Materials Sciences and Applicatio ns, 2011, 2, 503-508
doi:10.4236/msa.2011.26068 Published Online June 2011 (
Copyright © 2011 SciRes. MSA
Influence of Benzoate on Substituent Benzoic Acids
with Implications on Spectroscopic Studies
through Inter Molecular Hydrogen Bonding
Ch.Ravi Shankar Kumar
Department of Physics, Institute of Science, GITAM University, Visakhapatnam, India.
Received March 11th, 2011; revised April 20th, 2011; accepted May 20th, 2011.
Comprehensive study on the homologous series of compounds in the form A-R-HHB are synthesized with central rigid
core as benzoic acids together with substituents alkoxy (A) and alkyl (R) group of equal chain lengths from 5 to 10 are
connected to hexyl-p-hydroxy benzoate (HHB). These complexes form supramolecular structures by self assembling
process due to intermolecular hydrogen bonding. The formation is analyzed with techniques involving polarizing opti-
cal microscope, infrared spectroscopy, proton NMR spectroscopy and powdered X-ray diffraction. Results suggest that
complexes arise from both A and R groups exhibit enantiotropic layered texture of crystal G phase observed by micro-
scopic studies due to flexible nature of mesogenics. The conversion of free to molecular complexes is determined with
variations in spectral shifts between its terminal groups COOH and OH of molecules involving inter molecular hydro-
gen bonding and its bonding index by FTIR spectra. The changes in structure and dynamics due to hydrogen bonding in
complexes are convinced by proton NMR spectra with chemical shifts in specified range. The defects in crystal struc-
ture responsible for enantiotropic phenomena are analyzed by powdered X-ray diffraction.
Keywords: Phase Transitions, Microscopy, IR Spectra and Hydrogen Bonding
1. Introduction
Over the past decades the design and synthesis of new
liquid crystalline molecules [1] has considerably broad-
ened mesophase stability [2]especially with rod like mo-
lecules due to intermolecular interactions [3,4] that play
vital role in the formation of liquid crystal textures [5].
These organized structures are built by strategic units
leading to supramolecular structures [6,7] enable mean-
ingful relationship cutting across its entities with their
functional relationships attributed involves hydrogen
bonding [8]. Liquid crystals possess fluid like properties
are greatly influenced with non mesogenics stems the
interaction leading to structural variations by self assem-
bling [9-13] process that greatly influence the physical
properties due to defects that exist in solid state where
individual displacements of atoms are suppressed. The
substituent liquid crystals or mesogenics exhibiting ne-
matics under consideration are perfectly rigid [8,11,14]
when associated with addition of benzoate (HHB) results
with deviation in structure that occur due interaction be-
tween molecules. Many investigations lead to the forma-
tion of supramolecular structures due to hydrogen bond-
ing due to its stability [2,15] and directionality that sig-
nificantly change the molecules has drawn attention in
development of new structures. In the present work me-
somorphic properties [16] emphasized in terms of its
features in normal state between hexyl-p-hydroxy benzo-
ate and substituent liquid crystals A [17] and R [18]
through hydrogen bon ding as illustrated in Figure 1.
2. Experimental
The two mesogenics [19] that were chosen for conduct of
experimental studies include the p-n-alkoxy benzoic acid
(A), p-n-alkyl benzoic acid (R) and non mesogenic hexyl-
p-hydroxy benzoate (HHB) are purchased from Frinton
laboratories New Jersey, USA. These compounds possess
a number of favorable properties in studies involving
both crystalline and aniso tropic states. The preparation is
performed by dissolving in 1:1 ratio the compounds in
pyridine under constant stirring for about 4 hours ap-
proximately at 80˚C and the clear solution is obtained.
The solvent was removed by fractional distillation with
Influence of Benzoate on Substituent Benzoic Acids with Implications on Spectroscopic
504 Studies through Inter Molecular Hydrogen Bonding
resultant mixture was dried and re-crystallized by using
The phase transition temperatures and texture studies
of synthesized materials were studied using Hertel Reuss
super-pan II polarizing optical microscope (POM)
equipped with optical display (DP10) at scan rate of
0.1˚C/min. The liquid state (chloroform) and solid state
(KBr) FT-IR-spectra were recorded on Perkin-Elmer
(spectrum bX) series at room temperature from 400 -
4400 cm–1 with resolution 8 cm–1. The proton nuclear
magnetic resonance (1H NMR) spectra were recorded on
the Brucker Avance 400 MHz instrument in CDCL3 with
chemical shifts in ppm. X-ray studies were performed at
room temperature using Phillips powdered XRD system
in determining crystalline parameters.
3. Results and Discussions
Liquid crystals show unusual behavior due to variations
in temperature. The transitions from crystalline to iso-
tropic and back occur in single step in both heating and
cooling process. Textures observed by polarizing optical
microscope obtained in heating are much difficult to as-
sign as they are complicated and natural textures in
cooling are significant, of substituent’s A and R and its
complexes A-R-HHB are listed in Table 1. Realization
of complexes by self assembling lead to supramolecular
structures possess mechanical properties better than con-
ventional liquid crystals by extending its flexible ends [19-
21] with benzoate that gained positional order with lay-
ered texture of crystal G phase as illustrated in Figure 2.
This phase has molecules packed in layers with their
long axis tilted with respect to normal to layer planes
with tilt molecules performing reorientational motion
about long axes that contributes to hexagonal symmetry
A consequence of transition temperatures of the free and
complexes is that oriertational textures with long axes of
molecules perpendicular to glass substrate involve higher
transition temperatures than layered textures where long
axes are at an angle with glass substrate. The transition
temperatures are plotted against chain length are illus-
trated in Figure 3. The lowered nature of temperatures is
an implication of lose in rigidity, reducing fluidity and
change in symmetry of free molecules due to participa-
tion of flexible ends with benzoates with thermal span
lesser by 8˚C. A feature in transition temperatures of
molecular complexes associates contrast behavior in
members of substituent’s A and partial even odd effect
[22] with R group that reveal the length of flexible ter-
minals had influenced in occurrence of the said phase.
The Fourier transform infrared spectral interpretation
[23-25] is used in exploiting the structural defects re-
sponsible for change in orientation is realized with spec-
tral shifts (cm–1) due to hydrogen bonding (OH) of sub-
stituent’s and its complexes are listed in Table 2. The
solid state spectral studies reveal OH of A and R groups
is much less in comparison with HHB indicating their
intact nature. On complexation there is tremendous
change in spectral shifts of complexes A-R-HHB formed
with A are contrary with R group. On structural level
these shifts enabled terminal groups of aromatic rings to
participate in hydrogen bonding that has nucleated in
formation of layered texture.
Figure 1. Bonded structure of substituted benzoic acid with hexyl-p-hydroxy benzoate.
Table 1. Polarizing optical microscope studies of free and complexes.
Type of texture Transition Temperatures ˚C
Chain Length A R (A-R-HHB)A R (A-R-HHB)A(A-R-HHB)R
5 N N G 151.4 124 98.4 96
6 N N G 153.8 112.5 85 71
7 N N G 146.8 121.7 80 83.5
8 N N G 147.5 110.3 85.7 83
9 N N G 142.9 115.8 87.2 83
10 N N G 138.3 108.8 90.6 81.4
Copyright © 2011 SciRes. MSA
Influence of Benzoate on Substituent Benzoic Acids with Implications on Spectroscopic 505
Studies through Inter Molecular Hydrogen Bonding
Figure 2. Texture of crystal G phase.
Figure 3. Plot of transition temperatures vs chain length.
Coordinating the absorption studies from FTIR spectra
of substituent’s and complexes in determination of hy-
drogen bonding index [26,27] responsible for altered
texture are listed in Table 3. These absorption studies
reveal even odd behavior in substituent groups A and R
that is lost on complexation with benzoate. The studies
involving hydrogen bonding index determines the extent
of participation between the molecules that increases
slowly in chain length with A group due to paramorpho-
sis and an even odd behavior associates with R group.
These variations signify that flexible terminals of both
groups influenced the occurrence of phase due to dis-
persed non covalent interaction .
The studies of complexes with NMR spectra [28] pro-
vide rich structure and dynamic information that is lost
due to its swift averaging in the liquid phase. Chemical
shifts provide the first signature to understand the pack-
ing and hydrogen bonding formation [29] in the solid
state. The 1H NMR spectra of the free and its complexes
exhibit different regions are well resolved in the spec-
trum. The structural studies for complexes indicate
chemical shifts around 0.9 attributed to the CH3, multi-
plets in range 1.3 - 1.8 attributes to (CH2)n of both the
groups and 4.3 triplet for bonded OH. The shifts at 6.9 -
7.0 contribute to aromatic protons. The OH of phenolic is
assigned to 8.2 suggests the down field shift due to inter
molecular hydrogen bonding These chemical shifts re-
veal the convinced IR with peak aroun d 680 - 730 cm–1.
Finally with X-ray diffraction [30] involving small an-
gle regions reveal the information of the anisotropic
properties between parallel and perpendicular incident
directions. These properties arise due to defects existing
in solid state which are the crystalline parameters deter-
mined in angstrom units (AU) are listed in Table 4.
The inter planar spacing d = nλ/sinθ, the thickness (t) =
0.94 λ/(BcosθB) are determined with λ = 1.54056 ang-
stroms units, (B) is full width half maximum and θB is
bragg angle. The studies reveal drastic change in inten-
sity, interplanar spacing and thickness irrespective of the
substituent group in comparison with the benzoate. The
influence of fun ctional molec ules is integrated into system
by involving the crystalline properties for the obtained
texture with reduced scattering. The choice of benzoate
enabled in generation of new molecular structure that
helped to expand the properties of liquid crystals that
arise from aromatics due to displaced center of gravities
with increased variation in size and planar separation.
With increase in chain length the influence of benzoate
on the core molecule enabled greater degree of confor-
mational freedom [31,32]. These parameters articulate
that the benzoate group has successfully disturbed the
oriented texture of its molecules to layered texture.
4. Conclusions
The work resulted in influence of benzoate successfully
leading with enantio tropic layered textur e in both alkoxy
and alkyl groups. The disturbed symmetry with reduced
transition temperatures gained positional order by self
assembling process. The hydrogen bonding with narrow
peaks and enhanced shifts lead the aromatic rings to nu-
cleate its structure together with bonding index has in-
creased molecular packing. The liquid crystal on com-
plexation with benzoate has lead to new molecular and
supramolecular structure with properties that are de-
pendent of aromatics that ar e mesogens. The explanation
is valid with necessary support in alterin g the texture and
its confirmation with various techniques due to hexyl-p-
hydroxy benzoate and further studies in control of self
ssembling process need to be performed. a
Copyright © 2011 SciRes. MSA
Influence of Benzoate on Substituent Benzoic Acids with Implications on Spectroscopic
506 Studies through Inter Molecular Hydrogen Bonding
Table 2. Solid state IR spectra.
Chain Length (OH)A (OH)R (OH)HHB (A-R-HHB)OHA (A-R-HHB)OHR
5 2955 2958 3300 3294
6 2933 3120 3435 3439
7 2932 2926 3441 3297
8 3130 2926 3399 3295
9 2924 2924 3412 3440
10 2923 2923 3389 3395
Table 3. Hydrogen bonding index.
Chain Length (OH)A (OH)R (A-R-HHB)A(Bonding index)A(A-R-HHB)R(Bonding index)R
5 65.76 19.93 14.56 0.221 20.67 1.037
6 28.07 70.07 30.89 1.100 24.1 0.343
7 72.19 19.38 84.77 1.174 26.20 1.351
8 35.07 37.47 69.04 1.968 26.76 0.714
9 37.26 11.75 91.72 2.461 21.75 1.851
10 33.07 16.75 96.6 2.9210 25.10 1.498
Table 4. Crystalline parameters.
Name of Compound Bragg angle Intensity Interplanar distance Thickness
HHB 22.657 224 3.999 0.0767
5 20.053 473 4.4918 0.765
6 23.008 789 3.9407 3.7004
7 14.194 2731 6.2828 1.829
8 20.024 1146 4.499 0.7356
9 9.577 148 9.258 0.0394
10 4.449 98 19.86 0.3800
5 12.285 582 7.2404 1.1013
6 22.810 201 3.9738 0.1707
7 19.103 962 4.7074 0.9529
8 22.916 465 3.9564 1.0308
9 12.596 949 7.0643 0.65758
10 22.289 7157 4.0614 0.2154
Copyright © 2011 SciRes. MSA
Influence of Benzoate on Substituent Benzoic Acids with Implications on Spectroscopic 507
Studies through Inter Molecular Hydrogen Bonding
5. Acknowledgements
The author thanks the Management of GITAM Univer-
sity for its support in pursuing the work and especially
Dr.Trimurthulu for recording the Spectra and CIL Uni-
versity of Hyderabad in providing powdered X-ray dif-
fraction facility.
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