Electronic, infrared, and 1HNMR spectral studies of the novel charge-transfer complexes of o-tolidine and p-toluidine with alternation π-acceptors (3,5-dinitro benzoic acid and 2,6-dichloroquinone-4-chloroimide) in CHCl3 solvent

Article abstract of DOI:10.1016/j.saa.2005.07.076

The rapid interaction between o-tolidine and p-toluidine (π-donors) with the π-acceptors, e.g., 3,5-dinitrobenzoic acid (DNB) and 2,6-dichloroquinone-4-chloroimide (DCQ) results in the formation of 1:1 charge-transfer complexes as the final products, [(o-

Full text of DOI:10.1016/j.saa.2005.07.076

Spectrochimica Acta Part A 64 (2006) 778–788
Electronic, infrared, and 1HNMR spectral studies of the novel
charge-transfer complexes of o-tolidine and p-toluidine with
alternation ␲-acceptors (3,5-dinitro benzoic acid and
2,6-dichloroquinone-4-chloroimide) in CHCl3 solvent
Moamen S. Refata,∗, Sadeek A. Sadeekb, Hana M. Khaterb
a
Department of Chemistry, Faculty of Education, Port-Said, Suez-Canal University, Port Said, Egypt
b
Department of Chemistry, Faculty of Science, Zagazig University, Zagazig, Egypt
Received 18 April 2005; accepted 15 July 2005
Abstract
The rapid interaction between o-tolidine and p-toluidine (␲-donors) with the ␲-acceptors, e.g., 3,5-dinitrobenzoic acid (DNB) and 2,6-
dichloroquinone-4-chloroimide (DCQ) results in the formation of 1:1 charge-transfer complexes as the final products, [(o-tolidine) (acceptor)]
1
and [(p-toluidine) (acceptor)]. The final products of the reactions have been isolated and characterized using FTIR, HNMR spectroscopy
and elemental analysis as well as photometric titration. The stoichiometry and apparent formation constants of the complexes formed were
determined by applying the conventional spectrophotometric molar ratio method.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Charge-transfer; o-Tolidine; p-Toluidine; 2,6-Dichloroquinone-4-chloroimide; 1HNMR spectra
1. Introduction
formed during the reaction of electron donors (nickel(II) and
Fe(III) acetylacetonates, polyamido-amine dendrimers 1,8-
naphthalimide polyamidoamine (PAM1) and 4-piperidino-
1,8-naphthalimide polyamidoamine (PAM2), benzanthrone
derivatives) with iodine and different ␲-acceptors like DDQ,
TCNQ, and p-chloranil.
The present investigation tends to elucidate mainly the
study of the reactions of both 3,5-dinitrobenzoic acid
(DNB) and 2,6-dichloro quinone-4-chloroimide (DCQ) (␲-
acceptors) for the first time with o-tolidine and p-toluidine
(electron donors) and interpreting the nature of these inter-
actions using 1HNMR, IR-spectral, electronic absorption as
well as elemental analysis data.
Many of the electron donor–acceptor (EDA) interac-
tions had been widely studied spectrophotometrically in
the determination of drugs that are easy to be deter-
mined based on CT-complex formation with some electron
acceptors. 2,6-Dichloroquinone-4-chloroimide (DCQ, Gibbs
reagent), 7,7ꢀ,8,8ꢀ-tetracyanoquinodimethane (TCNQ), p-
chloranil (CL) and chloranilic acid (CLA) are strong ␲-
acceptors drugs and the review of literature in the last
decade have been mainly concentrated on the CT-complexes
spectral studies [1–5]. A vast number of the charge-
transfer complexes formed during the reaction of ␴- and
␲-acceptors with organic compounds containing different
sites of donation (nitrogen, oxygen, or sulfur atoms) were
extensively investigated [6–10]. This paper is a contin-
uation of our previous investigation [11–14] concerned
with the formation of stable charge-transfer complexes
2. Experimental
Reagent grade chemicals were used throughout. p-Tolu-
idine and 2,6-dichloroquinone-4-chloroimide were obtained
from Merck Chemical Co., while o-tolidine and 3,5-dini-
trobenzoic acid were obtained from Aldrich Chemical Co.
∗
Corresponding author.
E-mail address: msrefat@yahoo.com (M.S. Refat).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.07.076

M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
779
2.1. Analysis and physical measurements
of the elemental analyses (%, yield), (mp, ◦C), and color are
given in Table 1.
Electronic spectra were recorded at room temperature
via both Shimadzu UV-Spectrophotometer model 1601 PC
with quartz cell of 1 cm path length and Jenway 6405 Spec-
trophotometer each for certain reactions. IR-spectra, as KBr
discs, were recorded on a Gensis II FT-IR spectrophotometer
2.4. [(o-Tolidine) (DCQ)] (1) and [(p-toluidine) (DCQ)]
(3)
A
brown solution of the 2,6-dichloroquinone-4-
1
(400–4000 cm−1). HNMR spectra in dmso-d6 were mea-
chloroimide (DCQ, acceptor) (0.841 g, 4 mmol) in C2H5OH
(25 ml) was added at room temperature to each of the two
colorless solutions (two donors) of o-tolidine (0.212 g,
1 mmol) and p-toluidine (0.107 g, 1 mmol) in C2H5OH
(15 ml) and then stirred for about 15 min. The dark brown
(complex 1) and dark green (complex 3) precipitates formed
were filtered off, washed with the diethyl ether (3 ml) and
dried in vacuum over CaCl2.
sured on a Varian Gemini 200 MHz Spectrometer using TMS
as an internal standard. Microanalysis for carbon, hydrogen,
nitrogen, and chloride were carried out at the Micro analytical
centers, Cairo University, Cairo, Egypt using a Perkin-Elmer
CHN 2400.
2.2. Photometric measurements
The photometric titration measurements were carried out
within the reactions between the acceptors (DCQ and DNB)
and the two donors (o-tolidine and p-toluidine) in CHCl3 at
20 ◦C. The concentration of the two donors in the reactions
mixtures were kept fixed (1.0 × 10−4 M) while the concen-
tration of the acceptors DCQ and DNB changed over a wide
range of concentrations (0.25 × 10−4 to 3.0 × 10−4 M) to
produce solution in each case of acceptor: donor molar ratio
varying from 1.0:0.25 to 1.0:3.0. The peak absorbance of the
resulted CT-complexes at 301 nm for [(o-tolidine) (DCQ)],
249 and 291 nm for [(o-tolidine) (DNB)], 245 and 270 nm for
[(p-toluidine) (DCQ)], and 290 nm for [(p-toluidine) (DNB)]
were measured for each reaction mixture and plotted as a
function of the two acceptors (DCQ or DNB) to two donors
(o-tolidine or p-toluidine) molar ratio. The stoichiometry of
the molecular CT-complexes under investigation were deter-
mined by the application of the conventional spectrophoto-
metric molar ratio according to the known methods [15] and
were also used to obtain the modified Benesi–Hildebrand
plots [16–18] in order to calculate the formation constant,
K, and the absorpativity, ε, values for each CT-complexes
resulted from this study.
2.5. [(o-Tolidine) (DNB)] (2) and [(p-toluidine) (DNB)]
(4)
To the two solutions of o-tolidine (0.212 g, 1 mmol) and
p-toluidine (0.107 g, 1 mmol) in CHCl3 (15 ml), a satu-
rated solution of 3,5-dinitrobenzoic acid (0.636 g, 3 mmol)
in CHCl3 (50 ml) was added (to each mentioned donor). The
two novel orange colored CT-complexes for each donor (o-
tolidine or p-toluidine) resulted were filtered off, washed with
CHCl3 (5 ml) and dried in vacuum over CaCl2.
3. Results and discussion
The electronic absorption spectra (UV–vis) of the donors,
o-tolidine and p-toluidine (1.0 × 10−4 M) with different elec-
tron ␲-acceptors (2,6-dichloroquinone-4-chloroimide and
3,5-dinitro benzoic acid (1.0 × 10−4 M) under investigation
in chloroform solution show an extra absorption band not due
to any one of the components alone (Fig. 1). Furthermore,
neither electron donors nor electron acceptors is absorbed
in the region of absorption of the molecular complexes
formed. These bands have been attributed to the formation
of donor–acceptor molecular complexes in these solutions.
The CT-absorption bands represented in the spectra due to
the resulted CT-complexes were appeared at 301 nm (very
strong band, hyperchromic effect) for [(o-tolidine) (DCQ)]
(1), at 249 and 291 nm for [(o-tolidine) (DNB)] (2), at 245 and
270 nm for [(p-toluidine) (DCQ)] (3) (hyperchromic effect
2.3. Preparation and characterization of the
CT-complexes
IR, 1HNMR, and electronic UV–vis spectroscopy, as well
as micro analytical analyses elucidated structures of the for-
mation of CT-complexes reported in this study. The results
Table 1
Analytical and physical data of [(o-tolidine) (DCQ)] (1), [(o-tolidine) (DNB)] (2), [(p-toluidine) (DCQ)] (3), and [(p-toluidine) (DNB)] (4) CT-complexes
Compound, MF (MW
)
Elemental analyses, %found (calculated)
Color
Yield (%)
mp (◦C)
C
H
N
Cl
C
C21
20H18N3OCl3 (1) (422.74)
56.24 (56.77)
59.17 (59.37)
48.98 (49.11)
52.44 (52.61)
4.19 (4.25)
4.63 (4.71)
3.40 (3.46)
3.97 (4.07)
9.72 (9.93)
13.08 (13.19)
8.75 (8.81)
24.97 (25.19)
–
33.27 (33.53)
–
Dark brown
Orange
Dark green
Orange
67
89
91
77
167
138
173
134
H
20N4O6 (2) (424.41)
C13H11N2OCl3 (3) (317.61)
14H13N3O6 (4) (319.28)
C
13.05 (13.15)

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M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
Fig. 1. Electronic absorption spectra of (A) [(o-Tolidine) (DCQ)] reaction in CHCl3; (B) [(o-tolidine) (DNB)] reaction in CHCl3; (C) [(p-toluidine) (DCQ)]
reaction in CHCl3; (D) [(p-toluidine) (DNB)] reaction in CHCl3. d, donor (1 × 10−4 M); a, acceptor (1 × 10−4 M); c, donor–acceptor CT-complex.
for two bands and noted that the main peak at 245 nm for
p-toluidine have been reduced (hypochromic effect)) and
at 290 nm for [(p-toluidine) (DNB)] (4). The stoichiometry
of the [(o-tolidine) (acceptor)] and [(p-toluidine) (accep-
tor)] (where acceptor = 2,6-dichloro quinone-4-chloroimide
or 3,5-dinitrobezoic acid) reactions were shown in all cases to
be of ratio 1:1. This was concluded according to the obtained
elemental analysis data of the isolated solid CT-complexes
as indicated in the experimental section, as well as from the
complexes infrared spectra, which indicate the existence of
the bands which characterize both the donors and the two
acceptors. The stoichiometry of 1:1 is also strongly supported
by photometric titration measurements. These measurements
were based on detected bands at 301 nm for [(o-tolidine)
(DCQ)] (1); at 249 and 291 nm for [(o-tolidine) (DCQ)]
(2); at 245 and 270 nm for [(p-toluidine) (DCQ)] (3); at
290 nm for [(p-toluidine) (DNB)] (4). In these measure-
ments, concentration of o-tolidine and p-toluidine was kept
fixed, while the concentration of the acceptors (at the same)
were varied over the range of 0.25 × 10−4 to 3.00 × 10−4 M
as illustrated in Section 2. Photometric titration curves based
on these measurements are shown in Fig. 2. The base-
acceptors equivalence points indicate that the ratio in all
cases is 1:1 and this result agrees quite well with the ele-
CT-complexes. Accordingly, the formed CT-complexes upon
the reaction of o-tolidine or p-toluidine as donors with the
␲-acceptors under investigation in CHCl3 have the gen-
eral formula [(o-tolidine) (DCQ)], [(o-tolidine) (DNB)], [(p-
toluidine) (DCQ)] and [(p-toluidine) (DNB)]. The 1:1 mod-
ified Benesi–Hildebrand Eq. (1) [16–18] was used in the
calculations the values of the equilibrium constant, K, and
the absorpativity, ε.
Ca0Cd0L
A
1
Kε
Ca0Cd0
ε
=
+
(1)
Ca0 and Cd0 are initial concentration of the ␲-acceptors (DCQ
andDNB)andthedonors(o-tolidineand p-toluidine), respec-
tively, whereas L refers to optical path length of the cell,
while A is the absorbance of the illustrated bands for the
four new CT-complexes described in this study. The data
obtained throughout these calculation are translated by plot-
ting the values of Ca0 × Cd0/A against Ca0 + Cd0 values for
each donor with each acceptor, straight lines are obtained
with a slope of 1/ε and intercept of 1/Kε as shown in Fig. 3,
for the reactions of two donors in exchange with DCQ and
DNB in CHCl3. The values of the K, ε, and transition energy,
ECT associatedwiththesecomplexes[(o-tolidine) (acceptor)]
and [(p-toluidine) (acceptor)] are given in Table 2. These high
1
mental analysis, HNMR, and infrared spectra of the solid

M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
781
Fig. 2. Photometric titration curves for the donor–acceptor reactions in CHCl3. (A) [(o-Tolidine) (DCQ)] reaction at 301 nm; (B) [(o-tolidine) (DNB)] reaction
at 249 and 291 nm; (C) [(p-toluidine) (DCQ)] reaction at 245 and 270 nm; (D) [(p-toluidine) (DNB)] reaction at 290 nm.
values of K confirm the expected high stabilities of the formed
CT-complexes as a result from the expected high donation of
the donors (o-tolidine and p-toluidine). The K values obtained
are listed in Table 2. When examining the results given in
Table 2, it is evident that the order of increasing the sta-
bility of the 1:1 intermolecular charge-transfer complexes
formed varies depending on the nature of the electron donor
and acceptor compounds including the type of electron with-
drawing substitutes suchashalo and nitrogroupsaccordingto
the following sequence: [(o-tolidine) (DCQ)] > [(o-tolidine)
(DNB)] > [(p-toluidine) (DCQ)] > [(p-toluidine) (DNB)].
Consequently, the high values of the stability (K) for
these CT-complexes resulted above can be interpreted as fol-
lows: the ground state of the charge-transfer complexes under
investigation has no-bond structure, while the excited state
has predominantly a dative structure i.e. the structure D+–A−.
This supports the idea that this dative structure is ionic inter-
mediate [D+A−]. Such spectral features (Fig. 1) are in agree-
ment with those reported before for the DDQ− (DDQ = 2,3-
dichloro-5,6-dicyano-1,4-benzoquinone) radical ion [19].
The mid infrared spectra of the o-tolidine, p-toluidine,
DCQ, DNB, [(o-tolidine) (DCQ)], [(o-tolidine) (DNB)], [(p-
toluidine) (DCQ)] and [(p-toluidine) (DNB)] are shown in
(Fig. 4) while their band assignments are given in Table 3.
If we looked comprehensively, for the first time at the IR-
Figures (Fig. 4) for donors, acceptors, and CT-complexes
that result from the interaction between the donors and
acceptors, we find out that the peaks have shifted to the
lower or higher wavenumbers. We could observe also that
the peaks of CT-complexes have decreased in intensity.
This supports the complexation between the donors and
acceptors.
Table 2
Maximum absorption wavelengths λmax (nm), absorpativity εmax (l mole−1 cm−1), transition energies (Kcal mole−1) and formation constants K (l mole−1) of
molecular CT-complexes formed in CHCl3
CT-complexes
λmax (nm)
εmax (l mole−1 cm−1
)
K (l mole−1
2.57 × 104
)
ECT (kcal mole−1
)
[(o-Tolidine) (DCQ)]
[(o-Tolidine) (DNB)]
[(p-Toluidine) (DCQ)]
[(p-Toluidine) (DNB)]
301
291
270
290
3.61 × 104
7.27 × 104
2.83 × 104
1.70 × 104
95.00
98.27
105.91
98.61
0.647 × 104
0.545 × 104
0.417 × 104

782
M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
Fig. 3. The plot of (Ca0 × Cd0)/A values against (Ca0 + Cd0) values for the donor–acceptor reactions in CHCl3. (A) [(o-Tolidine) (DCQ)] reaction at 301 nm; (B)
[(o-tolidine) (DNB)] reaction at 249 and 291 nm; (C) [(p-toluidine) (DCQ)] reaction at 245 and 270 nm; (D) [(p-toluidine) (DNB)] reaction at 290 nm.
If we carefully examine the donation sites through HNMR
spectra in both o-tolidine and p-toluidine ( NH2 groups and
aromatic rings) and if also carefully examine the acceptors
sites in the other side (COOH and NO2 groups in the DNB
sites and chloro group in DCQ), we will come up with some
primary results:
(iii) In Table 3, there was a shift in the intensity of the aro-
matic character peaks for both donors and acceptors,
resulted from the ␲–␲* CT-complexes which were orig-
inally formed via the benzene rings (electron rich group
of o-tolidine or p-toluidine and both DCQ and DNB
(electron acceptors)) [2].
(i) There was a decrease in intensity for the peaks that dis-
tinguish the NH2 group (the donation sites for both
o-tolidine and p-toluidine) and also there was shifting
for the peaks towards the lower wavenumbers. We can
say that the donation process has been carried out by
NH2 group in the case of DCQ and also in the case of
DNB.
(ii) It was noticed also that the interaction between o-
tolidine and p-toluidine with 3,5-dinitrobenzoic acid
does not result in COOH group character in addi-
tion to the above mentioned change (i) in the resulting
CT-complexes. This justifies the complexation between
NH2 and COOH group in 3,5-dinitrobenzoic acid
(i.e. intermolecular hydrogen bond formed lead to the
absence of the wavenumber of the peak of free car-
boxylic group of DNB at 1704 cm−1 which existed
before complexation) indicated in IR spectra.
To create harmony between the parts of the study, we
embodied the HNMR spectra of the complexes, donors
and acceptors in Fig. 5. While their peaks assignments
and the structures of donors, acceptors and proposed CT-
complexation are given in Scheme 1.
A further study on the CT-complexes of π-acceptors
(DCQ and DNB) with both o-tolidine and p-toluidine are
discussed (Scheme 1) to their molecular structure and the dif-
ferent types of interaction involved. There are some changes
in the chemical shift values of the CT-complexes rather than
1
the free donor and acceptor. The HNMR spectrum of the
CT-complex formed from the interaction between o-tolidine
as a donor with ␲-electron acceptor (DCQ) has shifted in
NH2 group site of donation from δ 4.77 ppm (S, 4H, two
NH2 group) to δ 4.10-4.60 ppm (br S, 6H, 2 × NH3 group
of o-tolidine). This shift assures that the two amino groups
are mainly involved in the formation of the CT-complex.

M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
783
The mechanism of this reaction take place as follow:
tons in position 3H and 5H to make intermolecular hydrogen
bond with the lone pair of electron on the nitrogen atoms
for the two amino groups of o-tolidine. The electron density
around protons depends on the degree of electro negativity
If we examine the acceptor (DCQ), we find out that two
withdrawing halo groups and double bond in the para and
ortho position, respectively, are relative to the 3H and 5H.
These withdrawing groups give facility to liberate the pro-
Fig. 4. Infrared spectra of (A) o-tolidine; (B) p-toluidine; (C) DCQ; (D) DNB; (E) [(o-tolidine) (DCQ)]; (F) [(o-tolidine) (DNB)]; (G) [(p-toluidine) (DCQ)];
(H) [(p-toluidine) (DNB)] compounds.

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M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
Table 3
Infrared frequenciesa (cm−1) and tentative assignmentsb for (1) o-tolidine, (2) p-toluidine, (3) DCQ, (4) DNB, (5) [(o-tolidine) (DCQ)], (6) [(o-tolidine) (DNB)],
(7) [(p-toluidine) (DCQ)] and (8) [(p-toluidine) (DNB)]
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Assignments
3475 s
3412 s
3375 s
3338 ms
3417 ms
3375 w
3333 ms
3422 s
3460 m, br
3448 w, sh
3380 ms
3344 vw
3323 vw
3543 w,sh
3475 vw
3417 vw
3375 vw
3339 vw
3427 w,br
3433 w
3417 w
3375 w
3359 w
3338 w
ν OH of COOH; DNB ν(NH); NH2
ν(O H); water of hydration
3213 ms
3019 s
3223 w
3155 s,br
3086 sh
3061sh
3097 mw
2966 vw
2883 vw
2825 vw
3213 sh
3160 vw
3124m,br
3019 w
3113w
3014 vw
3239 mw
3024 vw
3218 w
3108 mw
ν(CH);C C H and combination
aromatic
3145 w,sh
3055 vw
3019 ms
2982 ms
2940 mw
2898 w
2919 ms
2856 w
2741 vw
–
–
2972 w
2930 w
2862 vw
2804 vw
2977 vw
2935 vw
2877 vw
2783 sh
2966 vw
2930 vw
2872 vw
2998 sh
2925 w
2867 w
2746 vw
νas CH; CH3 + νs CH3
2856 w
1870 ms
1877 ms
1777 vw
2000 s,br
1735 sh
1700 sh
1670 vs
1640 vs
1971 w
1856 w
1705 vs
2000 ms,sh
1882 w
1814w
1882 w,br
1720 vw
1646 w,sh
2191ms
1908 vw
1882 w
Overtone of: δCH;(out-of-plane) and
combination aromatic + ν(C H);
phenyl + ν(C O) + ν(C N)
1625 vs
1573 s
1520 w
1489 vs
1625 vs
1594sh
1510 vs
1604 w
1583 vs
1484 s
1447 vw
1405 vs
1631s
1620 s
1578 s
1494 vs
1447 ms
1405 ms
1619 s
1578 ms
1541 s
1494 s
1458 ms
1426 vw
1620 ms
1583 w,sh
1562 ms
1520 s
1489 s
1416 mw
1625 s
1604 s
1541 s
1510s
ν(C C); aromatic + δ (NH2) + phenyl
nucleus + νas(NO2); DNB
1600 ms
1577 vs
1479 vs
1458 s
1384 s
1321 s
1295 s
1447 sh
1405 s
1348 vw
1280 sh
–
1421 vs
1352 vs
1285 vs
1327 vw
1311 vw
1290 w
1384 ms
1348 s
1384sh
1342 s
1311 w
1285 w,sh
1259 s
1458 s
δas (CH3) + δs (CH3) νs(NO2);
DNB + ν(C O); COOH
1437 sh
1379 ms
1348 vs
1285 sh
1269 vs
1154 vs
1065 s
1039 s
1269 vs
1222 sh
1180 s
1122 s
1080 w
1049 w
1274 vs
1232 s
1217 s
1164sh
1143 vs
1070 s
1040 vs
1185 vs
1096 ms
1080 vs
1007 vw
1269 mw
1217 mw
1201 w,sh
1154 ms
1133 sh
1264 ms
1243 sh
1190 ms
1154 ms
1086 ms
1070 ms
1049 w
1217 vw
1206 vw
1185 w
1122 ms
1080 vw
1044 vw
1264 s
ν(C O); C NH2 + in-plane bending
of aromatic CH
1211 vw
1190 ms
1180 ms
1122 s
1086 w
1065 s
1065 ms
1033 w
1028 vw
986 s
944 ms
902 s
986 vw
955 vw
881 sh
813 vs
766 sh
724 vw
949 s
892 sh
860 s
810 sh
798 vs
777 s
719 w
693 w
955 ms
928 vs
866 sh
808 vs
782 ms
729 vs
991 w
876 ms
818 vs
756 s
991 vw
949 ms
929 s
944 mw
897 ms
866 sh
818 vs
777 vw
960 vw
928 s
913 s
876 mw
818 vs
719 vs
OH and CH; out-of-plane def.
(aromatic ring) + ν(C N);
C NO2 + ν(C Cl); (DCQ)
887 s
913 s
855 ms
829 vs
777 ms
735 s
719 vw
892 vw
876 ms
866 ms
824 s
803 s
682 s
661 s
609 s
583 s
525 s
452 s
682 ms, br
635 sh
557 sh
504 vs
473 sh
614 s
646 s
677 w
604 vw
572 w
530 vw
494 vw
447 s
729 vs
688 sh
656 vw
614 ms
583 ms
536 s
735 s
646 w
614w
530 vw
499 vs
467 s
Aromatic ring character of ortho
subtitution + NH2 def. + δb (CNO);
NO2
605 ms
572 w
462 ms
452 ms
619 ms
536 vs
452 ms
708 w
609 vw
577 vw
541 w
509 vs
494 w,sh
473 w
410 sh
431s
525 s 436 s
a
s = strong, w = weak, m = medium, sh = shoulder, v = very, br = broad
ν, stretching; δ, bending.
b

M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
785
Fig. 5. 1HNMR spectra of (A) o-tolidine; (B) p-toluidine; (C) DCQ; (D) DNB; (E) [(o-tolidine) (DCQ)]; (F) [(o-tolidine) (DNB)]; (G) [(p-toluidine) (DCQ)];
(H) [(p-toluidine) (DNB)] compounds in dmso, δTMS
.
for atoms attached with protons; therefore, the withdrawing
groups make decreasing in the electron density around pro-
tons and then consecutively increasing in the outer magnetic
field intensity which affect the nucleus. Therefore, the chemi-
cal transfer for these protons is higher than that of the protons
attached to the atom that have a lesser electron negativity. The
mentioned above mechanism was supported by the elemental
analysis, infrared spectra and the photometric titration which
make firm that the ratio occurs by 1:1 (donor:acceptor). The
1:1 molar ratio of (o-tolidine: DNB) has been interpreted by
using 1HNMR spectrum (Fig. 5, Scheme 1) which concluded
in the following mechanism:

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M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
The interaction between o-tolidine and DNB occurs
through one of the two amino groups in the donor and the
H-4 for DNB. The H-4 has more acidic character which
facilitates to make intermolecular hydrogen bond with one
of amino group because H-4 located in the ortho position
relative to two nitro groups (withdrawing group), which H-
4 became more easy to liberate. The other amino group is
attached with proton of the carboxylic group (intermolecular
hydrogen bond), this fact was supported beside photometric
titration (1:1 ratio) and elemental analysis. In terms of the
infrared spectra, the absence of the carboxylic group char-
acter and the disappearance of the value of ν(C O) of the
COOH group around 1700 cm−1, illustrated in the free
acceptor (DNB), were clearly indicated.
Concerning, the [(p-toluidine) (DCQ)] and [(p-toluidine)
(DNB)] the chemical shift in the amino group for both these
CT-complexes (δ 5.72 ppm and δ 5.25 ppm for [(p-toluidine)
Scheme 1. 1HNMR of (a) o-tolidine; (b) p-toluidine; (c) DCQ; (d) DNB; (e) [(o-tolidine) (DCQ)]; (f) [(o-tolidine) (DNB)]; (g) [(p-toluidine) (DCQ)]; (h)
[(p-toluidine) (DNB)] compounds in dmso, δTMS
.

M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
787
Scheme 1. (Continued ).

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M.S. Refat et al. / Spectrochimica Acta Part A 64 (2006) 778–788
(DCQ)] and [(p-toluidine) (DNB)] respectively) in the direc-
tion of downfield is caused by attachment of p-toluidine ring
by electron withdrawing groups. The displacement found in
the protons of benzene ring of p-toluidine to the downfield
direction lead us to make sure that this is attached with a
nucleus of electron withdrawing group. The chemical shift
of protons in DNB and DCQ towards upfield indicates that
these acceptors are attached to electron donating groups. The
interaction between p-toluidine and DCQ occurs through the
NH2 group and the H-3 or H-5 in DCQ in equal amounts.
On the other side the CT-complexation of p-toluidine with
DNB occurs between NH2 and COOH groups to form
intermolecular hydrogen bond as we discussed in Scheme 1.
Finally, we deduced that both of the o-tolidine and p-
toluidine reacts with various ␲-acceptors (DCQ and DNB)
in CHCl3 at room temperature to form stable CT-complexes
with molar ratio (1:1) although we used two different donors
one of them has one NH2 group and the other has two
NH2 groups. These results studied by using elemental anal-
ysis, electronic spectra, infrared spectroscopy, and 1HNMR
spectra.
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