Synthesis, characterization, tautomerism and theoretical study of some new Schiff base derivatives

Article abstract of DOI:10.1016/j.saa.2011.04.089

New Schiff base derivatives were prepared by the condensation of 5-chloro and 5-bromo salicylaldehyde with bis(o-aminophenol)ethers. Five bis(o-nitrophenol)ether compounds were synthesized using some ditosylate, 1,3-dibromopropane and 1,4-dibromobuthane w

Full text of DOI:10.1016/j.saa.2011.04.089

Spectrochimica Acta Part A 79 (2011) 1573–1583
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization, tautomerism and theoretical study of some new
Schiff base derivatives
Güls¸ en Türkog˘lua, Halil Berbera,∗, Hakan Dala, Cemil Ög˘retirb
a Anadolu University, Faculty of Science, Chemistry Department, 26470 Eskis¸ehir, Turkey
b Eskis¸ehir Osmangazi University, Faculty Arts and Sciences, Chemistry Department, 26040 Eskis¸ehir, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
New Schiff base derivatives were prepared by the condensation of 5-chloro and 5-bromo salicylaldehyde
with bis(o-aminophenol)ethers. Five bis(o-nitrophenol)ether compounds were synthesized using some
ditosylate, 1,3-dibromopropane and 1,4-dibromobuthane with o-nitrophenol. These compounds were
reduced to bis(o-aminophenol)ethers. The products have been characterized by elemental analysis, FTIR,
1H, 13C NMR, HETCOR and HMBC spectroscopic techniques. The tautomerisms of all of the Schiff bases
compounds were determined in DMSO, CHCl3, C2H5OH and C6H12 solvents and in both acidic and basic
media using the UV–vis spectrophotometric method. The heat of formation (ꢀHf), enthalpy (ꢀH), entropy
(ꢀS), Gibbs free energy (ꢀGf and ꢀG), stable isomers, conformations and tautomers of the synthesized
compounds are calculated using the MOPAC2009 (PM6) program.
Received 25 February 2011
Received in revised form 30 March 2011
Accepted 10 April 2011
This paper is dedicated to Dear Professor
Cemil Ög˘retir.
Keywords:
Schiff basel
© 2011 Elsevier B.V. All rights reserved.
Synthesis
Characterization
Tautomerism
Theoretical calculation
PM6 method
1. Introduction
the ease of formation and remarkable versatility, and therefore
they have played an important role in the development of coor-
The development of the so-called Schiff base compounds has
attracted a lot of interest in the fields of coordination chem-
istry and material sciences [1,2]. Schiff bases that have a solvent
dependent UV–vis spectrum (solvatochromicity) can be suit-
able NLO (non linear optical active) materials [3]. The Schiff
base can accommodate different metal centers involving vari-
ous coordination modes thereby allowing successful synthesis of
homo and hetero metallic complexes with varied stereochemistry
[4].
Schiff bases are important in diverse field chemistry owing to
their biological activity [5]. Apart from the biological activity, pho-
tochromism is another characteristic of these materials leading to
its application in various areas, such as the control and measure-
ment of radiation intensity, display systems and optical computers
[6].
dination chemistry as they readily form stable complexes with
most of the transition metals [10]. Symmetrical diimines and
their metal complexes have been used as models for biological
systems for their antimicrobial and anticancer activities [11,12].
They have also been used in the catalytic reactions [13] and
oxidation reactions [14,15]. Additionally, they have material prop-
erties and analytical applications such as ion selective electrodes
[16].
The proton transfer equilibrium in 2-hydroxy Schiff bases in
solution and solid state has been investigated using mass spec-
tra [17], NMR [18–22], UV–vis [23–27] and X-ray crystallography
[28–30]. Schiff bases with OH group in ortho position to the
amino group are of interest mainly due to the existence of either
O–H. . .. . .N or O. . ...N–H type of hydrogen bond and tautomerism
between enol-imine and keto–amine form. In these compounds,
short hydrogen bonds between the OH group in ortho position to
the imino group and the imine nitrogen are due to stereochem-
istry.
Some crown ether-containing ortho hydroxylated Schiff bases
have been synthesized and their complexation properties with
transition metal cations have been investigated [7–9]. The Schiff
base ligands are one of the most widely used ligands due to
In this study, we synthesized new Schiff bases (Fig. 1) and
investigated using elemental analysis, FTIR, 1H, 13C NMR, HET-
COR and HMBC spectroscopic techniques [31]. Then the tautomers
of all of the Schiff bases compounds were determined using the
UV–vis spectrophotometric method. Conformations and tautomers
∗
Corresponding author: Tel.: +90 222 335 05 80x4827; fax: +90 222 320 49 10.
E-mail address: hlberber@anadolu.edu.tr (H. Berber).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.04.089

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G. Türkog˘lu et al. / Spectrochimica Acta Part A 79 (2011) 1573–1583
of the synthesized compounds are calculated using the MOPAC2009
(PM6) program.
2.3. Synthesis of compound (1)
1,3-Bis(o-aminophenoxy)-3-oxopropane (0.50 g, 1.9 mmol),
was dissolved completely by heating in CH3OH (25 mL). This
solution was added dropwise to
a stirred solution of 5-
2. Experimental
chlorosalicylaldehyde (0.606 g, 3.8 mmol) in CH3OH (25 mL)
over a period of 1 h. Compound (1) was obtained as a bright orange
solid. It was crystallized from CH3OH:THF (tetrahydrofuran) (1:1)
as a bright orange solid. Rf = 0.72 (THF:n-hexane (1:2))
2.1. Reagents and materials
Chemicals used were 2-nitrophenol, diethyleneglycol dichlo-
ride,
triethyleneglycol
dichloride,
5-chlorosalicylaldeyde,
5-bromosalicylaldeyde, hydrazine hydrate (80%) and palla-
dium/carbon (Pd/C) (5%). Solvents pyridine, ethanol (99%) and
dimethylformamide (DMF) were dried by standard methods prior
to use.
2.4. Synthesis of compound (2)
Compound (2) was prepared according to the compound
(1). This reaction used 1,3-bis(o-aminophenoxy)-3-oxopropane
(0.50 g, 1.9 mmol), 5-bromosalicylaldehyde (0.778 g, 3.8 mmol) and
50 mL methanol. It was crystallized from CH3OH:THF (1:1) as an
orange solid. Rf = 0.74 (THF:n-hexane (1:2)).
Carbon, nitrogen and hydrogen analysis were performed on a
VarioEL III CHNS Elemental Analyzer. Melting points were mea-
sured on a Gallenkamp apparatus using a capillary tube. 1H
NMR, 13C NMR, spectra were obtained on a Bruker DPX FT-NMR
(500 MHz) spectrometer (SiMe4 as internal Standard and 85%
H3PO4 as an external Standard). The spectrometer was equipped
with a 5 mm PABBO BB-inverse gradient probe. The concentration
of the solute compounds was 150 mg in 1.0 mL CDCl3 and DMSO-
d6. FTIR spectra were recorded on a Perkin Elmer Spectrum 100
Spectrometer in KBr discs and were reported in cm−1 units. The
UV–visible spectra were measured using a SHIMADZU UV2101 Pc
series spectrometer.
2.5. Synthesis of compound (3)
Compound (3) was prepared according to the compound (1).
This reaction used 1,4-bis(o-aminophenoxy)-4-oxobutane (0.025 g,
0.159 mmol), 5-chlorosalicylaldehyde (0.0217 g, 0.319 mmol) and
50 mL methanol. It was crystallized from CH3OH:THF (1:1) as a
bright yellow-orange solid. Rf = 0.69 (THF:n-hexane (1:2)).
2.6. Synthesis of compound (4)
2.2. Synthetic procedures
Compound (4) was prepared according to the compound
(1). This reaction used 1,5-bis(o-aminophenoxy)-3-oxopentane
(0.40 g, 1.38 mmol), 5-chlorosalicylaldehyde (0.434 g, 2.77 mmol)
and 50 mL methanol. It was crystallized from CH3OH:THF (1:1) as
a bright orange solid. Rf = 0.62 (THF:n-hexane (1:2)).
Compounds were prepared according to basic synthesis
procedures (Fig. 1). Bis(o-nitrophenol)ether and bis(o-
aminophenol)ether compounds were prepared according to
the published procedure [32].
Fig. 1. General procedure for synthesized compounds.

G. Türkog˘lu et al. / Spectrochimica Acta Part A 79 (2011) 1573–1583
1575
Table 1
Experimental and analytical data for synthesized compounds.
Compounds no
Empiric formula
MW (g/mol)
Yield (%)
m.p. (◦C)
Calculated (found) %
C
H
N
1
2
3
4
5
C29H24Cl2N2O4
C29H24Br2N2O4
C30H26Cl2N2O4
C30H26Cl2N2O5
535.42
624.32
549.44
565.44
609.50
98
95
60
68
84
178
178
227–229
150–152
129
65.76 (65.05)
55.79 (56.57)
65.58 (66.46)
63.72 (64.32)
63.06 (63.63)
4.60 (4.52)
3.87 (3.63)
4.77 (4.25)
4.63 (4.55)
4.96 (5.00)
5.00 (5.23)
4.49 (4.63)
5.10 (5.40)
4.95 (5.53)
4.60 (4.86)
C
32H30Cl2N2O6
Table 2
Selected FTIR data for synthesized compounds (ꢁ, cm−1).
Compounds no
ꢁ(C–H) aromatic
ꢁ(C–H) aliphatic
ꢁ(C C) aromatic
ꢁ(C–O–C) aromatic
ꢁ(C–O–C) aliphatic
ꢁ(O–H)
ꢁ(C N)
1
2
3
4
5
3064
3061
3065
3079–3032
3060–3027
2963–2884
2964–2884
2952–2875
2953–2874
2915–2873
1590–1478
1590–1474
1589–1478
1592–1480
1590–1481
1282–1252
1281–1252
1279–1252
1297–1254
1283–1257
–
–
–
3436–2746
3435–2747
3441–2740
3438–2739
3435–2743
1619
1617
1614
1620
1619
1145–1091
1179–1091
Table 3
1H NMR data for synthesized molecules.
.
1H NMR data
H-type
ı (ppm)/J (Hz)
1a
2a
3b
4a
5a
Ha
Hb
Hc
Hd
7.23 (m, 1H)c
7.24 (m, 1H)
7.45 (dd, 1H)
[3Ja-b = 7.87]
[4Ja-c = 1.38]
7.03 (t, 1H)
7.21 (m, 2H)
7.01 (m, 2H)
7.21 (m, 2H)
7.01 (m, 2H)
7.23 (m, 2H)
7.01 (t, 1H)
7.00 (td, 1H)
[3Jb-c,a = 7.73]
[4Jb-d = 1,09]
7.24 (m, 1H)
7.01 (td, 1H)
[3JHb-Hc,a = 7.74]
[4JHb-Hd = 0.97]
7.23 (m, 2H)
[3Jb-c,a = 7.64]
[3Jb-c,a = 7.49]
7.23 (m, 1H)
7.25 (td, 1H)
[3Jc-b,d = 8.46]
[4Jc-a = 1.38[
7.13 (d, 1H)
[3Jd-c = 7.66]
7.06 (d, 1H)
7.06 (d, 1H)
6.96 (dd, 1H)
[3JHd-Hc = 8.30]
[4JHd-Hb = 0.78]
7,34 (d, 1H)
[3Jd-c = 8.54]
[3Jd-c = 7.69]
He
Hf
7,32 (m, 1H)
7.32 (m, 1H)
7,48 (d, 1H)
[3Je-g = 2, 41]
7.44 (dd, 1H)
[3Jg-h = 8.77]
[4Jg-e = 2.46]
6.92 (d, 1H)
[3Jh-g = 8.74]
4.30 (t, 2H)
7,68 (d, 1H)
[3Je-g = 2, 69]
7.40 (dd, 1H)
[3Jg-h = 8.83]
[4Jg-e = 2.69]
6.94 (d, 1H)
[3Jh-g = 8.85]
4.15 (s, 2H)
7,30 (d, 1H)
[3JHe-Hg = 2, 57]
7.25 (dd, 1H)
[3JHg-Hh = 8.83]
[4JHg-He = 2.67]
6.89 (d, 1H)
[3JHe-Hg = 2, 58]
7.26 (d, 1H)
[3JHg-Hh = 8.81]
[4JHg-He = 2.56]
6.92 (d, 1H)
Hg
Hh
6.98 (d, 1H)
[3Jh-g = 8.58]
4.33 (t, 2H)
[3Jk-l = 5.87]
[3JHh-Hg = 8.81]
4.24 (t, 2H)
[3JHh-Hg = 8.81]
4.18 (tt, 2H)
[3Jk-l = 5.88]
[3JHk-Hl = 4.74]
[3JHk-Hl = 4.68]
[2JHk-Hl,k = 25.29]
ꢀ
Hi
2.39 (m, 2H)
2.40 (m, 2H)
1.98 (m, 2H)
4.02 (t, 2H)
3.91 (tt, 2H)
[3Jl-k = 5.82]
[3Jl-k = 5.88]
[3JHl-Hk = 4.74]
[3JHl-Hk = 4.86]
[2JHl-Hk,.l = 24.14]
ꢀ
Hj
–CH
–OH
–
–
–
–
3.78 (s, 2H)
8.70 (s, 1H)
13.80 (s, 1H)
8.62 (s, 1H)
14.00 (s, 1H)
8.62 (s, 1H)
14.10 (s, 1H)
9.00 (s, 1H)
14.10 (s, 1H)
8.60 (s, 1H)
13.80 (s, 1H)
a
1H NMR data in CDCl3.
1H NMR data in DMSO-d6.
b
c
s = singlet, d = doublet, dd = doublet of doublet, t = triplet, tt = triplet of triplet, td = triplet of doublet, m = multiplets.

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G. Türkog˘lu et al. / Spectrochimica Acta Part A 79 (2011) 1573–1583
Table 4
13C NMR data for synthesized molecules.
C-type
13C NMR data ı (ppm)
1a
2a
3b
4a
5a
C1
C2
C3
C4
C5
C6
C7
C8
152.40
136.34
120.25
121.11
128.57
113.33
118.94
159.97
119.04
132.58
123.23
130.83
160.25
64.96
152.40
136.30
119.39
121.11
128.60
113.34
120.90
159.85
119.03
135.36
110.08
133.83
160.73
64.95
152.45
136.28
120.14
121.12
128.58
113.43
118.98
159.80
119.32
133.42
120.23
130.80
160.78
65.12
152.29
136.58
119.92
121.32
128.33
113.46
120.28
160.10
118.85
132.47
123.16
130.89
160.73
68.60
152.26
136.45
120.31
121.27
128.29
113.32
118.85
160.13
120.31
132.50
123.17
130.95
160.94
68.40
C9
C10
C11
C12
C13
C14
C15
C16
29.37
–
29.36
–
29.35
–
70.02
–
69.63
71.03
a
13C NMR data in CDCl3.
b
13C NMR data in DMSO-d6.
2.7. Synthesis of compound (5)
absorption usually appears as a broad band in the IR spectrum.
The ꢁ(C N) absorption bands are observed at 1620–1614 cm−1
region for all of the compounds. The ꢁ(C–O) and ꢁ(C–O, aromatic
ethereal) vibrations bands overlap each other in the all com-
pounds.
Compound (5) was prepared according to the compound
(1). This reaction used 1,8-bis(o-aminophenoxy)-3,6-dioxooctane
(0.50 g, 1.5 mmol), 5-chlorosalicylaldehyde (0.471 g, 3.0 mmol) and
50 mL methanol. It was crystallized from CH3OH:THF (1:1) as an
orange solid. Rf = 0.63 (THF:n-hexane (1:2)).
3.2.2. NMR spectra
All of the 13C NMR and 1H NMR assignments have been writ-
ten on the 1H NMR and 13C NMR spectra (Figs. 2 and 3). All of
the data shows that of the compounds have symmetric structures
in the solution. The 1H NMR data and coupling constant for the
new Schiff bases are listed in Table 3. The broad signal around
ı = 13.80–14.10 ppm are assigned to the protons of the hydroxyl
groups. This peak is due to hydrogen bonded phenolic protons and
the integration is generally less than 2.0 due to this intramolec-
ular hydrogen bonding. Signals for the methine protons of the
characteristic azomethine group for Schiff bases, –N C(H)– were
observed between 9.0 and 8.6 ppm. In the region of 7.48–6.8 ppm
chemical shifts were assigned for hydrogen of the aromatic ring.
The alkyl protons O–CH2–CH2–O were observed between 4.24
and 3.77 ppm. The 1H NMR data for all the compounds shows
the tautomeric equilibrium favours the phenol-imine in solution
(ı = 13.80–14.10 ppm, singlet for OH; ı = 9.0–8.60 ppm, singlet for
–N C(H)–).
3. Result and discussion
3.1. Synthesis
The structures of the Schiff bases have been characterized by
elemental analysis, 1H, 13C NMR and FTIR. All of these new com-
pounds gave spectroscopic and analytical data in Tables 1–4. The
structure of the Schiff bases have been characterized by elemen-
tal analysis. The new five compounds gave yields, melting points
(m.p.) and elemental analysis data of calculated and found in
Table 1.
3.2. Spectroscopy
3.2.1. IR spectra
Selected FTIR frequencies of various diagnostic bands of com-
pounds are given in Table 2. The IR spectra of the Schiff bases
exhibit various bands in the 250–4000 cm−1 region. All of the
compounds (1–5) exhibit two medium intensity absorption sig-
nals at 3079–3061 and 3060–3027 cm−1 attributed to asymmetric
and symmetric stretching vibrations of the Ar–H groups. The O–H
stretching frequency of the all compounds is expected in the
3463–3433 cm−1 region, however, this frequency is generally dis-
placed to the 2757–2723 cm−1 region due to the internal hydrogen
The 13C NMR data for the new Schiff bases are listed in Table 4.
Aliphatic carbon atoms (O–CH2–CH2–O): ı = 71.01–64.95 ppm for
compounds, aromatic carbons were observed between 152.36 and
110.08 ppm.Assignments of the protonated carbons were made by
HETCOR using delay values which correspond to 1J(C,H). As an
example, only the HETCOR spectrum of compound (1) is depicted
in Fig. 4. The C1 carbon atom adjacent to the more electronega-
tive oxygen atom of the aliphatic ring is shifted further downfield
when compared to the neighbouring C6 atom. In addition, C5 and C4
atoms are more shielded than the the others. On the other hand, the
aromatic carbons were also determined using delays in two dimen-
sional HETCOR and HMBC experiments to emphasize the long range
coupling either 2J(C,H), 3J(C,H) or 4J(C,H) between the carbons and
protons (Tables 3 and 4). The absence of non-protonated carbon
atoms (C1, C2, C7, C8, and C11) in the HETCOR have supported
the assignments, C1: at ı = 152.40 ppm, C2: ı = 136.30 ppm, C7:
ı = 118.94 ppm, C8: ı = 159.97 ppm, C11: ı = 123.23 ppm for com-
pound (1). Others carbon atoms (C3, C4, C5, C6, C9, C10 and C12)
bridge OH. . .. . .
ing frequency are observed 3441–3435 cm−1, internal hydrogen
bridge OH. . .. . . C 2747–2739 cm−1 in accordance with the lit-
N C [33]. All of the compounds (1–5) O–H stretch-
N
erature. As the hydrogen bond becomes stronger, the bandwidth
increases, and this band is not always detected. Hydrogen bonds
in these Schiff bases are usually very strong. These compounds
are relatively planar with adequate intramolecular distance that
favours intramolecular hydrogen bond formation [34]. Electron-
donating groups on the phenolic ring increase the electron density
on the hydroxyl oxygen making the H–O bond stronger and the

G. Türkog˘lu et al. / Spectrochimica Acta Part A 79 (2011) 1573–1583
1577
Fig. 2. (a) 1H NMR spectrum of compound (1), (b) The CH2, OCH2 groups region (4.40–2.30 ppm) and the region aromatic protons (6.80–7.40 ppm).
have been assigned respectively, according to the HMBC and HET-
These bands are due to ␲–␲* transitions. In polar solvents (DMSO,
COR spectrum for compound (1).
C2H5OH and CHCl3), one additional band emerges at approximately
450 nm (n–␲), which has logically been linked with the shift of
the tautomeric equilibrium to the keto–amine form. There is a
decrease in imino nitrogen basicity followed by a weakening of
the intramolecular hydrogen bond (O–H. . .. . .N) and a decreased
tendency of the tautomeric inter conversion to keto–amine [34].
The UV–visible spectra of compounds (1–5) were studied in polar
and non-polar solvents both in acidic (CF3COOH) and basic (Et3N)
media. The parameters of the spectra for all of the Schiff bases in
polar and non-polar solvents both in acidic and basic media are
3.3. Tautomerism
In solutions, the tautomerism depends on the solvent polarity
and the ability of the solvents to form hydrogen bonds. The Schiff
bases show absorption in the range greater than 400 nm in polar
and nonpolar solvents. Keto–amine tautomeric forms are present
for the compounds 1–5. The spectra measured in non-polar solvent
(C6H12) contain two bands at approximately 280 and 332–380 nm.

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G. Türkog˘lu et al. / Spectrochimica Acta Part A 79 (2011) 1573–1583
Fig. 3. 13C NMR spectrum of compound (1).
listed in Table 5. Fig. 5 shows the UV spectra for compound 1 in
different solvents both in acidic and basic media. The calculated
keto–amine tautomeric equilibrium of all the compounds are given
in Table 6.
imine forms were dominant for all of the compounds. In pure
solvent media DMSO, the ratios of the keto–amine tautomers of
the (1–5) are higher than in C2H5OH, CHCl3 and C6H12. In acidic
solutions CHCl3 and C6H12, keto–amine tautomers (%) all of the
compounds are observed as higher than the DMSO and C2H5OH
solutions. The bathochromic shifts both above and below 400 nm
in all of the solvents studied (DMSO, C2H5OH, CHCl3 and C6H12) do
not depend on solvent polarities for compounds (1–5). The absence
of a keto–amine form in the acidic solutions of CHCl3 and C6H12 may
be explained by the hydrogen bonding to CF3COOH.
In pure solvent media C6H12
, the keto–amine tautomers
were only observed for compound 5. In basic media C6H12, the
keto–amine tautomers (%) were only measured for compound 4.
Interestingly, when acid was added to a non-polar solvent (C6H12),
the keto–amine forms were observed for the compounds 1–5, but
when the acid was added to polar solvent (DMSO), the phenol-
Fig. 4. HETCOR spectrum of compound (1).

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1579
Table 5
The acid and base effects in the different solvents for tautomerism (T = 298 1 ◦C).
Compounds no Solvent ꢂmax. (nm) (Absorbance)
Solvent mediaa Acidic mediab
Basic mediac
1
359 (A = 0.876) 335 (A = 0.583) 360 (A = 0.792)
257 (A = 1.237) 264 (A = 0.910) 274 (0.684)
457 (A = 0.056) 415 (A = 0.029) 363 (A = 0.561)
347 (A = 0.730) 341 (A = 0.259) 262 (A = 0.796)
279 (A = 0.613)
DMSO
C2H5OH
473 (A = 0.021) 418 (A = 0.618) 458 (A = 0.017)
361 (0.807)
270 (A = 0.613)
322 (A = 0.433) 362 (A = 0.537)
280 (A = 3.082)
CHCl3
359 (A = 0.696) 413 (A = 0.487) 360 (A = 0.402)
269 (A = 0.575) 322 (A = 0.446) 267 (A = 0.274)
360 (A = 0.650) 335 (A = 0.273) 360 (A = 0.550)
C6H12
2
DMSO
C2H5OH
275 (A = 0.499)
343 (A = 0.185) 339 (A = 0.045) 366 (A = 0.127)
285 (A = 0.166) 262 (A = 0.860)
264 (A = 1.031)
457 (A = 0.016) 419 (A = 0.536) 458 (A = 0.015)
362 (A = 0.580) 322 (A = 0.383) 362 (A = 0.389)
294 (A = 0.334)
CHCl3
359 (A = 0.375) 417 (A = 0.120) 362 (A = 0.220)
341 (A = 0.089) 268 (A = 0.579)
36 2 (A = 0.406) 334 (A = 0.154) 365 (A = 0.281)
C6H12
DMSO
3
275 (A = 0.297)
279 (A = 0.110)
346 (A = 0.252) 411 (A = 0.084) 553 (A = 0.007)
285 (A = 0.275) 341 (A = 0.128) 364 (A = 0.176)
289 (A = 0.143)
361 (A = 0.667) 421 (A = 0.868) 458 (A = 0.015)
271 (A = 0.527) 323 (A = 0.598) 360 (A = 0.449)
277 (A = 0.218) 278 (A = 2.512)
C2H5OH
CHCl3
458 (A = 0.005) 411 (A = 0.080) 343 (A = 0.109)
356 (A = 0.109) 343 (A = 0.059) 267 (A = 0.085)
285 (A = 0.067)
C6H12
4
361 (A = 0.725) 335 (A = 0.323) 551 (A = 0.037)
272 (A = 0.595) 257 (A = 1.209) 362 (A = 0.668)
555 (A = 0.005) 341 (A = 0.079) 532 (A = 0.011)
DMSO
C2H5OH
342 (A = 0.339)
282 (A = 0.318)
371 (A = 0.229)
555 (A = 0.016) 417 (A = 0.686) 533 (A = 0.011)
359 (A = 0.802) 323 (A = 0.515) 359 (A = 0.611)
270 (A = 0.647)
CHCl3
539 (A = 0.002) 431 (A = 0.059) 356 (A = 0.876)
356 (A = 0.608) 270 (A = 0.029) 277 (A = 0.298)
269 (A = 0.766)
C6H12
5
552 (A = 0.001) 275 (A = 0.545) 359 (A = 0.693)
359 (A = 0.786)
271 (A = 0.665)
460 (A = 0.021) 339 (A = 0.067) 397 (A = 0.204)
356 (A = 0.398) 260 (A = 0.500) 271 (A = 0.343)
280 (A = 0.198)
335 (A = 0.165)
DMSO
C2H5OH
360 (A = 0.730) 415 (A = 0.396) 360 (A = 0.713)
269 (A = 0.601) 320 (A = 0.314) 270 (A = 0.525)
356 (A = 0.525) 356 (A = 0.296) 405 (A = 0.320)
270 (A = 0.444) 311 (A = 0.368) 268 (A = 0.308)
CHCl3
C6H12
a
b
c
Without acid and base.
Acid effects in solvents.
Basic effects in solvents.
Fig. 5. The typical UV–vis spectra of compound 1 (c = 5 × 10−5 mol L−1). (a) Different
solvents effect in neutral media. (b) in acidic media by addition of CF3COOH (1 mL) to
the given solution. (c) in basic media by addition of Et3N (1 mL) to the given solution.
(DMSO
, C2H5OH ——, CHCl3 · · · · ·, C6H12 − · − · − .)

1580
G. Türkog˘lu et al. / Spectrochimica Acta Part A 79 (2011) 1573–1583
Table 6
keto–amine tautomer (%) in solvent, acidic and basic media for the compounds.
Compounds no
Solvent
Keto–amine tautomer, % a
Solvent media
Acidic mediab
Basic mediac
1
DMSO
C2H5OH
CHCl3
56.2
8.4
3.3
–
–
–
–
1.0
–
10.1
58.8
52.2
C6H12
2
3
4
DMSO
C2H5OH
CHCl3
56.6
–
–
58.3
57.4
–
–
4.3
–
–
–
–
C6H12
DMSO
C2H5OH
CHCl3
57.8
–
55.9
6.9
–
71.9
4.7
0.6
–
39.6
80.0
42.3
C6H12
DMSO
C2H5OH
CHCl3
54.9
1.6
2.4
–
–
–
57.1
67.1
–
–
–
C6H12
67.1
5
DMSO
C2H5OH
CHCl3
0.2
5.8
–
–
–
55.6
46.5
56.0
50.7
57.6
–
C6H12
54.2
a
Keto isomer (%) = (A2/A2 + A1) × 100 where, A1 = the absorbance of the phenol-imine isomer (␲–␲*); A2 = the absorbance of the keto–amine isomer (n–␲*).
Acidic media is attained by addition of CF3COOH(∼1 mL) to the given solution (molecules concentration 1 × 10−5 mol L−1).
Basic media is attained by addition of Et3N(∼1 mL) to the given solution (molecules concentration 1 × 10−5 mol L−1).
b
c
(bond lengths, bond angles and dihedral angles) were estimated
by a molecular mechanic program (ChemOffice) [36].
No noticeable increase or decrease in the keto–amine tautomers
(%) were observed by changing the solvent polarities for the com-
ꢀHf, ꢀH, ꢀS, ꢀGf and ꢀG are listed in Table 7. It is observed
that e tautomeric forms of the compounds are more stable than k
tautomeric forms depending on Gibss free energies (ꢀGf) (Table 7).
In theoretical tautomeric equilibrium calculations, e (phenol
forms) of all the studied compounds are more stable than k (keto
forms) (Fig. 6, Table 8).
pounds (1–5).
3.4. Theoretical calculations
The theoretical calculations were carried out by the MOPAC2009
pocket program at Restricted Hartree–Fock level using PM6 semi-
empirical SCF-MO methods [35]. An Intel Pentium Pro. 400 MHz
computer was used. The initial data for geometry optimization
Any meaningful correlation could not be observed between the
tautomeric equilibrium and the solvent polarities (Table 9).
Fig. 6. Tautomeric structures of the compounds used in the theoretical calculations.

Table 7
Thermodynamic parameters of the studied compounds by PM6 method in liquid phase (T = 298 K).
a
a
Compounds no ꢀHf (kcal mol−1
)
ꢀH (cal mol−1
)
ꢀS (kcal mol−1
)
ꢀGf (kcal mol−1
)
ꢀGb
Compounds no ꢀHf (kcal mol−1
)
ꢀH (cal mol−1
)
ꢀS (kcal mol−1
)
ꢀGf (kcal mol−1
)
ꢀGb (kcal mol−1
)
DMSO
DMSO
1e
2e
3e
4e
5e
−64.35221804.085
−42.00422099.692
−70.95023056.370
−106.47723489.021
−151.09925766.653
131.442
132.214
137.216
140.084
153.163
−103.522
−81.404
−17.366
−17.300
−17.834
−18.256
−19.876
1k
2k
3k
4k
5k
−55.96621939.810
−34.10122674.554
−61.16323078.875
−94.92823813.799
−145.89025400.401
131.688
133.072
136.837
140.611
152.594
−95.209
−73.756
−17.303
−16.981
−17.699
−18.088
−20.073
−111.840
−148.222
−196.742
−101.940
−136.830
−191.363
C2H5OH
1e
2e
3e
4e
C2H5OH
1k
2k
3e
4k
−63.65221790.406
−41.29122091.046
−70.27523051.763
−105.70723474.077
−150.43525755.419
131.396
132.170
137.180
140.054
153.121
−102.808
−80.678
−17.366
−17.296
−17.828
−18.262
−19.875
−55.29921932.350
−33.17122670.458
−60.33623071.354
−94.08223812.252
−145.25225395.208
131.647
133.026
136.801
140.579
152.553
−94.530
−72.813
−17.299
−16.971
−17.695
−18.080
−20.066
−111.155
−147.443
−196.065
−101.103
−135.974
−190.713
5e
5k
CHCl3
1e
2e
3e
4e
CHCl3
1k
2k
3k
4k
−58.31121723.786
−35.83522037.117
−65.11123008.303
−99.86723390.856
−145.33825684.354
131.053
131.867
136.875
139.837
152.855
−97.365
−75.131
−17.330
−17.259
−17.781
−18.281
−19.866
−50.29921860.476
−26.27122615.920
−54.12923056.826
−87.75123763.353
−140.36925351.877
131.311
132.677
136.553
140.373
152.273
−89.430
−65.809
−94.822
−129.582
−185.746
−17.270
−16.922
−17.636
−18.068
−20.025
−105.900
−141.538
−190.889
5e
5k
C6H12
1e
2e
3e
4e
C6H12
1k
2k
3k
4k
−51.30921642.261
−28.65021961.493
−58.31322895.935
−92.28923308.134
−138.58225590.157
130.647
131.494
136.321
139.552
152.516
−90.242
−67.835
−98.937
−133.876
−184.032
−17.290
−17.224
−17.728
−18.278
−19.860
−43.95621783.219
−17.67422503.743
−46.25422950.595
−79.73023737.145
−133.93325317.572
130.903
132.264
136.243
140.114
151.952
−82.965
−57.089
−86.854
−121.484
−179.215
−17.226
−16.911
−17.650
−18.017
−19.964
5e
5k
a
ꢀGf = ꢀHf − TꢀS.
b
ꢀG = ꢀH − TꢀS.

1582
G. Türkog˘lu et al. / Spectrochimica Acta Part A 79 (2011) 1573–1583
Table 8
Tautomeric equilibrium constants (KT) by PM6 method in liquid phase.
b
c
d
f
g
Processa
␦ꢀGf
KTf
pKTf
␦ꢀGe
KT
pKT
DMSO
1k-1e
2k-2e
3k-3e
4k-4e
5k-5e
C2H5OH
1k-1e
2k-2e
3k-3e
4k-4e
5k-5e
CHCl3
1k-1e
2k-2e
3k-3e
4k-4e
5k-5e
C6H12
1k-1e
2k-2e
3k-3e
4k-4e
5k-5e
−8.313
−7.647
−9.900
−11.392
−5.379
1.25 × 106
4.06 × 105
1.82 × 107
2.27 × 108
8.80 × 103
−6.097
−5.609
−7.261
−8.355
−3.945
−0.062
−0.319
−0.135
−0.168
0.197
1.111
1.714
1.257
1.327
0.717
−0.046
−0.234
−0.099
−0.123
0.144
−8.278
−7.865
1.18 × 106
5.87 × 105
2.36 × 107
2.58 × 108
8.43 × 103
−6.072
−5.768
−7.373
−8.412
−3.926
−0.067
−0.324
−0.133
−0.182
0.191
1.120
1.728
1.251
1.359
0.724
−0.049
−0.238
−0.097
−0.133
0.140
−10.052
−11.469
−5.352
−7.935
−9.323
6.61 × 105
6.88 × 106
1.33 × 108
5.88 × 108
5.91 × 103
−5.820
−6.838
−8.125
−8.769
−3.772
−0.060
−0.337
−0.144
−0.213
0.159
1.106
1.768
1.276
1.432
0.764
−0.044
−0.248
−0.106
−0.156
0.117
−11.078
−11.956
−5.142
−7.277
−10.747
−12.082
−12.392
−4.817
2.17 × 105
7.62 × 107
7.27 × 108
1.23 × 109
3.41 × 103
−5.337
−7.882
−8.862
−9.089
−3.533
−0.064
−0.313
−0.078
−0.262
0.105
1.115
1.696
1.141
1.556
0.838
−0.047
−0.229
−0.057
−0.192
0.077
a
Process; k form ꢀ e form. Calculated in equality.
b
c
d
e
f
ıꢀGf; ıꢀGf = ꢀGf(e) − ꢀGf(k)
.
KTf; KTf = e(−ıꢀGf/RT). Calculated in equality.
pKT(f); pKT(f) = −log KTf Calculated in equality.
ıꢀG; ıꢀG = ꢀG(e) − ꢀG(k). Calculated in equality.
KT; KT = e(−ıꢀG/RT). Calculated in equality.
g
pKT; pKT = −log KT. Calculated in equality. R = 1.987 × 10−3 kcal mol−1 K ve T = 298 K (the plus sign indicates the stability of keto form).
Table 9
The PM6 and experimental tautomeric equilibrium constants (KT) in different solvents.
Compounds no
Experimental tautomeric equilibrium constants
Calculated tautomeric equilibrium constants
KT(exp.)
ıꢀGf
KTf
pKTf
ıꢀG
KT
pKT
DMSO
1
2
3
4
5
56.20
56.60
57.80
54.90
0.15
−8.313
−7.647
−9.900
−11.392
−5.379
1.25 × 106 −6.097
4.06 × 105 −5.609
1.82 × 107 −7.261
2.27 × 108 −8.355
8.80 × 103 −3.945
−0.062
−0.319
−0.135
−0.168
0.197
1.111
−0.046
−0.234
−0.099
−0.123
0.144
1.714
1.257
1.327
0.717
C2H5OH
1
2
3
4
8.40
–
–
1.60
5.80
−8.278
−7.865
1.18 × 106 −6.072
5.87 × 105 −5.768
2.36 × 107 −7.373
2.58 × 108 −8.412
8.43 × 103 −3.926
−0.067
−0.324
−0.133
−0.182
0.191
1.120
1.728
1.251
1.359
0.724
−0.049
−0.238
−0.097
−0.133
0.140
−10.052
−11.469
−5.352
5
CHCl3
1
2
3
4
5
3.30
–
55.90
2.40
–
−7.935
6.61 × 105 −5.820
−0.06
1.106
1.768
1.276
1.432
0.764
−0.044
−0.248
−0.106
−0.156
0.117
−−9.323
6.88 × 106
-6.838
−0.337
−0.144
−0.213
0.159
−11.078
−11.956
−5.142
1.33 × 108 −8.125
5.88 × 108 −8.769
5.91 × 103 −3.772
C6H12
1
2
3
4
5
–
–
−7.277
−10.747
−12.082
−12.392
−4.817
2.17 × 105 −5.337
7.62 × 107 −7.882
7.27 × 108 −8.862
1.23 × 109 −9.089
3.41 × 103 −3.533
−0.064
−0.313
−0.078
−0.262
0.105
1.115
1.696
1.141
1.556
0.838
−0.047
−0.229
−0.057
−0.192
0.077
6.90
–
54.20
4. Conclusion
media. No meaningful correlation between the experimental and
the theoretical tautomeric results were observed.
The structures of the synthesized compounds in the present
study have been characterized by elemental analysis, FTIR, 1H and
13C NMR spectroscopic techniques. The structures of compounds
synthesized were also determined using the HETCOR and HMBC
spectroscopic techniques.
Acknowledgements
We are grateful to Medicinal Plants and Medicine Research Cen-
ter of Anadolu University Eskis¸ ehir (Turkey) for NMR and 2D NMR
spectrums and to Anadolu University for ChemOffice 2010 pro-
gram. We are also grateful for MOPAC2009 free package program.
The tautomeric equilibrium constants of the compounds were
calculated experimentally and theoretically in different solvent

G. Türkog˘lu et al. / Spectrochimica Acta Part A 79 (2011) 1573–1583
1583
References
[19] S.H. Alarcon, A.C. Olivieri, G.R. Labadie, R.M. Cravero, M. Gonzalez-Sierra, Tetra-
hedron 51 (1995) 4619–4626.
[20] S.H. Alarcon, D. Pagani, J. Bacigalupo, A.C. Olivieri, J. Mol. Struct. 475 (1999)
233–240.
[21] Z. Rozwadowski, T. Dziembowska, A. Filarowski, P.E. Hansen, Magn. Reson.
Chem. 39 (2001) 67–80.
[22] Z. Rozwadowski, W. Schilf, B. Kamienski, Magn. Reson. Chem. 43 (2005)
573–577.
[23] Z. Hayvali, D. Yardimci, Transition Met. Chem. 33 (2008) 421–429.
[24] Z. Hayvali, N. Gunduz, Z. Kilic, E. Weber, Z. Naturforsch 55b (2000) 975–981.
[25] Z. Hayvali, M. Hayvali, Z. Kilic, T. Hokelek, E. Weber, J. Incl. Phenom. Macrocycl.
Chem. 45 (2003) 285–294.
[26] M. Hayvali, Z. Hayvali, Synth. React. Met. Org. Chem. 34 (2004) 713–732.
[27] H. Unver, M. Yildiz, N. Ocak, T.N. Durlu, J. Chem. Crystallogr. 38 (2008) 103–108.
[28] S. Sharif, D.R. Powell, D. Schagen, T. Steiner, M.D. Toney, E. Fogle, H.H. Limbach,
Biochemistry 38 (1999) 311–320.
[29] M. Yildiz, H. Unver, D. Erdener, N. Ocak, A. Erdonmez, T.N. Durlu, Cryst. Res.
Technol. 41 (2006) 600–606.
[1] C.P. Johnson, J.L. Atwood, J.W. Steed, C.B. Bauner, R.D. Rogers, Inorg. Chem. 35
(1996) 2602–2610.
[2] N. Alizadeh, S. Ershad, H. Naeimi, H. Shargi, M. Shamsipur, Pol. J. Chem. 73
(1999) 915–925.
[3] A.A. Alemi, B. Shaabani, Acta Chim. Slov. 47 (2000) 363–369.
[4] H. Naeimi, K. Rabiei, F. Salimi, Dyes Pigments 75 (2007) 294–297.
[5] J. Costamagna, J. Vargas, R. Latorre, A. Alvarado, G. Mena, Coord. Chem. Rev. 119
(1992) 67–88.
[6] A. Elmalı, M. Kabak, E. Kavlakog˘lu, Y. Elerman, T.N. Durlu, J. Mol. Struct. 510
(1999) 207–214.
[7] W. Zeng, J. Li, Z. Mao, Z. Hong, S. Qin, Adv. Synth. Catal. 346 (11) (2004)
1385–1391.
[8] Z. Hayvali, N. Gunduz, Z. Kilic, E. Weber, J. Prakt. Chem. 341 (6) (1999)
568–573.
[9] X. Wei, Z. Mao, J. Li, S. Qin, Synthetic Commun. 34 (2004) 1237–1246.
[10] H. Keypour, P. Arzhangi, N. Rahpeyma, M. Rezaeivala, Y. Elerman, H.R. Khavasi,
Inorg. Chim. Acta 367 (2011) 9–14.
[11] L. Shi, H.M. Ge, S.H. Tan, H.Q. Li, Y.C. Song, H.L. Zhu, R.X. Tan, Eur. J. Med. Chem.
42 (2007) 558–564.
[12] S.M. Abdallah, G.G. Mohamed, M.A. Zayed, M.S. Abou El-Ela, Spectrochim. Acta
Part A 73 (2009) 833–840.
[13] D.M. Boghaei, S. Mohebi, Tetrahedron 58 (2002) 5357–5366.
[14] M.L.P. Santos, A. Faljoni-Alario, A.S. Mangrich, A.M.C. Ferreira, J. Inorg. Biochem.
71 (1–2) (1998) 71–78.
[15] S. Arunachalam, N.P. Priya, C. Jayabalakrishnan, V. Chinnusamy, Spectrochim.
Acta Part A 74 (2009) 591–596.
[16] C. Hazneci, K. Ertekin, B. Yenigul, E. Cetinkaya, Dyes Pigments 62 (2004) 35–41.
[17] S.R. Salman, F.S. Kamounah, Spectrosc. Lett. 35 (2002) 327–335.
[18] J.-C. Zhuo, Magn. Reson. Chem. 37 (1999) 259–268.
[30] J. Ribas, C. Diaz, R. Costa, Y. Journauv, C. Mathoniere, O. Kahn, A. Gleizes, Inorg.
Chem. 29 (1990) 2042–2047.
[31] G. Türkog˘lu, ‘Synthesis of Some Diphenolic Schiff Base Compounds and Their
Structural Characterization’ Master of Science Thesis, Anadolu University, Sci-
ences Institute, Eskis¸ ehir, Turkey, (2007).
[32] J.P. Dutasta, J.P. Declercq, C.E. Calderon, B. Tinant, J. Am. Chem. Soc. 111 (18)
(1989) 7136–7144.
[33] H.H. Freedman, J. Am. Chem. Soc. 83 (1961) 2194–2195.
[34] M. Yıldız, Z. Kılıc¸ , T. Hökelek, J. Mol. Struct. 441 (1998) 1–10.
[35] MOPAC2009, James J. P. Stewart, Stewart Computational Chemistry, Colorado
Springs, CO. USA. http://OpenMOPAC.net (2008).
[36] CS Chemoffice Pro for Microsoft Windows, Cambridge Scientific Computing,
Inc. 875 Massachusetts Avenue, Suite 61, Cambridge, MA 2139, USA.