An experimental and theoretical study on influence of H-bonding on the synthesized azo derivatives structures

Article abstract of DOI:10.1002/jccs.201200170

We have reported a simple and efficient reaction for the synthesis of some new functionalized azo structures which were prepared by electron deficient acetylenic compounds in the presence of triphenylphosphine. The characterization of the synthesized azo compounds has been determined by FTIR, UV-Vis, ¹H NMR, ¹³C NMR andMass spectroscopic techniques. The influence of H-bonding on the products has been shown by different experimental analysis. Also, the regioselectivity of the reaction, tautomerization equilibrium and the stability of products was investigated using DFT calculations at the B3LYP/6-31G level of theory.

Full text of DOI:10.1002/jccs.201200170

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
An Experimental and Theoretical Study on Influence of H-bonding on the Synthesized
Azo Derivatives Structures
Rahebeh Amiri,a,* Mina Haghdadi,b Ashkan Golshani,c Maryam Mohamadian Amiria and
Maryam Barikania
aChemistry Department, Central Tehran Branch, Islamic Azad University, P.O. Box 1465613111, Tehran, Iran
bChemistry Department, Babol Branch, Islamic Azad University, Babol, Iran
cDepartment of Biology, Carleton University, Ottawa, Ontario, Canada
(Received: Mar. 26, 2012; Accepted: Jul. 31, 2012; Published Online: Nov. 2, 2012; DOI: 10.1002/jccs.201200170)
We have reported a simple and efficient reaction for the synthesis of some new functionalized azo struc-
tures which were prepared by electron deficient acetylenic compounds in the presence of triphenylphos-
phine. The characterization of the synthesized azo compounds has been determined by FTIR, UV-Vis, 1H
NMR,13C NMR and Mass spectroscopic techniques. The influence of H-bonding on the products has been
shown by different experimental analysis. Also, the regioselectivity of the reaction, tautomerization equi-
librium and the stability of products was investigated using DFT calculations at the B3LYP/6-31Glevel of
theory.
Keywords: Triphenylphosphine; DFT calculation; Intramolecular hydrogen bonding.
INTRODUCTION
Over the past few years, azo-aromatic compounds
quality and were purchased from Merck and Aldrich and
used without further purification. Melting points were de-
termined on a Buchi SMP-20, melting point apparatus. In-
frared spectra (in KBr pellets) were recorded on a Perkin-
Elmer 1605 FTIR spectrometer. The NMR spectra were re-
corded at 300 (1H) and 75.5 (13C) MHz on a Bruker 300-
AVANCE FT-NMR instrument in CDCl3 using TMS as an
internal reference. The electronic spectra of the products
were recorded on a UV-1601 Shimadzu spectrophotometer
in CHCl3. Mass spectra were recorded on a Finnigan-Matt
8430 spectrometer operating at an ionization potential of
70 eV. Column chromatography was performed using 230-
400 mesh Merck silica gel and mixtures of n-hexane;
CH2Cl2 and EtOAc were used as eluents.
have been widely used as dyes and pigments in a variety of
industrial1-4 and they play an important role in other appli-
cations such as biological reactions.5 Also azobenzene de-
rivatives, which are one of the most extensively studied
groups of photochromic materials, have the potential uses
as photoactive media for information storage and elec-
tro-optic devices.6-10 Apart from practical aspects, which
have the noticeable importance, structure-property rela-
tionships have remained of great interest.11 In the present
work, we have used an operationally convenient approach
to the one-pot synthesis of some new functionalized azo
compounds, based on the aromatic electrophilic substitu-
tion reaction between the conjugate base of phenol moiety
of diazo compounds and a vinyltriphenyl phosphonium
salt. The characterization of the products was done by differ-
ent spectroscopic techniques. According to these data, the
intramolecular hydrogen bonding could determine the azo-
benzene reactivity and consequently, the final structure of
their derivatives. The DFT investigation is used to study the
molecular structures and the stability of products. The ob-
tained results have been shown that the theoretical calcula-
tions are in a good agreement with the experimental results.
Diazotization and Coupling
The azo compounds 1 and 4 were synthesized by the
usual azo coupling reaction of resorcinol with substituted
aryldiazonium salts as described below.
Fine powdered NaNO2 (3.74 g, 0.05 M) was added
slowly and with stirring to the mixture of 4-methyl aniline
(5.35 g, 0.05 M) or aniline (9.3 g, 0.1 M), HCl (12.5 mL)
and H2O (12.5 mL). Temperature must be held below 5 °C.
The solution was then added dropwise to a mixture of res-
orcinol (5.50 g, 0.05 M) and Na2CO3 (6.36 g, 0.06 M) in
H2O (20 mL), stirred for 1 h. The products were purified by
diluted sulfuric acid. Precursor 1 and 4 were obtained
(10.26 g and 14.31 g, 90%), mp. 108-109 °C and mp.
EXPERIMENTAL
All the reagents and solvents were of reagent-grade
* Corresponding author. Tel: +982144131316; Fax: +982144131316; E-mail: rahebeha@gmail.com
J. Chin. Chem. Soc. 2013, 60, 45-52
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45

Article
Amiri et al.
120-121 °C respectively.
similar to 3a by using bisazo pigment 4 (0.214 g, 0.001 M)
and DMAD (0.14 g, 0.001 M). The product was obtained as
dark red powder, yield: (80%), mp. 136 °C. UV-VIS
(CHCl3): lmax = 437 nm (log e = 3.75). IR (KBr) vmax/cm-1:
Preparation of 5-hydroxy-2-oxo-6-para-tolylazo-2H-
chromene-4-carboxylic acid methyl ester (3a)
A mixture of DMAD (dimethyl acetylene dicarbox-
ylate) (0.284 g, 0.002 M) in chloroform (3 mL) was added
drop wise to a magnetically stirred solution of triphenyl-
phosphine (0.53 g, 0.002 M) and 4-para-tolylazo-ben-
zene-1,3-diol 1 (0.428 g, 0.002 M) in chloroform (17 mL)
at -5 °C for 10 min. The reaction mixture was then allowed
to warm up to room temperature and refluxed for 16 h. The
solvent was removed under reduced pressure and the resi-
due was purified by column chromatography using n-hex-
ane-EtOAc-CH2Cl2 (3:0.5:1.25). The product was ob-
tained as black red powder, yield: (71%), mp. 118 °C. UV-
1
3447 (O-H), 1733 and 1651 (2 C=O); H NMR (CDCl3)
d/ppm: 3.74 and 3.87 (s, 6 H, 2 OCH3), 7.10 (s, 1 H, CH in
vinyl moiety), 7.23-7.38 (br. 2 H, ArH in diazobenzene),
7.40 (s, 1 H, ArH in resorcinol moiety), 7.42-7.53 (m, 6 H,
ArH in diazobenzene), 7.63-7.68 (br. 2 H, ArH in diazo-
benzene), 15.72 (s, 1 H, OH), 16.4 (s, 1 H, OH); 13C NMR
(CDCl3) d/ppm: 59.92 (2 OCH3), 110.04 (CH), 112.62 (C),
121.66-130.73 (4 CH), 137.42-142.32 (3 C), 157.18 (2
C-OH), 177.09 (2 C=O). Anal. Calcd. For C24H20N4O6 (Mr
= 459.0). MS (EI, 70 eV): m/z = 460 (M+ +1).
VIS (CHCl3): lmax = 368 nm (log e = 2.40). IR (KBr) vmax
/
Preparation of 2-(2,6-dihydroxy-3,5-bis-phenylazo-
phenyl)-but-2-en dioic acid diethyl ester (5b)
cm-1: 3448 (O-H), 1736 and 1650 (C=O); 1H NMR (CDCl3)
d/ppm: 2.45 (s, 3 H, ArCH3), 4.01 (s, 3 H, OCH3), 6.30 (s, 1
H, CH in lactone moiety), 6.97 (d, 3JHH = 9 Hz, 1 H, ArH in
chromene), 7.95 (d, 1 H, ArH in chromene), 7.35 (br. 2 H,
ArH in tolylazo), 7.75 (br. 2 H, ArH in tolylazo), 15.90 (s, 1
H, OH); 13C NMR (CDCl3) d/ ppm: 21.95 (CH3), 53.49
(OCH3), 116.94 (CH), 118.43 (C), 126.54-130.91 (6 CH),
141.45-143.34 (4 C), 165.61 (C-OH), 166.70 (C-O), 178.46,
180.81 (2 C=O). Anal. Calcd. For C18H14N2O5 (Mr =
337.1). MS (EI, 70 eV): m/z = 338 (M+ +1).
Compound 5b was prepared and purified in a manner
similar to 5 by using diethylacetylendicarboxylate (0.17 g,
0.001 M) instead of DMAD. The product was obtained as
dark red powder, yield: (73%), mp. 140 °C. UV-VIS (CHCl3):
lmax = 435 nm (log e = 3.70). IR (KBr) nmax/cm-1: 3428
(O-H), 1722 and 1646 (2 C=O); 1H NMR (CDCl3) d/ppm:
4.18 and 4.32 (q, 4 H, 3JHH = 9.2 Hz, 2 OCH2), 1.24 (t, 3 H,
3JHH = 9.2 Hz, CH3), 1.34 (t, 3 H, 3JHH = 9.2 Hz, CH3), 7.09
(s, 1 H, CH in vinyl moiety), 7.29-7.32 (br. 2 H, ArH in
diazobenzene), 7.41 (s, 1 H, ArH in resorcinol moiety),
7.43-7.50 (m, 6 H, ArH in diazobenzene), 7.63-7.66 (br. 2
H, ArH in diazobenzene), 15.72 (s, 1 H, OH), 16.40 (s, 1 H,
OH); 13C NMR (CDCl3) d/ppm: 14.41 (2 CH3), 63.02 (2
OCH2), 107.80 (CH), 110.20 (C), 121.70-137.34 (4 CH),
140.01-150.60 (3 C), 156.95 (2 C-OH), 159.70 (2 C=O).
Anal. Calcd. For C26H24N4O6 (Mr = 487.0). MS (EI, 70 eV):
m/z = 488 (M+ +1).
Preparation of 5-hydroxy-2-oxo-6-para-tolylazo-2H-
chromene-4-carboxylic acid ethyl ester (3b)
Compound 3b was prepared and purified in a manner
similar to 3a by using diethyl acetylene dicarboxylate (0.34
g, 0.002 M) instead of DMAD. The product was obtained
as red powder, yield: (75%), mp. 123 °C. UV-VIS (CHCl3):
lmax = 368 nm (log e = 2.40). IR (KBr) vmax/cm-1: 3443
(O-H), 1736 and 1661 (2 C=O); 1H NMR (CDCl3) d/ppm:
1.45 (t, 3 H, 3JHH = 7.2 Hz, CH3 in ethoxy), 2.46 (s, 3 H,
ArCH3), 4.53 (q, 2 H, 3JHH = 7.2 Hz, OCH2), 6.30 (s, 1 H,
CH in lactone moiety), 6.98 (d, 1 H, 3JHH = 9 Hz, ArH in
chromene), 7.97 (d, 1 H, 3JHH = 9 Hz, ArH in chromene),
7.34 (br. 2 H, ArH in tolylazo), 7.73 (br. 2 H, ArH in tol-
ylazo), 15.84 (s, 1 H, OH); 13C NMR (CDCl3) d/ppm: 14.52
(CH3), 21.95 (CH3), 61.48 (OCH2), 116.90 (CH), 118.40
(C), 126.48-130.92 (6 CH), 141.48-143.32 (4 C), 165.29
(C-OH), 166.22 (C-O), 178.47, 180.88 (2 C=O). Anal.
Calcd. For C19H16N2O5 (Mr = 351.2). MS (EI, 70 eV): m/z =
352 (M+ +1).
RESULTS AND DISCUSSION
The reaction of dialkyl acetylenedicarboxylate with
monoazo or bisazo compouds 1 and 4 in the presence of
triphenylphosphine was carried out in chloroform at reflux
temperature. The products of the first reaction as shown in
Scheme I are azo-coumarin derivatives 3a and 3b.
It was found that bisazo compound 4 reacts with
Dimethyl or Diethyl acetylenedicarboxylate catalyzed by
PPh3 to produce 2-(2,6-dihydroxy-3,5-bis-phenylazo-
phenyl)-but-2-en dioic acid di-methyl ester 5a and 2-(2,6-
dihydroxy-3,5-bis-phenylazo-phenyl)-but-2-en dioic acid
di-Ethyl ester 5b (Scheme II). Apparently, the bisazo re-
Preparation of 2-(2,6-dihydroxy-3,5-bis-phenylazo-
phenyl)-but-2-ene dioic acid dimethyl ester (5a)
Compound 5a was prepared and purified in a manner
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JOURNAL OF THE CHINESE
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Influence of H-bonding on the Synthesized Azo Derivatives Structures
Synthesis of azo-coumarin derivatives 3a
and 3b
Spectral characterization
Scheme I
The structures of compounds 3a-b and 5a-b deduced
from their IR, 1H and 13C NMR spectrums. The mass spec-
tra of these compounds displayed molecular ion peaks at
appropriate m/z values. The 1H NMR spectrum of 3a exhib-
ited four singlet readily recognized as arising from hydrox-
yl (d = 15.95 ppm) proton, methyne of lacton group (d =
6.30 ppm), methoxy (d = 4.01 ppm), and methyl (d = 2.46
ppm) protons. Also, in this compound, the protons in phe-
nol moiety are resonated at 6.97 and 7.95 ppm as doublets
(3J = 9 Hz). The ortho coupling constant shows the arrange-
ment of lacton unit in this structure.
Scheme II Synthesis of bisazo compound 5a and 5b
The 13C NMR spectrum of 3a shows eighteen distinct
resonances in agreement with the proposed structure. The
1H and 13C NMR spectrums of 3b (Figure 1) is similar to
that of 3a except for the ethoxy group instead of methoxy
which give rise to characteristic signal in appropriate re-
gion of the spectrum (d = 4.53 ppm as quartet for OCH2 and
d = 1.45 ppm as triplet for CH3).
The 1H NMR spectrum of 5a displayed a characteris-
tic five singlet sharp lines identified as two hydroxyl
groups (d = 15.72 and 16.4 ppm) protons, methyne (d =
7.10 ppm), two methoxy groups (d = 3.74 and 3.87 ppm).
The 13C NMR spectrum of 5a showed resonances in agree-
ment with the proposed structure but the number of signals
of it is reduced because of the molecular symmetry (Figure
2). Partial assignments of these resonances are given in the
experimental section. The 1H and 13C NMR spectrum of 5b
are similar to those of 5a except for the ester groups.
As can be seen in 1H NMR spectrum of products 3a-b
and 5a-b, the phenolic protons have displayed the up-field
chemical shifts (15.72-16.4 ppm) arising from intramolec-
agent 4 afforded mostly the uncyclized products. The main
reason for this phenomenon could be hydrogen bonding
between two –OH groups of resorcinol and the adjacent
diazo units.
A plausible mechanism for the formation of azo-
coumarin derivatives 3a and 3b is shown in Scheme III.12
The reaction starts with nucleophilic attack of triphenyl-
phosphine on the p-deficient acetylenic compound and
subsequent protonation of the reactive 1:1 adduct by phe-
nol moiety in diazo compound. Then, the positively charged
ion A is attacked by the conjugate base of the phenol. The
product is presumably produced by intramolecular lacto-
nization of the unsaturated diester intermediate (Scheme
III).
The mechanism of the formation of azo-
Scheme III
coumarin derivatives 3a-b
Fig. 1. The 1H and 13C NMR spectrums of 3b.
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Article
Amiri et al.
ular hydrogen bonding with diazo groups.
of DFT methods, implementing the 6-31g basis set has
been employed to optimize the molecules.
UV spectra
The diazo compound 1 has its maximum absorption at
383 nm (log e = 1.80) corresponding to the p-p* transition
of trans-azobenzene while structure 3a exhibit a maximum
absorption at 368 nm (log e = 2.40). We can explain these
phenomenons as follow:
The nature of optimized geometries at the B3LYP
level has been checked with frequency calculations. Vibra-
tional frequencies were calculated at the 6-31g basis set for
all minima and transition state, which were confirmed to
have zero and one imaginary frequency, respectively.
Geometry and stability of structures
When the new chemical bond (-O-C=O) of chromene
moiety is produced in structure 3a, the structural change of
the -OH donor group in azo compound 1, will decrease the
electron-release behavior and cause the blue shift of 15 nm
as a result. But the value of the logarithm of molar extinc-
tion coefficient of pigment 3a is bigger than the primary
azo compound 1 and it seems to be reasonable because of
the increasing in the length of the conjugated system.
Whereas, the absorption maxima of the bisazo compound 4
is 427 nm (log e = 2.60) which in comparison with product
5a (lmax = 437 nm and log e = 3.75) shows the red shift of
10 nm. It was obvious that when the additional chromo-
phores (-N=N- and -C=C-) was produced in compound 5a,
the absorption maximum of it revealed a bathochromic
shift with the higher intensity.
The domino reactions of monoazo 1 and bisazo 4 with
reagent 2 can take place along two reaction routes that pro-
duced coumarin derivative or open chain species (path 1
and path 2 of Scheme IV respectively). The experimental
results indicated that monoazo 1 produced coumarin deriv-
ative, while bisazo 4 produced open-chain species in the
mentioned reactions (Schemes I and II).
The different possibilities of the reaction
between monoazo and bisazo 1, 4 with
DMAD (2a)
Scheme IV
THEORITICAL CALCULATIONS
All calculations were performed using the Gaussian
03 program.13 Geometries for all structures were fully opti-
mized by means of analytical energy gradients by Berny
optimizer with no geometrical constraint. Becke’s three-
parameter (B3) adds part of the Hartree-Fock exchange en-
ergy into its exchange part14 combined with the gradient-
corrected correlation functional of Lee–Yang–Parr (LYP)15
To further investigate these results, we decided to
have closer study by theoretical method. DFT calculations
at B3LYP level was used to full optimized structure of com-
pounds and the calculations of the reaction Gibbs free ener-
gies (DGr) for all of the paths. The results obtained for the
reaction of monoazo 1 with reagent 2a showed that DGr of
path 1 is 95.5 kJmol-1 lower than path 2, therefore coumarin
derivative (3a) is produced. While in the reaction of bisazo
4 with the same reagent, path 2 is predominated by 78.8
kJmol-1.
Moreover, DFT studies were used to investigate of
possibilities in the formation of coumarin derivative by at-
taching of –O1H or –O2H to –CO2R in cyclization reaction
of intermediate 6 (Scheme V). The results of experiment in-
dicated that the dominant product was 3a. To further inves-
tigate this result we decided to have closer study by theoret-
ical method.
Fig. 2. The 1H and 13C NMR spectrums of 5a.
In the first step, the structure of compounds 3a, 6 and
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JOURNAL OF THE CHINESE
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Influence of H-bonding on the Synthesized Azo Derivatives Structures
electrophilicity index, wk, by this equation: wk = wƒ + on
The regioselectivity route for intramolecu-
lar reaction of intermediate of 6
Scheme V
k
which ƒ +k is the Fukui function for a nucleophilic attack.20
This expression shows that whenever ƒ +k has its maximum
value, the active site is an electrophile. It is expected that in
compound 6, the most favorable pathway corresponds to
the bond formation between at the most electrophilic and
nucleophilic sites.
The calculated local properties of compound 6 are
summarized in Table 2. The C10 site presents a larger local
electrophilicity value than C8 site; therefore C10 will be pre-
ferred a position for the nucleophilic attack. Though, there
is not any significant differences between ƒ - of O1 (0.0298)
k
and O2 (0.0268), therefore the higher steric hindrance in
ortho position is predominant forces in formation of prod-
uct 3a.
8 were fully optimized at B3LYP/6-31G level of theory,
which the results of calculations were shown in Table 1. As
can be seen from this table, compound 3a is more stable
than compound 8 by 112.1 kJmol-1. The dihedral angle of
NNCC (j3) in compound 3a was 0.820, which leads to an
increased planarity of azobenzen skeleton, in consequence,
may enhance the optical activity,16-19 while this dihedral an-
gle (j3) in compound 8 was 57.50. Moreover, the hydrogen
bonding between phenolic hydroxyl (-O1H) and diazo units
prevents it to participate in cyclization reaction.
Intramolecular hydrogen bonding
To investigate the energetic of intramolecular H-
bonds based on conformational analysis; the enthalpy of an
H-bond is assessed by comparing the energies of three con-
Table 2. Fukui function and local electrophilicity at the active
sites of compound 6
fk+
fk-
Atom number
wk (ev)
In the next step, DFT-based reactivity descriptors in-
cluding Fukui function and local electrophilicity indices
were used to investigate for the active sites in compound 6.
The Fukui function is one of the more common de-
scriptors of site reactivity, which can be related to local
C8
0.0013
-
0.0030
C10
O1
O2
0.0044
-
0.0096
-
-
0.0298
0.0268
-
-
Table 1. Calculated total and zero-point vibrational energies (Hartree; zero-point vibrational
energy is scaled by a factor of 0.9613 to eliminate known systematic errors in
calculations), relative energy (including zero-point energy, kJmol–1) and selected
structural parameters of compounds 3a and 6-7
3a
6
8
B3LYP/6-31G
ZPE
-1179.5959813
-1295.2730892
0.354352
-
-1179.55194535
0.299639
0.301059
0.0
Erel / kJmol-1
112.1
O1H
O2H
O1C2 r3/Å
N1N2 r4/Å
r1/Å
r2/Å
1.039
-
1.351
1.293
1.033
0.999
1.357
1.295
0.988
1.388
1.265
HO1C2
O1C2C3 q2/°
HO2C4
O2C4C3 q4/°
C1N1N2 q5/°
HO1C2C3 j1/°
HO2C4C3 j2/°
N2N1C1C2 j3/°
q1/°
107.06
119.84
-
120.76
116.66
179.51
-
107.19
118.47
110.61
112.96
116.93
178.60
46.38
-
114.88
112.58
124.95
125.24
-
q3/°
23.57
57.50
0.820
0.207
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Article
Amiri et al.
Table 3. Calculated total and zero-point vibrational energies (Hartree; zero-point vibrational
energy is scaled by a factor of 0.9613 to eliminate known systematic errors in
calculations), relative energy (including zero-point energy, kJmol–1) of conformers
3a, IH1 and IH2
3a
IH1
IH2
B3LYP/6-31G
ZPE
-1179.5959813
0.301059
0.0
-1179.5703400
0.301042
67.29
-1179.5755703
0.301044
53.58
Erel / kJmol-1
HO1C2C3
j1/°
179.51
30.21
9.46
erism has been very useful in rationalizing some aspects of
the chemical bond, because of the proton is able to form a
chemical bond with two different atoms of the same mole-
cule, so in the most cases, the stability of both isomers are
different.24
formers that differ by an intramolecular stabilizing interac-
tion, which can be associated with a hydrogen bond. Three
isomeric forms of the compound 3a were investigated by
theoretical study. The ground-state of 3a is stabilized by the
intramolecular H-bond as shown in Scheme VI, whereas
other isomers are stabilized by intramolecular H-bonds of
IH1 and IH2. The energy differences between them be as-
sociated with the strong of the intramolecular H-bond for-
mation. The results of these calculations which are summa-
rized in Table 3, confirmed that the 3a isomer is more stable
than the others which due to H-bonding between phenolic
hydroxyl and diazo group.
Resorcinol moiety in the product 5a can easily
changes to its tautomeric form and it can help to cis-trans
isomerisation which is important for photo switching prop-
erty.18 So, in continuation of our studies, we investigated
the existence possibility of tautomeric structures in com-
pound 5a from energetic points of view. DFT method was
used to describe the molecular geometries of compound 5a
and its tautomer (9) with the corresponding transition state
and the activation energy of tautomerization (Scheme VII).
The results of calculations in Table 4 showed that com-
pound 9 is less stable than compound 5a by 15.18 kJmol-1.
This energy difference could be attributed to the inter-
amolecular hydrogen bonding in compound 5a. Notably,
the transition state of the intramolecular proton transfer in
tautomerization process is significantly stabilized by the
formation of a stable six – membered ring. As can be seen
in Table 4, the bond orders between the oxygen (O1) and C2
atom (1.304), and between the nitrogen (N1) and C1 atom
(1.374) in the transition state correspond to partially double
bonds. The energy barrier for the tautomerization process
is 39.24 kJmol-1.
Scheme VI Three isomeric forms of compound 3a
Scheme VII Compound 5a and its tautomer (9)
Theoretical calculations of azo-enol hydrazo tautom-
erism
When two isomers differ by the placement of an atom
or a functional group and an interconversion equilibrium is
established, this process is referred as a tautomeric equilib-
rium and the isomers are known as tautomers.21,22 Tautom-
erism arising from an intramolecular proton transfer occurs
frequently in many chemical systems, such as keto-enol
and imine-enamine equilibrium, amino acid zwiterionic
forms and metabolic intermediates.23 The study of tautom-
CONCLUSION
The one-pot nature of the present procedure without
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Influence of H-bonding on the Synthesized Azo Derivatives Structures
Table 4. Calculated total, zero-point vibrational energies, relative energies and selected
geometrical parameters of compounds 5a, 9 and transition state (Ts)
5a
Ts
9
B3LYP/6-31G
ZPE
E
-1589.6840069
0.420388
0.0
-1589.6651413
0.416304
39.24
-1589.6791875
0.421387
15.18
rel / kJmol-1
N1N2
O1H
O1C2
N2H
C1C2
N1C1
HN2N1
HO1C2
HO1C2C1
HN2N1C1
C2C1N1N2
r1/Å
r2/Å
r3/Å
r4/Å
r5/Å
r6/Å
q1/°
q2/°
j1/°
j2/°
j3/°
1.292
1.035
1.349
1.586
1.436
1.397
104.99
113.08
1.69
1.254
1.235
1.304
1.220
1.424
1.374
109.73
105.54
0.625
0.0215
0.186
1.282
1.832
1.253
1.007
1.459
1.320
117.98
104.31
1.19
0.033
0.071
0.015
0.075
Atvars, T. D. Z.; Oliveira, Jr., O. N.; Mendonca, C. R. Opt.
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any modification makes it an acceptable method for the
preparation of substituted azo compounds 3a-b and 5a-b
with variable functionalities. The products structural inves-
tigations have been shown the hydrogen bonding forma-
tion in primary azobenzene 4 will prevent the next lacto-
nization in products 5a-b because of the hydroxyl groups’
position. Theoretical calculations are expected in principle
to produce some properties and structural features can be
obtained with an accuracy that is competitive with experi-
ment. According to the results obtained, the hydrogen
bonding in azobezene derivatives should be an effective
factor on their stability. Intramolecular H-bonding could
constitute a six-membered ring intermediate which en-
hances planarity and subsequently increases the resonance
possibility.
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