Ultrasonic and spectroscopic studies on hydrogen bonded complexes of aromatic amine and aryl ketones in n-hexane at 303.15 K

Article abstract of DOI:10.1016/j.molliq.2011.07.010

Viscometric and ultrasonic studies have been carried out in n-hexane solutions, containing equimolar concentration from 0.02 to 0.2 M of aromatic ketones and N-methylaniline (NMANI), at 303.15 K and at atmospheric pressure. The ketones studied in the present investigation are acetophenone (ACP), 4-chloroacetophenone (ClACP) and 4-methylacetophenone (MACP). The behaviour of measured ultrasonic velocity (u), density (ρ) and viscosity (η) and also the computed acoustic parameters provide strong evidence for the presence of strong solute-solute interactions in the three ternary systems. Excess molar volume and excess thermo acoustic parameters reveal the existence of hydrogen bonded complexes between the solute molecules, ketones and secondary amine. The variation of these parameters with the concentration shows that the existing interactions are influenced by the structure of components and functional groups of the components involved. An attempt has been made to confirm the formation of 1:1 complexes in these systems through UV-visible spectroscopic method at 303.15 K. The calculated values of formation constants of the charge transfer complexes both by acoustic and optical methods agree satisfactorily. The variation in the values of formation constant reveals that electron releasing substituent in the acetophenone molecule enhances the stability while electronegative substituent decreases the stability of the complex. The negative values of free energy of formation of these three complexes indicate that these complexes are thermodynamically stable.

Full text of DOI:10.1016/j.molliq.2011.07.010

Journal of Molecular Liquids 163 (2011) 57–63
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Ultrasonic and spectroscopic studies on hydrogen bonded complexes of aromatic
amine and aryl ketones in n-hexane at 303.15 K
a
b
b
c
R. Kumar a, , N. Swarnalatha , R. Mahesh , B. Shanmugapriyan , V. Kannappan
⁎
a
Department of Physics, The New College, Chennai 600 014, India
Department of Physics, D. G. Vaishnav College, Chennai 600 106, India
Department of Chemistry, Presidency College, Chennai 600 005, India
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 May 2011
Received in revised form 13 July 2011
Accepted 19 July 2011
Available online 2 August 2011
Viscometric and ultrasonic studies have been carried out in n-hexane solutions, containing equimolar
concentration from 0.02 to 0.2 M of aromatic ketones and N-methylaniline (NMANI), at 303.15 K and at
atmospheric pressure. The ketones studied in the present investigation are acetophenone (ACP), 4-
chloroacetophenone (ClACP) and 4-methylacetophenone (MACP). The behaviour of measured ultrasonic
velocity (u), density (ρ) and viscosity (η) and also the computed acoustic parameters provide strong evidence
for the presence of strong solute–solute interactions in the three ternary systems. Excess molar volume and
excess thermo acoustic parameters reveal the existence of hydrogen bonded complexes between the solute
molecules, ketones and secondary amine. The variation of these parameters with the concentration shows
that the existing interactions are influenced by the structure of components and functional groups of the
components involved. An attempt has been made to confirm the formation of 1:1 complexes in these systems
through UV–visible spectroscopic method at 303.15 K. The calculated values of formation constants of the
charge transfer complexes both by acoustic and optical methods agree satisfactorily. The variation in the
values of formation constant reveals that electron releasing substituent in the acetophenone molecule
enhances the stability while electronegative substituent decreases the stability of the complex. The negative
values of free energy of formation of these three complexes indicate that these complexes are
thermodynamically stable.
Keywords:
H-bonded complex
Aromatic ketone
Secondary amine
Acoustic parameter
Solute–solute interaction
Stability constant
Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
1. Introduction
In the present investigation, three aromatic ketones, acetophenone,
4-chloroacetophenone and 4-methylacetophenone were mixed sepa-
Charge transfer interaction plays a vital role in various fields [1–3].
The interaction between polar groups such as carbonyl group of
ketones and amino group in non-polar environment is significant
in practical applications. Carbonyl group which is a part of several
biologically important molecules such as protein, lipids and hor-
mones, has electron deficient carbon that can function as electrophile.
The carbonyl oxygen is electron rich and it can form hydrogen bond.
Ketones can interact strongly with amines and alcohols due to the
presence of active hydrogen in these molecules. Thus, the formation of
donor–acceptor complexes can be expected between ketones and
primary and secondary amines. It is reported that amines can form
charge transfer complexes with ketones [4]. The formation of charge
transfer complexes of ketones with aniline in n-hexane [5] and iodine
monochloride with ethers in different solvents [6] by ultrasonic
method have been reported.
rately with equimolar concentrations of N-methylaniline in n-hexane.
The values of ultrasonic velocity (u), density (ρ) and viscosity (η) were
measured for these solutions at 303.15 K. From these values, acoustic
parameters and excess parameters were computed. The stability
constants of the donor–acceptor complexes were calculated using
Kannappan equation (ultrasonic method) and Benesi–Hildebrand
equation (optical method) at ambient temperature and the results
are discussed. The stability constant values were used to calculate free
energy of formation (ΔG) of these complexes. The results are inter-
preted in terms of molecular interactions between the components of
the system.
2. Material and methods
All compounds used in the present work were of Analar grade
samples and they were purified before use in accordance with the
procedure described elsewhere [7,8]. The estimated purity was
N99.8%. Ultrasonic sound velocities were measured in a single crystal
variable path ultrasonic interferometer operating at 2 MHz frequency
supplied by Mittal Enterprises, India, Model F81, at 303.15 K. The
⁎
Corresponding author. Tel.: +91 9444297498 (mobile).
E-mail address: kumss73@gmail.com (R. Kumar).
0167-7322/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2011.07.010

58
R. Kumar et al. / Journal of Molecular Liquids 163 (2011) 57–63
Table 1
The values of ultrasonic velocity u, density ρ, viscosity η, adiabatic compressibility κ, free length Lf, molar volume V, free volume Vf, interaction parameter α, Lenard Jones Potential
LJP and internal pressure πi for equimolar concentration ‘C’ of acetophenone and N-methylaniline in n-hexane at 303.15 K.
C
u/
ρ/
η/
κ/
Lf/
V/
Vf/
α
LJP/
πi/
(ms−1
)
(kgm−3
)
(10−4 Nsm−2
)
(npa−1
)
(A0)
10−4(m3 mol−1
)
10−7 (m3 mol−1
)
(Jmol−1
)
(102 Mpa)
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
1064.1
1065.9
1067.9
1070.3
1071.2
1072.5
1074.9
1076.5
1076.9
1078.4
672.1
673.1
674.1
677.0
677.7
679.1
680.9
682.4
683.3
685.1
3.394
3.392
3.406
3.478
3.451
3.450
3.460
3.515
3.519
3.507
1.314
1.308
1.301
1.289
1.286
1.280
1.271
1.265
1.262
1.255
0.7250
0.7232
0.7213
0.7182
0.7172
0.7156
0.7131
0.7112
0.7105
0.7086
1.284
1.285
1.285
1.281
1.282
1.281
1.280
1.279
1.279
1.278
5.028
5.058
5.053
4.926
5.002
5.025
5.031
4.936
4.942
4.989
−0.0024
−0.0033
−0.0037
−0.0033
−0.0057
−0.0073
−0.0068
−0.0078
−0.0109
−0.0119
4.914
4.974
5.042
5.123
5.154
5.199
5.282
5.338
5.352
5.405
2.489
2.484
2.484
2.510
2.496
2.493
2.494
2.511
2.510
2.504
instrument was calibrated by measuring the velocity of triple distilled
water, carbon tetra chloride and dimethyl sulfoxide. The sound ve-
locities are accurate to 0.02%. The densities of the solutions were
determined using a 10 ml specific gravity bottle and a digital balance
of accuracy 10−6 kg. Viscosity measurements were made with an
Ostwald's viscometer in which the flow time for solutions was mea-
sured through a digital stop clock of accuracy 0.01 s. Digitally con-
trolled and well-stirred thermostatic water bath with a temperature
T=(303.15 0.1) K was used for all the measurements. UV–visible
spectra were recorded on a Shimadzu UV-1650 model spectrophotom-
eter with quartz cell of 1 cm optical path length. The solvent (n-hexane)
was used for base line correction. The absorbance spectra were recorded
in the region of 200–700 nm at a scanning rate of 0.2 nm/s and a slit
width of 1 cm.
The standard relations used to calculate the various acoustic and
excess thermo acoustic parameters using the measured values of
ultrasonic velocity (u), density (ρ) and viscosity (η) were taken from
literature [9–11]. The stability constants of the complexes were com-
puted from ‘u’ values by employing Kannappan equation and using
the absorbance values of UV–vis spectra by employing Benesi–
Hildebrand equation as reported in our earlier work [12].
3. Results and discussion
3.1. Acoustical parameters
The measured values of ultrasonic velocity (u), density (ρ)viscosity
(η) and the computed values of various acoustic parameters for the
three ternary systems at 303.15 K are presented in Tables 1–3. The
variation of adiabatic compressibility (κ) and internal pressure (πi) with
concentration of amine and ketones (equimolar) are shown in Figs. 1
and 2. Perusal of Tables 1–3 reveals that the measured parameters for
the three ternary systems increase with the increase in the solute
concentrations. The trend in the ultrasonic velocity is almost similar
for all the systems. The increase in velocity may be attributed to strong
solute–solute interactions. It was reported that the strength of mo-
lecular interaction in liquid mixtures becomes maximum where the
velocity maxima occur [13]. This may probably be due to molecular
association and complex formation through hydrogen bonding[14]. The
mixing of ketones, with secondary amine, N-methylaniline breaks the
hydrogen bonds in NMANI releasing several molecules of the com-
ponent liquids for mutual interaction, possibly through (new) hydrogen
bonds between –COCH3 group of ketone with –NHCH3 group of NMANI.
Table 2
The values of ultrasonic velocity u, density ρ, viscosity η, adiabatic compressibility κ, free length Lf, molar volume V, free volume Vf, interaction parameter α, Lenard Jones Potential
LJP and internal pressure πi for equimolar concentration ‘C’ of 4-chloroacetophenone and N-methylaniline in n-hexane at 303.15 K.
C
u/
ρ/
η/
κ/
Lf/
V/
Vf/
α
LJP/
πi/
(ms−1
)
(kg m−3
)
(10−4 Nsm−2
)
(npa−1
)
(A0)
10−4 (m3 mol−1
)
10−7 (m3 mol−1
)
(Jmol−1
)
(102 Mpa)
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
1064.5
1066.6
1068.0
1069.5
1071.1
1072.6
1074.2
1075.4
1077.4
1078.9
671.2
673.6
677.0
678.5
681.0
683.1
684.8
687.1
689.1
691.2
3.379
3.447
3.445
3.479
3.516
3.508
3.525
3.553
3.567
3.604
1.315
1.305
1.295
1.289
1.280
1.272
1.266
1.258
1.250
1.243
0.7252
0.7225
0.7197
0.7179
0.7155
0.7134
0.7115
0.7095
0.7072
0.7051
1.287
1.286
1.283
1.284
1.282
1.282
1.282
1.280
1.280
1.279
5.073
4.958
4.991
4.948
4.900
4.946
4.940
4.908
4.910
4.862
−0.0015
−0.0016
−0.0029
−0.0040
−0.0049
−0.0060
−0.0068
−0.0083
−0.0083
−0.0092
4.927
4.998
5.045
5.096
5.151
5.203
5.258
5.300
5.370
5.423
2.478
2.498
2.497
2.503
2.513
2.506
2.507
2.514
2.515
2.524
Table 3
The values of ultrasonic velocity u, density ρ, viscosity η, adiabatic compressibility κ, free length Lf, molar volume V, free volume Vf, interaction parameter α, Lenard Jones Potential
LJP and internal pressure πi for equimolar concentration ‘C’ of 4-methylacetophenone and N-methylaniline in n-hexane at 303.15 K.
C
u/
ρ/
η/
κ/
Lf/
V/
Vf/
α
LJP/
πi/
(ms−1
)
(kg m−3
)
(10−4 Nsm−2
)
(npa−1
)
(A0)
10−4 (m3 mol−1
)
10−7 (m3 mol−1
)
(Jmol−1
)
(102 Mpa)
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
1064.7
1066.2
1068.0
1069.6
1071.7
1073.4
1075.1
1076.6
1078.8
1080.6
668.9
671.1
672.8
674.1
676.2
678.0
679.9
681.6
682.9
685.4
3.379
3.447
3.445
3.479
3.516
3.508
3.525
3.553
3.567
3.604
1.319
1.311
1.303
1.297
1.288
1.280
1.272
1.266
1.258
1.249
0.7263
0.7241
0.7220
0.7202
0.7177
0.7156
0.7134
0.7116
0.7094
0.7070
1.292
1.289
1.289
1.289
1.287
1.287
1.285
1.285
1.285
1.282
5.074
4.946
4.978
4.931
4.882
4.925
4.915
4.881
4.881
4.832
−0.0013
−0.0027
−0.0035
−0.0046
−0.0048
−0.0057
−0.0065
−0.0076
−0.0074
−0.0079
4.934
4.984
5.045
5.100
5.171
5.230
5.289
5.342
5.419
5.483
2.472
2.496
2.492
2.499
2.509
2.503
2.506
2.513
2.513
2.525

R. Kumar et al. / Journal of Molecular Liquids 163 (2011) 57–63
59
packing, resulting in a decrease of free length ‘Lf’ [15]. The constant
values of molar volume for all the three systems identify that the
components are of comparable size and also there may not be any
greater structural changes by the addition of both the solutes in the
solvent n-hexane.
The plot of internal pressure against concentration of carbonyl
compound or amine shows that as the concentration increases πi
value increases. A reverse trend, as expected, is observed in the var-
iations of free volume (Vf) (Tables 1–3) [16]. The increase in the
values of internal pressure with concentration at the temperature
investigation clearly explains the growing molecular association
through stronger type of interaction against thermal agitation of
molecules. The decreasing trend of Vf suggests the tightly bound
system of molecules inside the shield, which may be brought about by
the growing magnitude of solute–solute interaction. The trend in the
values of free volume with concentration supports the trends ob-
served for ‘κ’ and ‘Lf’.
The magnitude of LJP is almost constant for all the systems and also
at all concentrations. The magnitude of LJP indicates the presence of
intermolecular hydrogen bonding in the ternary systems. Molecular
interaction parameter in a system is a measure of deviation from
ideal behaviour and hence it gives the strength of molecular interac-
tion in binary and ternary systems. The negative values of interaction
parameter also reveal the presence of strong interactions between
carbonyl compounds and NMANI.
Fig. 1. Plotof adiabatic compressibility versus equimolar concentration of N-methylaniline
and three ketones in n-hexane solution at 303.15 K.
3.2. Excess parameters
The computed values of excess parameters such as, excess free
length (LEf ), excess molar volume (VmE ) and excess free volume (VfE)
are listed in Table 4. Plots of variation of excess velocity (uE), excess
compressibility (κE) and excess internal pressure (πiE) against
concentration are shown in Figs. 3–5. The negative values in excess
ultrasonic velocity (uE) explain the non-ideal nature of these three
ternary liquid mixtures and greater deviations suggest stronger
magnitude of intermolecular interactions between the component
molecules. The growing interactions with concentration, the disruption
of the like molecular interactions by the addition of solutes and the
formation of tightly bound systems are also revealed by the uniform
decrease in the excess velocity. It may be pointed out that the excess
velocity is more negative in the case of 4-methylacetophenone —
NMANI system suggesting that the interactions may be stronger
between the ketone and amine in this system.
Fig. 2. Plot of internal pressure versus equimolar concentration of N-methylaniline and
three ketones in n-hexane solution at 303.15 K.
However, the strength of interaction between the components of
the mixtures is influenced by the nature of substituent groups present in
the solute molecules due to polar effects.
As expected, the adiabatic compressibility and free length show a
reverse trend as that of ‘u’ and ‘ρ’. A continuous decrease in adiabatic
compressibility (κ) and intermolecular free length (Lf) is a supporting
evidence for the existence of strong interactions in the liquid mixtures
which lead to the increasing compactness of the systems. The rapid
decrease of ‘κ’ indicates the formation of a large number of tightly
bound systems. Such a reduction in ‘κ’ brings the molecules to a close
The magnitude of excess compressibility is less compared to
adiabatic compressibility values. It may be due to the mutual repulsion
between the π-electrons of the aromatic rings of amines and ketones
[17]. The negative values of these parameters can be explained by the
formation of hydrogen bonding and complex formation between the
components [18]. The degree of compactness is increasing as indicated
by increasingly negative values of κE.
Table 4
Excess free length LfE, excess molar volume VE, and excess free volume VfE for equimolar concentration ‘C’ of ketones with N-methylaniline in n-hexane at 303.15 K.
C
Acetophenone
4-chloroacetophenone
4-methylacetophenone
LEf /
VE/
VfE/
LfE/
VE/
VfE/
LfE/
VE/
VfE/
(10−13 m)
(10−6 m3 mol−1
)
(10−8 m3 mol−1
)
(10−13 m)
(10−6 m3 mol−1
)
(10−8 m3 mol−1
)
(10−13 m)
(10−6 m3 mol−1
)
(10−8 m3 mol−1
)
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
−7.130
−7.285
−7.583
−9.170
−8.586
−8.649
−9.665
−9.994
−9.231
−9.669
−2.568
−2.459
−2.353
−2.611
−2.454
−2.432
−2.488
−2.490
−2.383
−2.446
1.171
1.654
1.791
0.696
1.638
2.048
2.292
1.514
1.742
2.385
−6.870
−7.927
−9.043
−9.222
−10.00
−10.51
−10.88
−11.30
−12.10
−12.62
−2.293
−2.351
−2.602
−2.496
−2.583
−2.597
−2.540
−2.598
−2.604
−2.631
1.634
0.697
1.233
1.001
0.19
1.377
1.511
1.386
1.605
1.317
−5.825
−6.439
−6.991
−7.203
−8.184
−8.737
−9.351
−9.730
−0.103
−0.113
−1.862
−2.053
−2.070
−2.014
−2.114
−2.158
−2.225
−2.255
−2.214
−2.400
1.631
0.537
1.045
0.761
0.456
1.067
1.150
0.989
1.166
0.846

60
R. Kumar et al. / Journal of Molecular Liquids 163 (2011) 57–63
Fig. 3. Plot of excess velocity versus equimolar concentration of N-methylaniline and
three ketones in n-hexane solution at 303.15 K.
Fig. 5. Plot of excess internal pressure versus equimolar concentration of N-
methylaniline and three ketones in n-hexane solution at 303.15 K.
The excess free length (LfE) for the ternary systems of NMANI with
ketones in n-hexane shows a low negative deviation. Though the
strength of interaction is more, the low values of LfE identify that
there are no structural changes in the components of the system. The
low negative deviations of both κE and LfE also indicate the absence
of interstitial accommodation of unlike molecules because of the
comparable size of the components in the mixtures. The low values in
these two parameters may be attributed to the dispersive interactions
and the breaking of dipole–dipole order between unlike molecules at
lower concentration and specific interactions between unlike mole-
cules in the mixture leading to the formation charge transfer
complexes at higher concentrations [19,20]. The rupture of dipolar
association of like molecules and formation of strong complexes
between unlike molecules may be the reason for increasing negative
values of LfE.
The sign and magnitude of excess molar volume may arise due to
i) mutual loss of dipolar or self association due to addition of second
component and contributions due to difference in the size and shape
of the molecules and ii) strong interactions such as dipole–dipole,
hydrogen bonding or complex formation between unlike molecules.
The first factor contributes to expansion in volume and second factor
contributes decrease or contraction in volume. The experimental
results of VmE for all the three ternary systems in the present inves-
tigation suggest that the factors which are responsible for contraction
in volume are dominant [21].
The variation of excess pressure (πiE) values is exactly reverse to
that of excess free volume. The reverse trend in these two param-
eters and the negative deviation in internal pressure is an indication
of stronger adhesion between the components in the mixture as
reported [22]. The presence of many peaks πiE in the concentration
range under investigation and different behaviour of πiE for different
systems clearly confirm that the functional group of ketone plays a
vital role since the geometry of molecular systems is almost the same
for all the systems. As in the case of VmE , the sign of VfE depends upon
the relative strength between the contractive forces and expansive
forces. Though the strength molecular association of solute mol-
ecules dominates, the combined effect of rupture of like molecular
association, dispersive forces in the solvent molecules, the absence of
geometrical fitting of unlike molecules due to same size of com-
ponents in the systems and electrostatic repulsion between the π-
electrons of aromatic solute molecules, lead to positive deviation in
free volume [23].
3.3. UV–vis spectral studies
As a part of confirmation for the formation of charge transfer
complexes between aromatic ketones and aromatic amine in n-
hexane medium, UV–vis spectra were recorded for the three ternary
systems. The recorded absorbance spectra at 303.15 K have been
depicted in Figs. 6–8. The Benesi–Hildebrand equation is applicable on
the experimental condition that either donor or acceptor concentra-
tion should be present in large excess [24,25]. In the present in-
vestigation, the concentration of acceptor N-methylaniline was kept
constant at 5×10−6 M and the concentration of donor, ketones,
was varied in excess. It was observed that there was a shift in the
frequencies in the spectra of complexes from the spectra of pure
compounds and also the absorbance is quite high than pure spectra.
This clearly reveals the formation of strong complexes between
amines and ketones [26–28]. From Figs. 6–8, it is observed that
there is one strong and broad charge transfer bands appear for all the
three systems. The maximum absorption is observed at 238.4 nm,
248.6 nm and 246.6 nm for acetophenone, 4-chloroacetophenone
and 4-methylacetophenone respectively. The intensities of the CT
bands at maximum wavelength of absorptions increase with the in-
crease in the concentration of ketones. The shift in the maximum
wavelength (λmax) of CT bands may be attributed to the difference in
the strength of complexation between the donor and the acceptor.
Fig. 4. Plot of excess compressibility versus equimolar concentration of N-methylaniline
and three ketones in n-hexane solution at 303.15 K.

R. Kumar et al. / Journal of Molecular Liquids 163 (2011) 57–63
61
Fig. 6. Recorded UV–vis spectra for the variation of wavelength λ versus absorbance for
N-methylaniline and acetophenone in n-hexane medium at 303.15 K. The concentra-
tion of acceptor amine was kept constant at 5×10−6 M and the concentration of donor,
ketones, was varied in excess.
Fig. 8. Recorded UV–vis spectra for the variation of wavelength λ versus absorbance for
N-methylaniline and 4-methylacetophenone in n-hexane medium at 303.15 K. The
concentration of acceptor amine was kept constant at 5×10−6 M and the concentration
of donor, ketones, was varied in excess.
3.4. Thermodynamic parameters
The thermodynamic stability of the donor–acceptor complexes
formed between the ketones and amine can be compared by
determining the stability constants of these complexes. The values
of stability constant were calculated at 303.15 K for each system by
applying Kannappan Equation (acoustic method) from the measured
values of ultrasonic velocity. These values at ambient temperature
were calculated by employing Benesi–Hildebrand (BH) equation
(optical method) with the observed values of optical absorbance of
UV spectra. These results along with free energy of formation (ΔG),
relaxation time (τ), maximum absorption wavelength (λmax) and
molar absorptivities (εmax) are listed in Table 5. The BH plots for the
determination of formation constant (K) and the molar extinction
coefficient (ε) of charge transfer complexes by optical method are
shown in Fig. 9.
The BH plots obtained for the charge transfer complexes were found
to be linear with a positive slope and intercept. A linear BH plot is an
indication of the formation of 1:1 complexes between primary amine
and ketones [29,30]. The structure of amines as well as ketones deter-
mines the formation constant of the complexes. Carbonyl compounds
are weakly associated liquids in pure state due to dipole–dipole inter-
action but they are strongly associated with other components like
amines in the mixture through strong hydrogen bonded complex for-
mation between carbonyl oxygen of ketone and the hydrogen atom of
imino group of NMANI as shown in Fig. 10.
The stability constant of the hydrogen bonded complexes in-
creases in the order 4-chloroacetophenonebacetophenoneb4-methyl
acetophenone. As the complexation occurs between carbonyl oxygen of
ketone and hydrogen of imino group in N-methylaniline, the stability of
the complex is influenced on the availability of electrons on carbonyl
oxygen and nitrogen of amino group. The presence of electron releasing
methyl group in the acetophenone enhances the nucleophilic character
Fig. 7. Recorded UV–vis spectra for the variation of wavelength λ versus absorbance for
N-methylaniline and 4-chloroacetophenone in n-hexane medium at 303.15 K. The
concentration of acceptor amine was kept constant at 5×10−6 M and the concentration
of donor, ketones, was varied in excess.

62
R. Kumar et al. / Journal of Molecular Liquids 163 (2011) 57–63
Table 5
⁎
Stability constant K, free energy of formation ΔG , relaxation time τ, wave length of maximum absorption λmax and molar extinction coefficient ε for various aromatic ketones with
N-methylaniline in n-hexane medium obtained by ultrasonic and UV–Vis. Spectrometric techniques at 303.15 K.
Solvent: n-hexane
Donor
Acceptor: N-methylaniline
Temperatures: 303.15 K
Ka
ΔG
/
τa/
Kb
ΔG
/
λmax
/
εb/107
a
b
b
⁎
⁎
(kJ mol−1
)
(10−12 s)
(kJ mol−1
)
(nm)
Acetophenone
4-chloroacetophenone
4-methylacetophenone
142.67
122.04
198.59
−12.50
−12.11
−13.34
5.913
5.963
5.996
217.43
167.25
263.32
−13.56
−12.90
−14.05
238.4
248.6
246.6
1.354
1.852
1.231
a
Ultrasonic technique.
Spectroscopic technique.
b
4. Conclusions
The present investigation deals with study of the molecular
interaction of aromatic amine, N-methylaniline with aromatic ketones
in the non-polar medium, n-hexane by ultrasonic and UV–vis spectral
methods. The extensive investigation clearly establishes the existence of
hydrogen bonded complex formation between these two solute
molecules. The behaviour of the calculated values of formation constant
reveals the influence of functional groups on the acetophenone
molecule on the stability of the complexes formed. The formation
constant values computed by ultrasonic and optical methods indicate
that the stability of the complex is in the order:
4-Methylacetophenone–NMANI NAcetophenone–NMANI N4-
Chloroactophenone–NMANI. The negative values of free energy of
formation of these three complexes indicate that these complexes are
thermodynamically stable.
Acknowledgements
Fig. 9. Benesi–Hildebrand plots for N-methylaniline with ketones in n-hexane solutions
at 303.15 K.
The authors thank the Management of The New College, Chennai
600 014, India for the facilities provided to us during the course of this
work.
of carbonyl oxygen and thus favours complex formation in the case of
4-methylacetophenone through strong hydrogen bond formation.
However, in the case of 4-chloroacetophenone the presence of electron
withdrawing group near the carbonyl group weakens the hydrogen
bond. This is indicated by the smaller value of ‘K’ for this complex.
The intrinsic behaviour of the complexes formed, may be ob-
served through the constant values of relaxation time (τ). The same
values of ‘τ’ for all systems suggest that similar type of complexes is
formed between ketones and amines. The very high values of molar
extinction coefficient (ε) determined by optical method reveal that
References
[1] S. Sadeghi, E. Karimi, Chem. Pharm. Bull. 54 (2006) 1107–1112.
[2] H. Kusama, H. Sugihara, J. Photochem. Photobiol., A 181 (2006) 268–273.
[3] K. Bradley, M. Briman, A. Star, G. Gruner, Nano Lett. 4 (2004) 253–256.
[4] K.K. Gupta, A.K. Bansal, P.J. Singh, K.S. Sharma, Indian J. Pure Appl. Phys. 79 (2005)
147–152.
[5] V. Kannappan, N. Indra Gandhi, Phys. Chem. Liq. 46 (2008) 510–521.
[6] V. Kannappan, S.J. Askar Ali, P.A. Abdul Mahaboob, Indian J. Pure Appl. Phys. 47
(2009) 97–102.
[7] A.I. Vogel, A Textbook ofPracticalOrganic Chemistry, 5th Edn. John Willey, New York,
1989.
[8] A. Weissberger, F.S. Prokaher, J.A. Reddick, E.E. Toops, Techniques of Organic
Chemistry, Organic Solvents, Vol VII, Interscience, New York, 1955.
[9] V. Baldevraj, Rajendran, Palanichamy, Science and Technology of Ultrasonics,
Narosa Publishing House, New Delhi, 2004.
[10] R. Kumar, S. Jayakumar, V. Kannappan, Ind. J. Pure Appl Phys. 46 (2008) 169–175.
[11] R. Mehra, M. Pancholi, Indian J. Phys. 80 (2006) 253–263.
[12] V. Ulagendran, R. Kumar, S. Jayakumar, V. Kannappan, J. Mol. Liq. 148 (2009)
67–72.
[13] Isht Vibhu, Avneesh K. Singh, Manisha Gupta, J.P. Shukla, J. Mol. Liq. 115 (2004) 1–3.
[14] A. Awasthi, M. Rastogi, M. Gupta, J.P. Shukla, J. Mol. Liq. 80 (1999) 77.
[15] L. Palaniappan, Physica B 403 (2008) 3887–3891.
⁎
⁎
the complexation may be due to both π→π and n→π types of
interactions [31].
The free energy of formation (ΔG) follows the same trend as that of
the stability constant values. The negative values of free energy of
formation reveal that the charge transfer interaction is exothermic. It
is found from the table that the systems with 4-methylacetophenone
appear to be more exothermic and 4-chloroacetophenone less
exothermic.
[16] A.N. Kannapan, R. Kesavasamy, V. Ponnuswamy, J. Eng. Appl. Sci. 3 (4) (2008)
41–45.
[17] K.V.N. Suresh Reddy, P. Srinivasa Rao, A. Krishnaiah, J. Mol. Liq. 135 (2007) 14–20.
[18] L. Mosteiro, L.M. Casas, J.L. Legido, J. Chem. Thermodyn. 41 (2009) 695.
[19] S.L. Oswal, R.L. Gardas, R.P. Phalak, J. Mol. Liq. 116 (2005) 109–118.
[20] A. Ali, A.K. Nain, V.K. Sharma, S. Ahmad, Phys. Chem. Liq. 42 (2004) 375–383.
[21] P. Gnanakumari, P. Venkatesu, M.V. Prabhakara Rao, Ming - Jer Lee, Ho - mu Lin,
J. Chem. Thermodyn. 41 (2009) 586–590.
[22] R. Thiyagarajan, Jaafar Mohamad Suhaimi, L. Palaniappan, J. Phys. Sci. 18 (2007) 81–88.
[23] R. Palani, S. Balakrishnan, Indian J. Pure Appl. Phys. 48 (2010) 644–650.
[24] H.A. Benesi, J.H. Hildebrand, J. Am. Chem. Soc. 71 (1949) 2703–2707.
[25] Hulya Duymus, Mustafa Arslan, Mustafa Kucukislamoglu, Mustafa Zengin,
Spectrochim. Acta, Part A 65 (2006) 1120–1124.
Fig. 10. Possible mechanism for the formation of hydrogen bonding between carbonyl
group of ketone with the imino group of N-methyl aniline.

R. Kumar et al. / Journal of Molecular Liquids 163 (2011) 57–63
63
[26] R.S. Mulliken, W.B. Pearson, Molecular Complexes, Wiley Publishers, New York,
1969.
[27] R. Foster, Charge-transfer Complexes, 51, Academic Press, London, 1969, p. 387.
[28] H.M.A. Salman, M.M. Abu – Krisha, H.S. El – Sheshtawy, Can. J. Anal. Sci. Spectros.
49 (2004) 282–289.
[29] R. Foster, Molecular Complexes, Vol. 1, Science, London, 1973.
[30] M.S. Refat, S.M. Aqeel, I.K. Grabtchev, Can. J. Anal. Sci. Spectros. 49 (2004)
258–265.
[31] J. Mohan, Organic Spectroscopy: Principle and Applications, II Edn. Narosa
Publishing House, India, 2004.