0.042) 0.339 ( 0.049) 0.934 0.043 71

31.747 ( 0.156) 0.962 ( 0.086) 0.409 ( 0.147) 1.129 ( 0.173) 0.929 0.150 66

29.860 ( 0.074) 0.466 ( 0.041) 0.071 ( 0.069) 0.433 ( 0.082) 0.921 0.071 58

35.292 ( 0.040) 0.269 ( 0.022) 0.100 ( 0.038) 0.255 ( 0.044) 0.935 0.038 72

34.590 ( 0.029) 0.299 ( 0.016) 0.094 ( 0.028) 0.310 ( 0.033) 0.971 0.028 165

34.041 ( 0.028) 0.243 ( 0.016) 0.107 ( 0.027) 0.263 ( 0.031) 0.962 0.027 126

32.255 ( 0.068) 0.374 ( 0.038) 0.131 ( 0.064) 0.503 ( 0.076) 0.915 0.066 54

34.129 ( 0.045) 0.279 ( 0.025) 0.129 ( 0.043) 0.303 ( 0.051) 0.928 0.044 65

32.440 ( 0.049) 0.315 ( 0.027) 0.134 ( 0.047) 0.415 ( 0.055) 0.936 0.048 73

34.004 ( 0.051) 0.312 ( 0.028) 0.085 ( 0.048) 0.331 ( 0.057) 0.922 0.049 60

34.798 ( 0.045) 0.301 ( 0.025) 0.105 ( 0.043) 0.342 ( 0.050) 0.936 0.043 74

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

^aCorrelation coefcient

^bStandard deviation

^cFisher’s correlation test

Table 5 Regression coefcients of Catalan’s model

Compound ν₀×10⁻³, cm⁻¹a×10⁻³, cm⁻¹

b×10⁻³, cm⁻¹

c×10⁻³, cm⁻¹

d×10⁻³, cm⁻¹

r²

SD

F

Solvents

excluded

1

2

3

4

5

6

7

8

34.866 ( 0.104) 0.416 ( 0.030) 0.035 ( 0.029)

−0.232 ( 0.140) 0.290 ( 0.041) 0.971 0.030 119

–

b, c

35.671 ( 0.136) 0.281 ( 0.036) 0.045 ( 0.033)

−0.214 ( 0.170) 0.239 ( 0.046) 0.938 0.032

−0.423 ( 0.316) 0.219 ( 0.086) 0.926 0.059

0.247 ( 0.052) 0.919 0.038

46

38

40

61

a

b, c

34.916 ( 0.253) 0.528 ( 0.067)

–

33.905 ( 0.133) 0.310 ( 0.039) 0.055 ( 0.037)

–

34.164 ( 0.227) 0.701 ( 0.066)

34.522 ( 0.118) 0.470 ( 0.036)

–

0.391 ( 0.089) 0.946 0.065

−0.190 ( 0.159) 0.259 ( 0.046) 0.967 0.034 104

–

b, c

34.324 ( 0.160) 0.456 ( 0.042) 0.052 ( 0.039)

−0.252 ( 0.200) 0.277 ( 0.054) 0.961 0.041

0.262 ( 0.061) 0.933 0.044

73

48

39

40

60

55

49

45

44

55

97

36.459 ( 0.155) 0.419 ( 0.046)

33.149 ( 0.617) 1.123 ( 0.163)

30.452 ( 0.288) 0.620 ( 0.076)

–

b, c

9

−1.460 ( 0.772) 0.953 ( 0.210) 0.929 0.144

−0.525 ( 0.360) 0.230 ( 0.098) 0.931 0.067

−0.439 ( 0.170) 0.192 ( 0.046) 0.952 0.032

0.231 ( 0.057) 0.940 0.042

b, c

10

11

12

13

14

15

16

17

18

35.708 ( 0.136) 0.324 ( 0.036) 0.036 ( 0.032)

34.651 ( 0.146) 0.439 ( 0.043) 0.068 ( 0.041)

34.038 ( 0.130) 0.361 ( 0.038) 0.087 ( 0.037)

–

0.219 ( 0.051) 0.933 0.037

0.360 ( 0.085) 0.928 0.062

32.321 ( 0.217) 0.574 ( 0.064)

–

b, c

34.444 ( 0.173) 0.372 ( 0.046) 0.062 ( 0.042)

−0.303 ( 0.216) 0.233 ( 0.059) 0.937 0.040

0.268 ( 0.220) 0.297 ( 0.060) 0.948 0.041

−0.367 ( 0.213) 0.229 ( 0.058) 0.948 0.040

−0.287 ( 0.157) 0.226 ( 0.043) 0.970 0.029

b, c

32.775 ( 0.176) 0.421 ( 0.047)

34.393 ( 0.171) 0.411 ( 0.045)

35.140 ( 0.126) 0.414 ( 0.033)

–

^aError greater than the value

^bEthyl acetate

^cDiethyl ether

1 3

Chemical Papers

theoreticall y calculated absorption frequencies (ν_calc) based

on Eqs. (1) and (2). Dependencies obtained are shown in

Fig. 3.

Correlation coefficient for Kamlet–Taft’s model was

r²=0.998 and for Catalan’s was r²=0.993 (Fig. 3). Judging

by the values, both models applied are suitable for the inter-

pretation of the efect of the solvent on maxima shifting of

the tested monocarbohydrazones (Bauer et al. 2008; Riedel

and Spange 2012). By observing the numerical values of

the regression coefcients within Kamlet–Taft’s model, it

can be concluded that the infuences of polarizability/dipo-

larity and acidity of the solvents are almost equal, while

Catalan’s model shows that acidity has a principal impact on

maxima shifting of the monocarbohydrazones. (Exceptions

are compounds 9 and 11, where solvents’ polarizability has

the most dominant efect.) On the frst site, two models show

diferent results that can be explained with the fact that the

infuence of the polarizability/dipolarity (π^*) within Kam-

let–Taft’s model is divided into two scales when Catalan’s

model is observed—SP and SdP scales. The sum of shares

of all nonspecifc interactions (dipolarity and polarizability)

obtained by Catalan’s model prevails over the acidity of the

solvents used and that is in agreement with the results of

Kamlet–Taft’s model.

Fig. 3 Correlation of ν_expwith ν_calc

the increase in polarizability of the solvent bathochromic

shifting of the maxima will occur.

The correctness of the applied models was confrmed

by obtaining linear dependences with good correlation

coefcients between experimentally determined (ν_exp) and

Table 6 Results of correlations with Hansen’s solubility parameters

Comp.

ν₀×10⁻³,cm⁻¹

d×10⁻³, cm⁻¹

p×10⁻³, cm⁻¹

h×10⁻³, cm⁻¹

r²

SD

F

Solvents excluded

a, b

1

2

3

4

5

6

7

8

35.568 ( 0.179)

36.227 ( 0.144)

35.818 ( 0.276)

34.527 ( 0.126)

35.117 ( 0.269)

35.299 ( 0.200)

35.046 ( 0.214)

37.239 ( 0.155)

35.626 ( 0.631)

30.833 ( 0.371)

36.328 ( 0.168)

35.543 ( 0.199)

34.912 ( 0.137)

33.272 ( 0.240)

35.025 ( 0.138)

33.560 ( 0.196)

35.021 ( 0.218)

35.676 ( 0.163)

−0.043 ( 0.010)

−0.036 ( 0.008)

−0.064 ( 0.015)

−0.026 ( 0.007)

−0.050 ( 0.015)

−0.047 ( 0.011)

−0.046 ( 0.012)

−0.039 ( 0.009)

−0.175 ( 0.035)

−0.042 ( 0.020)

−0.049 ( 0.009)

−0.042 ( 0.011)

−0.038 ( 0.008)

−0.042 ( 0.013)

−0.040 ( 0.008)

−0.049 ( 0.011)

−0.047 ( 0.012)

−0.039 ( 0.009)

0.006 ( 0.002)

–

0.011 ( 0.002)

0.008 ( 0.001)

0.013 ( 0.002)

0.008 ( 0.001)

0.020 ( 0.002)

0.012 ( 0.002)

0.010 ( 0.001)

0.025 ( 0.005)

0.016 ( 0.003)

0.008 ( 0.001)

0.010 ( 0.002)

0.007 ( 0.001)

0.016 ( 0.002)

0.009 ( 0.001)

0.011 ( 0.002)

0.012 ( 0.001)

0.926

0.928

0.903

0.934

0.933

0.930

0.925

0.944

0.917

0.907

0.922

0.910

0.934

0.929

0.946

0.930

0.909

0.947

0.047

0.037

0.070

0.032

0.071

0.050

0.054

0.039

0.158

0.080

0.042

0.050

0.034

0.060

0.036

0.049

0.055

0.041

46

48

34

47

56

49

45

56

37

26

43

37

47

48

64

49

36

65

a, b, c

a, d

a, b, d

0.003 ( 0.002)

0.007 ( 0.004)

0.005 ( 0.003)

0.006 ( 0.003)

0.006 ( 0.002)

0.020 ( 0.009)

0.006 ( 0.005)

0.003 ( 0.002)

–

0.003 ( 0.002)

0.006 ( 0.003)

0.005 ( 0.002)

0.006 ( 0.003)

0.004 ( 0.002)

A

a, d

a, b, d

a, b, d, e, f

a, d

9

10

11

12

13

14

15

16

17

18

a, d

a, b, d

a, d

a, b

a, d

^aDiethyl ether

^bTHF

^cDCM

^dEtAc

^eCH₃COOH

^fEtOH

1 3

Chemical Papers

Table 8 Regression coefcients of Hammett’s equation for all sol-

vents used

Solvent

ν₀×10⁻³, cm⁻¹ρ×10⁻³, cm⁻¹

r²

SD

Electron acceptors

Water

Methanol

Ethanol

n-Propanol

n-Butanol

n-Pentanol

i-Butanol

i-Propanol

t-Butanol

Acetic acid

AcN

DMSO

DMF

DCM

Chloroform

EtAc

35.974( 0.154) −6.395( 0.454) −0.983 0.304

35.781( 0.167) −6.433( 0.494) −0.980 0.330

35.716( 0.175) −6.470( 0.515) −0.979 0.345

35.691( 0.164) −6.507( 0.484) −0.981 0.324

35.670( 0.174) −6.601( 0.513) −0.979 0.343

35.625( 0.175) −6.599( 0.517) −0.979 0.346

35.690( 0.179) −6.659( 0.526) −0.979 0.352

35.691( 0.169) −6.715( 0.498) −0.981 0.333

35.556( 0.175) −6.634( 0.517) −0.979 0.346

35.739( 0.169) −6.459( 0.498) −0.980 0.333

35.616( 0.169) −6.607( 0.498) −0.981 0.333

35.576( 0.170) −6.628( 0.981) −0.981 0.335

35.535( 0.171) −6.664( 0.503) −0.981 0.336

35.506( 0.174) −6.668( 0.513) −0.980 0.343

35.475( 0.171) −6.635( 0.504) −0.980 0.337

35.465( 0.174) −6.696( 0.512) −0.980 0.342

35.439( 0.164) −6.701( 0.483) −0.982 0.323

35.395( 0.179) −6.668( 0.527) −0.979 0.353

Fig. 4 Spectra of all investigated compounds recorded in methanol

Table 7 Hammett’s constants of substituents

Substituent

σ_m,p

Substituent

σ_m,p

Substituent

σ_m,p

THF

1,4-Dioxane

4-H

4-F

4-Cl

4-Br

3-Cl

0.00

0.06

0.23

0.37

3-Br

0.39

0.71

0.78

0.12

3-CH₃

4-CH₃

4-OCH₃

4-OH

−0.07

−0.17

−0.27

−0.37

Diethyl ether 35.359( 0.178) −6.735( 0.524) −0.979 0.351

Electron donors

3-NO₂

4-NO₂

3-OCH₃

3-OH

Water

35.352 ( 0.040) 2.407 ( 0.183)

35.160 ( 0.175) 2.340 ( 0.302)

35.071 ( 0.069) 2.256 ( 0.314)

35.017 ( 0.068) 2.063 ( 0.306)

34.974 ( 0.082) 1.906 ( 0.371)

34.955 ( 0.072) 2.073 ( 0.327)

34.993 ( 0.046) 2.064 ( 0.210)

34.995 ( 0.081) 2.099 ( 0.366)

34.879 ( 0.071) 1.986 ( 0.322)

35.120 ( 0.059) 2.376 ( 0.269)

34.944 ( 0.075) 2.069 ( 0.340)

34.891 ( 0.078) 1.994 ( 0.355)

34.861 ( 0.079) 1.962 ( 0.356)

34.810 ( 0.080) 1.887 ( 0.361)

34.789 ( 0.087) 1.951 ( 0.396)

34.782 ( 0.095) 2.105 ( 0.429)

34.737 ( 0.093) 1.947 ( 0.420)

0.991 0.055

0.976 0.090

0.972 0.094

0.968 0.091

0.948 0.110

0.965 0.097

0.985 0.063

0.957 0.109

0.963 0.096

0.981 0.080

0.962 0.101

0.956 0.106

0.954 0.106

0.949 0.108

0.943 0.118

0.943 0.128

0.937 0.125

0.948 0.111

0.941 0.121

Methanol

Ethanol

n-Propanol

n-Butanol

n-Pentanol

i-Butanol

i-Propanol

t-Butanol

Acetic acid

AcN

DMSO

DMF

DCM

Chloroform

EtAc

THF

1,4-Dioxane 34.700 ( 0.082) 1.919 ( 0.371)

Diethyl ether 34.679 ( 0.090) 1.961 ( 0.406)

Fig. 5 Dependences of absorption frequencies from constants of sub-

the investigated compounds and the surrounding medium.

Correlations were made by the method of multiple linear

correlations according to Eq. (3):

stituents in methanol

In addition to the efect of solvent, correlations of the

absorption maxima (Tables 1, 2) with Hansen’s solubility

parameters (Table 3) were made in order to obtain addi-

tional information about the interactions that occur between

ꢀ = ꢀ₀+ dꢁd + pꢁp + hꢁh,

(3)

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Chemical Papers

Table 9 Calculated values of Λ index, Q_CTand D_CTduring electron

of the substituent present on the benzene ring. Quantitative

analysis of this impact is given by applying the linear free

energy relationship (LFER) to Hammett’s equation:

excitation

Compound

Λ index

Q_CT(e⁻)

D_CT(Ǻ)

ꢀ_max= ꢀ₀+ ꢁꢂ_m,p

,

1

2

3

4

5

6

7

8

0.73

0.65

0.70

0.73

0.59

0.73

0.74

0.54

0.52

0.56

0.72

0.71

0.74

0.70

0.73

0.70

0.73

0.530

0.490

0.511

0.507

0.333

0.527

0.512

0.618

0.573

0.724

0.517

0.506

0.552

0.528

0.552

0.529

0.525

2.067

0.926

0.570

0.957

0.783

1.937

1.749

2.923

2.449

0.773

2.220

0.708

0.837

2.175

1.925

2.143

1.795

1.773

(4)

where ν_maxis absorption frequency at the maximum of

absorbance, ν₀represents the wave number in the irrespec-

tive solvent, ρ is a proportionality constant refecting the

sensitivity of the spectral data to the substituent efects,

described by the substituent constant, σ_m,p(Hammett’s con-

stant) (Hammett 1937).

In Fig. 4 , spectra of all compounds recorded in methanol

are represented. Since Hammett’s equation does not give a

description for the substituents in the ortho position, com-

pounds 2, 5, 8 and 11 are left out from the correlations.

As can be seen, most of the compounds tested give

smaller or bigger bathochromic shifts relative to the unsub-

stituted compound, 1 (4-H). The exceptions are compounds

2, 8, 11 and 18 where hypsochromic shifts were noticed.

The numerical values of the Hammett’s constants of sub-

stituents are given in Table 7.

9

10

11

12

13

14

15

16

17

18

Correlating these constants to the absorption maxima of

the compounds tested, linear dependencies are obtained,

such as the dependence in Fig. 5.

where δd is the energy from dispersion forces, δp represents

the energy from dipolar intermolecular forces and δh is the

energy from hydrogen bonds between molecules. d, p, and

h are regression coefcients that show the extent of interac-

tions represented (Hansen 2007). Table 6 shows the results

obtained.

Two separate linear dependences were obtained. The frst,

dependence with the positive slope, represents electron-

donor substituents, while the other is for substituents with

electron-acceptor properties (negative slope), with the devia-

tion for compound 9 (3-NO₂). Coefcients of the obtained

linear correlations are presented in Table 8.

Based on the numerical values of the regression coef-

fcients in Table 6, where regression coefcient d has the

highest value, it can be concluded that the most dominant

forces between tested carbohydrazones and the solvent used

are the dispersion forces. They are followed by the possibil-

ity of building hydrogen bonds (regression coefcient h),

and fnally, with a very small efect, dipolar forces are repre-

sented (regression coefcient p). Results obtained by corre-

lation with Hansen’s solubility parameters are in agreement

with the results obtained by the application of the Kam-

let–Taft’s model, and it can be concluded that nonspecifc

interactions are more dominant and have a greater infuence

on maxima shifting of the monocarbohydrazone derivatives

than the specifc ones.

The absolute value of the proportionality constant,

ρ, determines the extent of substituent’s infuence on the

change of electronic density in the molecule. A positive sign

of the proportionality constants in all solvents in the case

where substituents are electron donors indicates an increased

electron density in the excited state in relation to the basic.

When substituents of the tested derivatives have an electron-

acceptor’s nature, the proportionality constant has a nega-

tive value, which indicates a reduced electron density in the

excited state. Based on the results obtained in Table 8, it can

be concluded that the electron-acceptor’s substituents have

a greater infuence on the spectral properties of the com-

pounds tested due to the higher value of the proportionality

constant, ρ. On the other hand, properties of the solvents

used have no signifcant efect on the absorption changes

caused by the nature of the substituent. (Values of the pro-

portionality constants for all solvents used are very close).

The infuence of the substituent on the absorption

spectra of carbohydrazones

In addition to the medium in which the substance is dissolved,

the appearance of absorption spectra is also infuenced by

the structure of the molecule, i.e., the distribution of electron

density. In the case of the investigated carbohydrazones, the

appearance of the spectrum depends on the type and position

Computational results

Photon absorption can induce a deformation in the molecu-

lar electronic cloud and can cause a partial shift of electrons

1 3

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from one part of the molecule to another, known as intramo-

lecular charge transfer (ICT). An efcient way to estimate a

character of excitation is by calculating Tozer’s Λ diagnostic

index. The Λ index represents the spatial overlap between

the occupied and virtual orbitals involved in the selected

excitation and can have a value between 0 and 1, with 1

indicating a perfect overlap between orbitals (no intermo-

lecular charge transfer) and value of 0 indicating complete

separation of occupied and virtual orbitals. Based on exten-

sive benchmark calculations (Peach et al. 2008; Peach et al.

2009; Peach and Tozer 2009), values of Λ > 0.3 represent

localized, short-range transition.

agreement between calculated and experimentally observed

results. Most of the compounds have bathochromic shifts

relative to the unsubstituted compound except compound 8.

Also, compound 2 in its most stable E isomer form shows

a signifcant hypsochromic shift (around 17 nm) in both sol-

vents due to the formation of a strong intramolecular hydro-

gen bond. In the Z isomer of compound 2, no intramolecular

hydrogen bond can be formed due to steric constraints, and,

as expected, there is a bathochromic shift when compared

to compound 1. Also, TD-DFT calculations were able to

correctly predict the hypsochromic shift in methanol, when

compared to DMSO, for both isomers of all investigated

compounds, and this is in line with experimentally observed

results.

Results of the calculations of Λ index and ICT indices,

charge-transfer distance (D_CT) and amount of transferred

charge (Q_CT), for Z isomers of all investigated compounds,

are shown in Table 9. All investigated compounds, except

compounds with nitro substituent (compounds 8–10), have

large Λ values, indicating a small amount of ICT between

the ground and the excited states. This is confrmed by cal-

culations of the amount of transferred charge (Q_CT) index

which is in the range between 0.333 e⁻and 0.552 e⁻. Transi-

tions in compounds with a nitro group (compounds 8–10)

show somewhat more pronounced ICT character; Λ values

between 0.52 and 0.56 and Q_CTvalues between 0.573 e⁻and

0.724 e⁻(Table 9).

TD-DFT calculations have shown that, due to its planar

geometries, E isomers have frst absorption maxima at lower

energies than Z isomers. Again, compound 2 is the excep-

tion; the frst absorption maximum for E isomer is 13.49

and 13.90 nm lower in DMSO and methanol than for the Z

isomer (Tables S3–S6).

From Tables S3–S6, it can be seen that in Z and E iso-

mers of almost all investigated compounds [except 2 (E

form), 8 and 9 (Z form)] the main contribution to the frst

excited state comes from HOMO–LUMO single-particle

excitation. In order to visualize the nature of this excitation,

the orbitals with the highest contribution were localized

using the NBO localization procedure and are shown in

Fig. 8 for the most stable isomer of every investigated com-

pound. All the HOMO orbitals (HOMO-1 for compound 2,

E form) are nonbonding in nature, mainly acting as electron

pair on the oxygen atom. All the LUMO orbitals (LUMO

+1 for compounds 8 and 9 (Z form)) are π anti-bonding in

nature. This is in agreement with our previous statement

that n→π* transitions are responsible for the frst absorp-

tion maxima.

In Fig. 6, the diference between electronic densities in

the ground and excited states (top part) and positions of

charge loss and charge gain barycenters (bottom part) are

shown. For example, in the unsubstituted compound, during

excitation, there is a charge transfer of 0.530 e⁻from phenyl

group to the carbohydrazide moiety with charge-transfer dis-

tance (D_CT) at 2.067 Ǻ. The similar ICT process is observed

in compounds 6, 7, 9, 11 and 14–18 (D_CTvalues between

1.773 Ǻ and 2.449 Ǻ). In compound 8, the larger amount of

charge (0.618 e⁻) is transferred across the longer distance

(2.293 Å) from the nitro group in the ortho position to the

carbohydrazide part of the molecule. In other compounds,

no signifcant ICT pr ocesses can be observed due to short

D_CTvalues (Table 9, Fig. 6).

Conclusion

In order to further support experimental fndings and con-

frmation of n→π* nature of frst transition state, TD-DFT

calculations with B3LYP/6-311G(d,p) method of Z and E

isomers of all synthesized molecules were performed. The

calculations were done in two diferent solvents: methanol

(polar protic) and DMSO (polar aprotic). For comparison

purposes, Fig. 7 shows the experimental and theoretical UV

spectra of compound 17, both in DMSO and in methanol

as a solvent. The summary of the calculation results is pre-

sented in Tables S3–S6.

Eighteen monocarbohydrazones were synthesized and char-

acterized using diferent methods. The purity of the com-

pounds made was confrmed using NMR ¹³C, ¹H, IR and ele-

mental analysis. Giving the fact that the presence of imino

group allows E/Z isomerization, some of the synthesized

compounds were presented as a mixture of both isomers

and their stereochemistry was established using 2D NMR

techniques. Obtained results showed that E form dominates

in DMSO solution.

UV spectra of the tested derivatives were recorded in the

range from 200 to 400 nm in nineteen solvents of diferent

properties. It was assumed and confrmed that the analyzed

maxima came as a result of n→π* transition in molecules.

Due to the large values of Λ index (Table 9 ), we expected

a hybrid functional to perform well (Peach et al. 2008; Peach

et al. 2009), and, in general, there is a reasonably good

1 3

Chemical Papers

1 3

Chemical Papers

◂Fig. 6 ICT processes in Z isomers of compounds 1–18, top images—

diference between densities in excited and ground states (red and

blue—density increase and decrease upon transition, respectively);

bottom images—positions of barycenters for charge loss (cyan circle)

and charge gain (violet circle) upon transition

In order to further support experimental fndings and con-

frmation of n→π* nature of frst transition state, TD-DFT

calculations with B3LYP/6-311G(d,p) calculations of Z and

E isomers of all synthesized molecules were performed in

two diferent solvents: methanol (polar protic) and DMSO

(polar aprotic). In general, there was a reasonably good

agreement between calculated and experimentally observed

results. Most of the compounds had a bathochromic shift

relative to the unsubstituted compound. Also, TD-DFT cal-

culations were able to correctly predict the hypsochromic

shift in methanol, when compared to DMSO, for both iso-

mers of all investigated compounds, and this is in line with

experimentally observed results.

The efects of specifc and nonspecifc interactions on

the UV absorption maxima shifts of the monocarbohydra-

zones were studied using two models, Kamlet–Taft’s and

Catalan’s. In addition to this, correlations of the absorption

maxima with Hansen’s solubility parameters were made in

order to obtain additional information about the interactions

that occur between the investigated compounds and the sur-

rounding medium. Results obtained by correlating diferent

empirical parameters of the solvents used with absorption

frequencies of the compounds tested show that nonspecifc

interactions (polarizability and dipolarity) are more domi-

nant and have a greater infuence on maxima shifting of the

monocarbohydrazones. Slightly smaller infuence has acid-

ity, while the smallest infuence has the basicity of the sur-

rounding medium.

In Z and E isomers of almost all investigated compounds,

the main contribution to the frst excited state came from

HOMO–LUMO single particle excitation. All the HOMO

orbitals are nonbonding in nature, mainly acting as electron

pair on the oxygen atom. All the LUMO orbitals are π anti-

bonding in nature. This is in agreement with our previous

statement that n→π* transitions are responsible for the frst

absorption maxima.

The infuence of the structure on the absorption max-

ima shifts was interpreted using Hammett’s equation. Two

dependencies were obtained, one for electron-donor sub-

stituents and one for electron-acceptor substituents. Based

on the results obtained, electron-acceptor substituents have

a greater infuence on the spectral properties of the com-

pounds tested due to the higher value of the proportionality

constant, ρ.

Results of the calculations of ICT indices, charge-transfer

distance (D_CT) and amount of transferred charge (Q_CT), for

Z isomers of all investigated compounds showed that in

the unsubstituted compound, during excitation, there was

a charge transfer of 0.530 e⁻from phenyl group to the car-

bohydrazide moiety. A similar ICT process was observed in

compounds 6, 7, 9, 11 and 14–18. In compound 8, the larger

amount of charge (0.618 e⁻) is transferred across the longer

distance (2.293 Å) from the nitro group in the ortho position

to the carbohydrazide part of the molecule. In other com-

pounds, no signifcant ICT processes could not be observed

due to short D_CTvalues.

Energies obtained from ab initio calculations at MP2/6-

311G(d,p) level of theory have shown that Z isomer is

2.38–5.84 kcal/mol more stable for all compounds, except

for compound 2 where E confguration shows higher sta-

bility due to the formation of the intermolecular hydrogen

bond.

Fig. 7 Experimental and theoretical UV spectra of compound 17 in DMSO and methanol

1 3

Chemical Papers

1 3

Chemical Papers

Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA,

Cheeseman JR, Scalmani G, Barone V, Petersson GA, Nakat-

suji H, Li X, Caricato M, Marenich AV, Bloino J, Janesko BG,

Gomperts R, Mennucci B, Hratchian HP, Ortiz JV, Izmaylov

AF, Sonnenberg JL, Williams-Young D, Ding F, Lipparini F,

Egidi F, Goings J, Peng B, Petrone A, Henderson T, Ranas-

inghe D, Zakrzewski VG, Gao J, Rega N, Zheng G, Liang W,

Hada M, Ehara M, Toyota K, Fukuda R, Hasegawa J, Ishida M,

Nakajima T, Honda Y, Kitao O, Nakai H, Vreven T, Throssell K,

Montgomery JA, Peralta JE, Ogliaro F, Bearpark MJ, Heyd JJ,

Brothers EN, Kudin KN, Staroverov VN, Keith TA, Kobayashi

R, Normand J, Raghavachari K, Rendell AP, Burant JC, Iyengar

SS, Tomasi J, Cossi M, Millam JM, Klene M, Adamo C, Cammi

R, Ochterski JW, Martin RL, Morokuma K, Farkas O, Foresman

JB, Fox DJ (2016) Gaussian 16, Revision B.01, Gaussian, Inc.,

Wallingford CT

Fig. 8 Frontier orbitals with the highest CI expansion coefcients,

localized by NBO localization procedure for the most stable isomers

of all investigated compounds

◂

Acknowledgements This work was supported by the Ministry of Edu-

cation, Science and Technological Development of the Republic of

Serbia (Project 172013).

Compliance with ethical standards

Conflict of interest The authors declare that they have no confict of

interest.

Gangarapu K, Manda S, Jallapally A, Thota S, Karki SS, Balzarini J,

De Clercq E, Tokuda H (2014) Synthesis of thiocarbohydrazide

and carbohydrazide derivatives as possible biologically active

agents. Med Chem Res 23:1046–1056. https://doi.org/10.1007/

s00044-013-0684-3

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Synthesis, solvent interactions and computational study of monocarbohydrazones

DOI: 10.1007/s11696-020-01106-4

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Full text of DOI:10.1007/s11696-020-01106-4

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