DFT, FT-IR, FT-Raman and NMR studies of 4-(substituted phenylazo)-3,5- diacetamido-1H-pyrazoles

Article abstract of DOI:10.1016/j.molstruc.2011.02.009

We present a detailed analysis of the structural and vibrational spectra of some novel azo dyes. 2-(Substituted phenylazo)malononitriles were synthesized by the coupling reaction of the diazonium salts, which were prepared with the use of various aniline

Full text of DOI:10.1016/j.molstruc.2011.02.009

Journal of Molecular Structure 993 (2011) 254–258
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Journal of Molecular Structure
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DFT, FT-IR, FT-Raman and NMR studies of 4-(substituted
phenylazo)-3,5-diacetamido-1H-pyrazoles
c
c
d
Selin Kınalı a, Serkan Demirci b, , Zühre Çalıßsır , Mustafa Kurt , Ahmet Ataç
⇑
a Gazi University, Faculty of Arts and Sciences, Department of Chemistry, 06500 Ankara, Turkey
b Ahi Evran University, Faculty of Arts and Sciences, Department of Chemistry, 40100 Kırßsehir, Turkey
c Ahi Evran University, Faculty of Arts and Sciences, Department of Physics, 40100 Kırßsehir, Turkey
d Celal Bayar University, Faculty of Arts and Sciences, Department of Physics, 45043 Manisa, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 4 March 2011
We present a detailed analysis of the structural and vibrational spectra of some novel azo dyes. 2-(Substi-
tuted phenylazo)malononitriles were synthesized by the coupling reaction of the diazonium salts, which
were prepared with the use of various aniline derivatives with malononitrile, and then 4-(substituted
phenylazo)-3,5-diamino-1H-pyrazole azo dyes were obtained via the ring closure of the azo compounds
with hydrazine monohydrate. The experimental and theoretical vibrational spectra of azo dyes were
studied. The structural and spectroscopic analysis of the molecules were carried out by using Becke’s
three-parameters hybrid functional (B3LYP) and density functional harmonic calculations. The 1H nuclear
magnetic resonance (NMR) chemical shifts of the azo dye molecules were calculated using the gauge-
invariant-atomic orbital (GIAO) method. The calculated vibrational wavenumbers and chemical shifts
were compared with the experimental data of the molecules.
Keywords:
Azo dyes
Pyrazole
Vibrational spectra
DFT
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
It has been known for many years that the azo compounds are
the most widely used class of dyes due to their versatile applica-
tion in various fields such as the dyeing of textile fibers, the color-
ing of different materials, colored plastics, biological and medical
studies, and advanced application in organic synthesis [1–3]. Espe-
cially, pyrazoles are important compounds that have many deriva-
tives with wide range properties, such as biological and
pharmacological activities [4–7].
Several studies, such as synthesis [4,8–10], absorption spectra
[10,11], and solvatochromic behavior [12] have been published of
azo dyes. But, a few theoretical studies have been reported for
the molecular structure and vibrational spectra of azo dyes [13–
15].
In this study, some novel 4-(substituted phenylazo)-3,5-diami-
no-1H-pyrazole azo dyes were synthesized and calculated geomet-
ric structure, vibrational spectra and chemical shift. The calculated
vibrational wavenumbers and chemical shifts were compared with
the experimental data of the molecules. Furthermore, we inter-
preted the calculated spectra in terms of total energy distributions
(TED).
2.1. General
All chemicals used for synthesis of the azo dyes were purchased
from Aldrich without further purification. The solvents used were
of spectroscopic grade.
Fourier Transform Infrared (FT-IR) spectra of the 4-(substituted
phenylazo)-3,5-diacetamido-1H-pyrazoles were carried out using
a Thermo Nicolet 6700 spectrometer with Smart Orbit attenuated
total reflection attachment. The FT-Raman spectrums of the sam-
ples were recorded between 50 and 3500 cmÀ1 region on a Bruker
FRA 106/S FT-Raman instrument using 1064 nm excitation from an
Nd: YAG laser. The detector is a liquid nitrogen cooled Ge detector.
Nuclear magnetic resonance (1H NMR) spectra were recorded on a
Bruker-Spectrospin Avance DPX 400 Ultra-Shield in deuterated
chloroform (CDCl3-d1) using tetramethylsilane (TMS) as the inter-
nal reference; chemical shifts were (d) given in ppm. Melting
points were determined on an Barnstead Electrothermal 9200.
2.2. Synthesis of 4-(substituted phenylazo)-3,5-diacetamido-1H-
pyrazoles
2-(Substituted phenylazo)malononitriles and 4-(substituted
phenylazo)-3,5-diamino-1H-pyrazoles were prepared according
to the literature procedures [16–21]. A general preparative proce-
⇑
Corresponding author. Tel.: +90 386 211 45 40; fax: +90 386 211 45 25.
E-mail addresses: sdemirci@ahievran.edu.tr, srkndemirci@gmail.com (S. Demir-
ci).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.02.009

S. Kınalı et al. / Journal of Molecular Structure 993 (2011) 254–258
255
Table 1
dure was described for the preparation of azo dyes 4-(phenylazo)-
The color, yield and melting point of azo dyes.
3,5-diacetamido-1H-pyrazole (PDP) and 4-(4-methylphenylazo)-
3,5-diacetamido-1H-pyrazole (4m-PDP) by Elnagdi and co-workers
[21]. 4-(2-methylphenylazo)-3,5-diacetamido-1H-pyrazole (2m-
PDP) and 4-(3-methylphenylazo)-3,5-diacetamido-1H-pyrazole
(3m-PDP) were prepared in similar manner. The synthesis of 4-
(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles are shown
in Scheme 1. The color, yield and melting point of azo dyes are gi-
ven in Table 1.
Azo dyes
Color
Yield (%)
Melting point (°C)
PDP
Yellow
Dark green
Yellow
95
90
85
65
218–219
163–165
203–204
245–246
2m-PDP
3m-PDP
4m-PDP
Yellow
Table 2
Selected bond distances (Å) and bond angles (°) of azo dyes.
Parameters
B3LYP
PDP
3. Computational details
2m-PDP
3m-PDP
4m-PDP
Bond Lengths (Å)
C1–N14
C7–N15
C7–C8
C7–C9
All calculations were performed using the Gaussian 09 program
package [22] and Gauss-View molecular visualization program
[23]. The molecular structures of azo dyes were optimized by
DFT/B3LYP level with the 6-31G(d) basis set [24]. The optimized
structural were used in the vibrational wavenumber calculation.
The total energy distribution (TED) was calculated by using the
scaled quantum mechanics (SQM) program. 1H NMR chemical shift
values were calculated by the gauge-including atomic orbital
(GIAO)-DFT method at 6-31G(d) level.
1.4137
1.3652
1.4092
1.4365
1.3868
1.3777
1.2777
1.3788
1.0115
–
1.4135
1.3650
1.4092
1.4365
1.3867
1.378
1.2783
1.3786
1.0114
1.5104
–
1.4137
1.3659
1.4089
1.4361
1.3871
1.3778
1.2779
1.3786
1.0115
–
1.4120
1.3662
1.4086
1.4359
1.3871
1.3782
1.2778
1.3784
1.0114
–
C9–N18
C8–N19
N14–N15
N16–N17
N16–H29
C2–C22
C3–C23
C4–C24
–
–
1.5118
–
–
–
1.5097
Bond Angles (°)
C2–C1–N14
C6–C1–N14
C7–C8–N16
C7–C9–N17
C8–C7–N15
C8–N16–H29
C8–N16–N17
C8–N19–C12
C9–C7–N15
C9–N17–N16
C9–N18–C10
4. Result and discussion
120.0043
119.9972
107.9735
107.9403
110.5339
124.8757
113.7664
124.2846
110.5067
103.875
128.2119
123.0916
124.1968
–
119.9972
120.0043
107.9735
107.9403
110.5339
126.0204
107.9592
110.3651
110.5067
107.9138
110.3651
124.1968
124.1968
119.9808
120.0106
–
119.9972
120.0043
107.9735
107.9403
110.5339
124.8616
113.7628
124.3002
110.5067
103.8638
128.2578
123.049
124.1968
–
120.0043
119.9972
107.9735
107.9403
110.5339
126.0204
107.9592
110.3651
110.5067
107.9138
110.3651
124.1968
124.1968
–
4.1. Molecular geometry
The optimized structural parameters of azo dyes calculated by
DFT/B3LYP level with the 6-31G(d) basis set. The calculated param-
eters of azo dyes (PDP, 2m-PDP, 3m-PDP, 4m-PDP) are given in Ta-
ble 2 and the optimized structures with numbering of the atoms of
azo dyes are shown in Fig. 1. The molecules of 4-(substituted
phenylazo)-3,5-diacetamido-1H-pyrazole consist of two ring (phe-
nyl and pyrazole) systems and connected to each other by the azo
group (N@N). The distance of the N14–N15 bond in PDP, 2m-PDP,
3m-PDP and 4m-PDP is 1.2777, 1.2783, 1.2779, and 1.2778 Å,
respectively. Average length of the N14–N15 bond in 4-(substituted
phenylazo)-3,5-diacetamido-1H-pyrazole molecules increases by
0.0259 Å, as compared to diazene (HN@NH) (1.252 Å) [25]. The
lengthened N14–N15 distance of azo dyes is also caused by the con-
jugation with pyrazole ring. The length of the N14–N15 bonds in
2m-PDP, 3m-PDP and 4m-PDP is longer than N14–N15 bonds in
PDP because of steric incidence. As shown in Table 2, the N@N
bond distance decreases from 1.2783 to 1.2778 with substitute
number of azo dye increases from 2 to 4.
C
C
11–C10–O20
13–C12–O21
C1–C2–C22
C3–C2–C22
C2–C3–C23
C4–C3–C23
C3–C4–C24
C5–C4–C24
–
–
–
–
–
–
–
–
120.9886
120.3004
–
–
–
–
120.0249
119.9811
–
–
4.2. Vibrational analysis
Vibrational spectral assignments were performed on the re-
corded FT-IR and FT-Raman spectra based on the theoretically pre-
Scheme 1. Synthesis of 4-(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles.

256
S. Kınalı et al. / Journal of Molecular Structure 993 (2011) 254–258
Fig. 1. The calculated optimized structures of 4-(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles.
dicted wavenumbers by density functional B3LYP/6-31G(d) meth-
od with scaling factor of 0.9613 [24] and are collected in Tables S1–
S4 (Supporting information). The FT-IR spectra of PDP, 2m-PDP,
3m-PDP and 4m-PDP showed a band at 3450–3200 cmÀ1, which
was assigned to the N–H stretching. The calculated wavenumbers
of the N–H stretching are shown at 3500–3300 cmÀ1. The experi-
mental FT-IR spectrum of the azo dyes show a significant differ-
wavenumbers depending on the neighboring group and intermo-
lecular hydrogen bonding.
The vibrational assignments of most of the fundamental vibra-
tion of the studied molecules were straightforward on the basis of
their calculated total energy distribution (TED) values (Tables S1–
S4). In the high wavenumber region, TED calculations show that all
the C–H and N–H stretching vibrations are pure modes. Similar
comparative analyses have been made for the other type of bands.
As seen in tables for TED values, the calculated modes are mixed
with other group modes in different proportions.
ence in the region of the N–H stretching at 3450–3200 cmÀ1
,
compared with the theoretical FT-IR spectrums. In addition, the
experimental wavenumber observed in the FT-IR spectrums at
1702–1684 cmÀ1 are assigned to C@O stretching vibration, which
show small differences with that obtained with the theoretical
FT-IR spectrums. The band of C@O stretching appeared at 1702–
1684 cmÀ1 was observed in all the experimental spectra of the
azo dyes and the band shifted to a lower frequency range com-
pared theoretical FT-IR spectrums. These differences supports the
stronger intermolecular hydrogen bonding interaction between
NH and C@O groups. For all aromatic C–H stretching vibrations
are observed in the region 3100–3000 cmÀ1. The phenyl ring vibra-
tions assigned to the aromatic C–H stretch computed in the range
3100–3000 cmÀ1 shows good agreement with the recorded FT-IR.
PDP, 2m-PDP, 3m-PDP and 4m-PDP azo dyes are compounds
that contain azo groups linked to phenyl and pyrazole ‘‘C’’ atoms.
It is well known that N@N stretching vibration gives strong Raman
band and that these are quite weak in FT-IR [25,26]. The bands ob-
served at 1391–1370 cmÀ1 in the FT-IR (Fig. 2) and at 1402–
1380 cmÀ1 (Fig. 3) in the Raman spectrums are attributed to the
azo stretching vibration of the azo dyes. In theoretical calculation,
corresponding wavenumbers of azo dyes are assigned to 1450–
1428 cmÀ1. Similarly, azo stretching vibration shifted to a lower
4.3. NMR spectra
The molecular structure of azo dyes were optimized, and then
gauge-including atomic orbital (GIAO) 1H NMR chemical shifts cal-
culations of the title compound were carried out by using B3LYP
functional with 6-31G(d) basis sets. Experimental and calculated
chemical shifts of azo dyes are presented in Table 3. The 1H NMR
spectra of PDP, 2m-PDP, 3m-PDP and 4m-PDP measured in
CDCl3-d1. The 1H NMR spectra of PDP showed three broad N–H
peaks at 11.3, 10.8, 9.3 ppm. The 1H NMR spectra of 2m-PDP and
3m-PDP showed two board peaks at 11.3 and 9.4 for N–H proton.
Similarly, the 1H NMR spectra of 4m-PDP showed two board N–H
peak at 11.2 and 9.4.
4.4. Azo-hydrazo tautomerism
4-(Substituted phenylazo)-3,5-diacetamido-1H-pyrazole azo
dyes can exist two possible tautomeric forms, namely the azo (A)
and the hydrazo (B) forms as shown in Scheme 2. The FT-IR and

S. Kınalı et al. / Journal of Molecular Structure 993 (2011) 254–258
257
Fig. 2. The recorded and simulated FT-IR spectrums of PDP (a), 2m-PDP (b), 3m-PDP (c) and 4m-PDP (d).
Fig. 3. The recorded and simulated FT-Raman spectrums of PDP (a), 2m-PDP (b), 3m-PDP (c) and 4m-PDP (d).
Table 3
Experimental and theoretical 1H NMR data of azo dyes.
Sample
H29
H28
H26
7.4
7.4
7.4
7.4
H23
7.4
7.1
–
H22
H25
9.9
7.1
7.0
7.1
H24
9.6
7.1
7.1
–
H27
H35
2.1
2.1
2.0
2.1
H32
2.0
1.9
1.9
1.9
H30
1.8
H34
1.6
H33
1.5
1.5
1.5
1.4
H31
1.4
1.3
1.3
1.4
H36
H37
H38
PDP
Exp.
Th.
11.3
9.9
10.8
9.6
7.3–7.8
7.0
9.3
9.9
2.3
–
–
–
–
–
–
2m-PDP
Exp.
Th.
11.3
10.0
9.4
9.2
7.2–7.6
9.4
9.4
7.1
2.2–2.7
1.9 1.6
2.4
1.8
2.4
2.2
2.2
2.4
2.3
2.2
3m-PDP
Exp.
Th.
11.3
9.9
9.4
9.3
7.2–7.5
9.4
9.4
7.0
2.3
2.3
2.4
1.8
1.9
1.8
1.6
1.7
4m-PDP
Exp.
Th.
11.2
9.9
9.4
9.5
7.2–7.7
7.0
9.4
6.9
2.4
1.7
7.1
FT-Raman spectra of azo dyes showed N@N stretching vibration at
Raman and 1H NMR results suggest that azo dyes are predomi-
nantly in the azo form in CDCl3 and the solid state (Scheme 2A). El-
1391–1370 cmÀ1 and at 1402–1380 cmÀ1, respectively. FT-IR, FT-

258
S. Kınalı et al. / Journal of Molecular Structure 993 (2011) 254–258
Scheme 2. The azo (A) and hydrazo (B) form of 4-(substituted phenylazo)-3,5-diacetamido-1H-pyrazoles.
[6] A.M. Youssef, E.G. Neeland, E.B. Villanueva, M.S. White, I.M. El-Ashmawy, B.
Patrick, A. Klegeris, A.S. Abd-El-Aziz, Bioorg. Med. Chem. 18 (2010) 5685.
[7] M. Li, C.L. Liu, L. Li, H. Yang, Z.N. Li, H. Zhang, Z.M. Li, Pest. Manag. Sci. 66 (2010)
107.
nagdi and co-workers reported that the p-substituted diacetyl
compounds are present in azo form [21].
[8] S. Gupta, A. Sivasubramanian, L.M. Rodrigues, A.P. Esteves, R. Hrdina, A.M.F.
Oliveira-Campos, Dyes Pigments 75 (2007) 82.
5. Conclusion
[9] M.A. Kamboh, I.B. Solangi, S.T.H. Sherazi, S. Memon, J. Hazard. Mater. 172
(2009) 234.
[10] J.H. Choi, J.M. Jeon, M.H. Kim, A.D. Towns, C. Yoon, Color. Technol. 124 (2008)
92.
Theoretical and experimental vibrational, 1H NMR analysis of 4-
(substituted phenylazo)-3,5-diacetamido-1H-pyrazole azo dyes,
for the first time. A comparison of the result of experimental and
theoretical study gave us a full description of the geometry and
vibrational properties of this molecule. Based on calculated energy
differences, the A conformer is found to be most the stable con-
former and the other conformers are predicted the unstable con-
former. The calculated geometric parameters and vibrational
frequencies obtained with density functional theory calculations
(B3LYP/6-31G(d)) method are in good agreement for some bands
with the experimental values obtained for the investigated mole-
cules. The differences between the experimental and the theoreti-
cal spectrums are due in part to the fact that the theoretical
spectrum is obtained in the gas phase, however the experimental
spectrums are measured in the solid phase where it may undergo
intermolecular interactions.
[11] J. Park, J. Koh, Dyes Pigments 82 (2009) 347.
[12] S. Fozooni, A.M. Tikdari, H. Hamidian, H. Khabazzadeh, Arkivoc 14 (2008) 115.
[13] A. Teimouri, A.N. Chermahini, K. Taban, H.A. Dabbagh, Spectrochim. Acta A 72
(2009) 369.
[14] M. Snehalatha, C. Ravikumar, N. Sekar, V.S. Jayakumar, I.H. Joe, J. Raman
Spectrosc. 39 (2008) 928.
[15] A. Teimouri, A.N. Chermahini, M. Emami, Tetrahedron 64 (2008) 11776.
[16] A.S. Shawali, F.M. Abdel Galil, Tetrahedron 27 (1971) 4305.
[17] F.M. Abdel Galil, F.A. Khalifa, T.S. Abdin, Dyes Pigments 12 (1990) 49.
[18] D.D. Agarwal, V.J. Agarwal, J. Indian. Chem. Soc. 68 (1991) 360.
[19] N.V. Maatschappij, Chem. Abstr. 63 (1965) 13278b.
[20] H.Y. Wen, W.I. Jing, Dyes Pigments 29 (1995) 181.
[21] M.H. Elnagdi, E.M. Kandeel, E.M. Zayed, Z.E. Kandil, J. Heterocycl. Chem. 14
(1977) 155.
[22] Gaussian 09, Revision A.1, M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria,
M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G.
Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery
Jr, J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N.
Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant,
S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev,
A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G.
Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, Ö.
Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian Inc.,
Wallingford, CT, 2009.
[23] A. Frish, A.B. Nielsen, A.J. Holder, Gauss View User Manual, Gaussian Inc.,
Pittsburg, PA, 2001.
[24] J.B. Foresman, A.E. Frisch, Exploring Chemistry with Electronic Structure
Methods, second ed., Gaussian Inc., Pittsburgh, PA, 1996.
[25] M. Snehalatha, C. Ravikumar, I.H. Joe, N. Sekar, V.S. Jayakumar, Spectrochim.
Acta A 72 (2009) 654.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2011.02.009.
References
[1] S.A. Ong, K. Uchiyama, D. Inadama, Y. Ishida, K. Yamagiwa, Bioresource
Technol. 101 (2010) 9049.
[2] L. Pereira, R. Pereira, M.F.R. Pereira, F.P. van der Zee, F.J. Cervantes, M.M. Alves,
J. Hazard. Mater. 183 (2010) 931.
[3] B. Neumann, Dyes Pigments 52 (2002) 47.
[4] F. Karcı, F. Karcı, Dyes Pigments 76 (2008) 97.
[26] M. Snehalatha, C. Ravikumar, N. Sekar, V.S. Javakumar, I.H. Joe, J. Raman
Spectrosc. 39 (2008) 928.
[5] M.J. Genin, C. Biles, B.J. Keiser, S.M. Poppe, S.M. Swaney, W.G. Tarpley, Y. Yagi,
D.L. Romero, J. Med. Chem. 43 (2000) 1034.