Synthesis and characterization of cinnamylidene acetone – A study on tuning of band gap by vibrational spectroscopic tools

Article abstract of DOI:10.1016/j.molstruc.2019.02.057

The title molecule Cinnamylidene acetone (CA) was synthesized through a single step base catalyzed aldol type condensation between acetone and cinnamaldehyde. The prepared molecule has been characterized using NMR (¹H and ¹³C) spectral analysis, FTIR, UV–Vis and Elemental analysis. The complete vibrational characterization of the molecule was performed using experimental (FTIR and FT-Raman) spectra and calculations at DFT level. In order to carry out a detailed vibrational spectroscopic analysis of CA, Fourier Transform Infrared and Fourier Transform Raman spectra recorded in condensed phase were used. To determine the optimized geometry and vibrational wavenumbers, Density functional theory calculations in the B3LYP/6-31G** level have been carried out followed by scaling using the scaled quantum mechanical methodology. A root mean square deviation of 6.53 cm^?1 has resulted from the scaled quantum mechanical treatment. The ultraviolet visible spectra of the title compound dissolved in various solvents were recorded in the range of 300–600 nm. The natural bond orbital and frontier molecular orbital analyses were also performed using B3LYP/6-31G** method. These studies revealed a reduction in the band gap of CA in comparison with that of cinnamaldehyde (CY).

Full text of DOI:10.1016/j.molstruc.2019.02.057

Accepted Manuscript
Synthesis and characterization of cinnamylidene acetone – A study on tuning of band
gap by vibrational spectroscopic tools
V. Ragavendran, S. Muthunatesan, V. Santhanam, Biljana Arsic
PII:
S0022-2860(19)30188-7
DOI:
https://doi.org/10.1016/j.molstruc.2019.02.057
MOLSTR 26214
Reference:
To appear in: Journal of Molecular Structure
Received Date: 1 November 2018
Revised Date: 13 February 2019
Accepted Date: 14 February 2019
Please cite this article as: V. Ragavendran, S. Muthunatesan, V. Santhanam, B. Arsic, Synthesis and
characterization of cinnamylidene acetone – A study on tuning of band gap by vibrational spectroscopic
tools, Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.02.057.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Synthesis and characterization of cinnamylidene acetone – A study on tuning of band gap
by vibrational spectroscopic tools
a
b
c
d
V Ragavendran *, S Muthunatesan , V Santhanam and Biljana Arsic
a
Department of Physics, Sri Chandrasekharendra Saraswathi Viswa Mahavidyalaya, Kanchipuram - 631561, Tamilnadu, India
b
Department of Physics, Government Arts College (Autonomous), Kumbakonam - 612001, Tamilnadu, India
c
Department of Chemistry, Sri Chandrasekharendra Saraswathi Viswa Mahavidyalaya, Kanchipuram - 631561, Tamilnadu, India
d
Department of Mathematics, University of NIS, Visegradska-33, 18000, Nis, Republic of Serbia
Abstract
The title molecule Cinnamylidene acetone (CA) was synthesized through a single step
base catalyzed aldol type condensation between acetone and cinnamaldehyde. The prepared
1
13
molecule has been characterized using NMR ( H and C) spectral analysis, FTIR, UV-Vis and
Elemental analysis. The complete vibrational characterization of the molecule was performed
using experimental (FTIR and FT-Raman) spectra and calculations at DFT level. In order to
carry out a detailed vibrational spectroscopic analysis of CA, Fourier Transform Infrared and
Fourier Transform Raman spectra recorded in condensed phase were used. To determine the
optimized geometry and vibrational wavenumbers, Density functional theory calculations in the
B3LYP/6-31G** level have been carried out followed by scaling using the scaled quantum
-1
mechanical methodology. A root mean square deviation of 6.53 cm has resulted from the scaled
quantum mechanical treatment. The ultraviolet visible spectra of the title compound dissolved in
various solvents were recorded in the range of 300-600 nm. The natural bond orbital and frontier
molecular orbital analyses were also performed using B3LYP/6-31G** method. These studies
revealed a reduction in the band gap of CA in comparison with that of cinnamaldehyde (CY).
Keywords: Synthesis, DFT, SQM, Extended conjugation, Band gap tuning.
Corresponding Author
*
V.Ragavendran. E-mail: ragav910@gmail.com. Phone: +91 9994015808.
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1
. Introduction
Cinnamaldehyde is one of the phytochemicals found in cinnamon and exhibits several
biological effects such as anti-tumoural, anti-oxidative, anti-hyperglycemic, anti-obesity and
anti-inflammatory activities to relieve heart injury in metabolic syndrome [1-4]. Earlier, the
effects of cinnamaldehyde as an antimicrobial agent have been described [5-7]. Cinnamaldehyde
is a good food preserving agent and also used to enhance flavour and odour. It was used as
decorative cosmetics worldwide in the range 100–1000 metric tonnes per annum [8]. Reports
show that it inhibits the growth of Staphylococcus aureus [5], Salmonella enterica serovar
Typhimurium [6], Clostridium botulinum [9] and Escherichia coli O157:H7. The blockage of
CD36-mediated TLR4/6-IRAK4/1 signaling to suppress NLRP3 inflammasome activation by
cinnamaldehyde and allopurinol was studied earlier [10]. Its inhibition property towards
cyclooxygenase (COX)-2 activity with IC value of 245 ꢀM in vitro was previously studied [7].
5
0
Through activation of the mitogen-activated protein kinases (MAPK) pathway and proapoptotic
Bcl-2 family proteins, cinnamaldehydes were found to be effective in inducing apoptotic cell
death in a number of human cancer cells [11-14]. Cinnamaldehyde is also well-known as the
principal agonist of transient receptor potential-ankyrin receptor 1 which is responsible for
diverse sensory processes including cold and warm nociception, hearing or inflammatory pain.
Cinnamon extract has been linked to many different health benefits like against obesity and
diabetic conditions [15-20]. Besides these, hydrogenation of cinnamaldehyde, organocatalytic
reaction mechanism, its role as a catalyst, metal support interactions and solvent effects were
studied earlier [21-26]. Beyond the taste impact of spices, numerous health benefits have been
ascribed to naturally derived flavouring molecules and are known for their use in traditional
medicine and positive effects on human health. Many reports were made with the aid of electron
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diffraction and microwave spectroscopy in the structure determination of trans-cinnamaldehyde
[27,28]. However, the molecular mechanisms by which these derivatives mediate their effects
remain largely unknown and their vibrational picture has not yet been elucidated.
In molecular systems like cinnamaldehyde, as conjugation increases there will be a
decrease in HOMO-LUMO energy gap and the position of π - π* absorption will shift to longer
wavelength [29]. More the conjugation, longer the absorption maximum. Also, the trans isomer
absorbs at a longer wavelength and with a larger molar extinction than cis conformer [29]. This
phenomenon has motivated us to take up the present study in which we have investigated the
effect of conjugation extension on the band gap, utilizing tools like UV, NBO and HOMO-
LUMO analyses, when cinnamylidene acetone is formed from cinnamaldehyde. In the present
study, (3E,5E)-6-phenyl-3,5-hexadien-2-one, also known as Cinnamylidene acetone (CA), was
synthesized taking Cinnamaldehyde (CY) as the base compound and was characterized using
NMR, FTIR, UV-VIS, and Elemental analyses. The synthesized compound is further used:
(i) To identify the most stable form of the title compound among the different
conformers,
(ii) To investigate its complete vibrational behavior using Fourier Transform Infrared
(
FTIR), Fourier Transform Raman (FT-Raman) spectra along with Density Functional Theory
DFT) level calculations.
(
Further, the crystallographic structure data of cinnamaldehyde were obtained from
literature [30] and the same was used for performing DFT calculations to obtain band gap and
UV-Vis absorption spectra of cinnamaldehyde. The results thus obtained were compared with
that of cinnamylidene acetone.
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2
. Methods
2
.1. Synthesis details
Cinnamylidene acetone was prepared through a single step base catalyzed aldol type
condensation between acetone and cinnamaldehyde which were taken in 1:1 mole ratio. The
reaction mechanism is as shown in the Fig. 1 and the procedure is very well illustrated in Fig. 2.
All starting materials, cinnamaldehyde, NaOH (SD Fine Chemicals, India) and acetone (CDH,
India) were purchased of high purity and used as received without further purification.
The position of Figure 1
In a clean 25 ml beaker, 4 ml of ethanol was taken and cinnamaldehyde (2.0 mmol,
0
.2643 g) was added followed by acetone (2.0 mmol, 0.1161 g) under magnetic stirring. With
continuous stirring, 4 ml of 3M NaOH was added in drops. After about 45 s, a yellow precipitate
of Cinnamylidene acetone was formed. The stirring was continued for another 20 min to ensure
the completion of the reaction. A mixture of ethanol and water in 1:2 ratio (10 ml) was prepared
and half of the mixture was added and stirred well; after another 20 min remaining aqueous
alcohol was added. The reaction mixture was filtered under vacuum and the yellow solid was
washed with cold aqueous ethanol. The precipitate was dried and recrystallized twice from
boiling ethanol. The yield was found to be 63% (0.2169 g). The product was characterized by the
1
13
spectral methods including FTIR, UV-Vis and NMR ( H and C), and its composition
confirmed using elemental analysis.
The position of Figure 2
2
.2. Experimental details
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The FTIR spectrum of CA was recorded for the KBr disks prepared using Perkin–Elmer
spectrum RX1 spectrophotometer equipped with Helium–Neon laser source, potassium bromide
-1
-1
(
KBr) beam splitter and LiTaO detector in the region 4000–400 cm with a resolution of 1 cm .
3
The FT-Raman measurements for CA was made using the Nicolet model 950 FT-Raman
spectrometer using 1064 nm line of a Nd:YAG laser for excitation at a 200 mW output power in
-1
-1
the range 4000-50 cm with a resolution of 4 cm .
The UV-Vis absorption spectrum of the title compound was recorded in the range 600-
-1
3
00 cm using Analytik Jena Specord 200 Plus UV-Visible spectrophotometer (Germany). The
1
13
H (400 MHz; CDCl ) and C (400 MHz; CDCl ) Nuclear Magnetic Resonance (NMR) spectra
3
3
were recorded on a Bruker HC400 instrument. Reports on chemical shifts for protons are made
in parts per million scales (δ scale) downfield from tetramethylsilane.
CHO elemental composition of CA was determined using LECO TruSpec Micro
Analyser, and determination was done twice.
2
.3. Computational details
The Gaussian 09 Program suite [31] was utilized to perform Quantum chemical
calculations on CA by applying DFT method at the B3LYP level [32,33] using 6-31G** basis
set. The stable conformer of CA was identified from the energy optimization at the DFT level of
theory. During the optimization procedure, all the geometrical parameters were allowed to relax.
Further, in order to express the normal modes in a molecular fixed coordinate system, a set of
local symmetry coordinates was defined as recommended by Pulay et al. [34] and are listed in
Table S1. The Molvib 7.0 program written by Tom Sundius [35] was utilized to perform full
normal coordinate analysis (NCA) on cinnamylidene acetone. The force fields were first
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transformed from Cartesian to local symmetry coordinates and scaled using selective scale
factors as recommended by Pulay et. al [34-37] followed by the subsequent normal coordinate
analysis which includes the refinement of the scale factors by the least square fit, potential
energy distribution (PED) calculation and prediction of IR and Raman intensities.
3
. Results and discussion
3
.1. Investigation of conformational stability through DFT analysis
The initial assumption was that the title compound may exist in different conformations.
Based on this, seven different possible conformers were chosen for CA. The seven conformers
were given names as conformer 1, conformer 2, conformer 3, conformer 4, conformer 5,
conformer 6 and conformer 7 and their structures were given in Figure 3(A) – 3(G). To obtain
the most stable geometry, structure optimization was performed on all the seven conformers
using the DFT/B3LYP method at 6-31G** level. The optimized energies of all the conformers
were tabulated as shown in Table 1. Of the seven different energy conformers, the conformer 5
(Table 1, Figure 3(E)) was found to have the lowest energy and thus it was identified as the most
stable conformer. Hence, conformer 5 was chosen for further investigation.
The position of Figure 3
The position of Table 1
3
.2. Molecular geometry
The most stable conformer (conformer 5) was obtained when the dienyl moiety settles
into all trans form (Table 1, Figure 3(E)). The global minimum energy of the most stable
conformer (conformer 5) obtained from DFT structure optimization was found to be
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-539.72465824 Kcal/mol. The optimized geometrical parameters of the most stable conformer of
CA were shown in Table 2.
The position of Table 2
3
.3. NMR analysis
The structure of synthesized CA molecule was confirmed by using H and C NMR
1
13
1
13
spectra. The experimental chemical shifts in H and C NMR spectra of (3E, 5E)-6-phenyl-3,5-
hexadien-2-one (CA) were compared with the theoretically predicted chemical shifts obtained
1
using website www.nmrdb.org [38-43]. The values are tabulated in Table 3 [ H shifts] and Table
1
3
4
[ C shifts].
The position of Figure 4(A) and Figure 4(B)
1
13
The H and C spectra of CA were shown in Figures 4(A) and 4(B), respectively. The total
number of signals in the spectra does not get correlated with the number of types of protons due
to the overlapping of the peaks of aromatic protons 6-10, in the region of 7.25–7.36 ppm. The
terminal methyl protons are appearing as singlet as expected in the moderately deshielded region,
due to the electron withdrawing nature of carbonyl group. The four alkenyl protons 2, 3, 4 and 5
appear in the deshielded region because of the anisotropy of the ethylenic systems. Since there
are considerable amounts of overlaps, calculation of coupling constants at this resolution level
becomes impossible.
The position of Table 3 and Table 4
3
.4. Elemental analysis
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Elemental analysis shows 83.30 % C, 7.00 % H, and 9.30 % O, which is the good
agreement with the calculated values (83.69% C, 7.02 % H, and 9.29 % O). These data together
with IR, UV-VIS and NMR data confirmed the structure of cinnamylidene acetone as the
synthesized compound.
3
.5. Molecular vibrations and simulated spectra
The title compound CA belongs to C point symmetry and its 69 fundamentals are
S
distributed among the symmetry species as:
Γvib = 47A′(in–plane) + 22A″(out– of–plane)
The combined observed and calculated FT–IR and FT–Raman spectra of CA were
presented in Figure 5 and Figure 6, respectively. For the title compound CA, the results of
vibrational analysis viz., calculated unscaled and scaled SQM wavenumbers, potential energy
distributions (PED) and assignment of the fundamentals, were collected in Table 5.
The position of Table 5
3
.6. Analysis of vibrational spectra by SQM methodology and assignments
Generally, the unscaled B3LYP/6–31G** vibrational wavenumbers are somewhat larger
than the observed values and is reflected in the values depicted in Table 5. The RMS deviation of
-1
6
0.1 cm was observed between unscaled and experimental wavenumber of CA. However, using
a set of transferable scale factors recommended by Rauhut and Pulay [44,45], the force fields
were scaled in order to obtain reliable information of the vibrational properties.
The calculated wavenumbers were subjected to three types of scaling procedures namely,
unscaled, uniform scaling and selective scaling. In uniform scaling, an RMS deviation of 23.4
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-1
cm was obtained by applying a scale factor of 0.99 uniformly to all unscaled wavenumbers.
Further, in order to refine the calculated wavenumbers, selective scaling using scale factors 0.99,
1
.05, 0.95, 0.922 and 0.85 was done. The selective scaling procedure results in the RMS
-1
deviation of 6.53 cm (Refer Table S1).
The position of Figure 5 and Figure 6
3
.6.1. Ring vibrations
C–H vibrations
The aromatic compounds exhibit C–H stretching vibrations generally in the region 3105–
-1
3
000 cm [46-48]. This vibration in CA was observed in the IR spectrum at 3098, 3080, 3075,
-1
-1
and 3056 cm and in the Raman spectrum at 3084 and 3059 cm .
-1
In general, the weak bands observed in the region 1250-990 cm correspond to C–H in-
plane bending vibrations [49]. For CA, these bands are observed at 1232, 1183, 1155 and 1068
-1
-1
cm in the IR spectrum and in the Raman spectrum at 1244, 1213, 1161 and 980 cm . The C–H
out–of–plane bending mode of the title compound was observed in the IR spectrum at 890, 848,
-1
-1
7
50 and 692 cm and in the Raman spectrum at 876, 779 and 689 cm , respectively and are
presented in Table 5.
Skeletal vibrations
-1
The C=C stretching vibrations generally occur in the region 1625-1430 cm [46-52]. The
-1
IR bands observed at 1600 and 1494 cm were assigned to C=C stretching vibrations of CA and
-1
their Raman counterparts were identified at 1566, 1491 and 1472 cm . In CA, the C–C
-1
stretching vibration was observed at 1316 and 1232 cm as IR bands and as Raman bands at
-1
1
315 and 1213 cm respectively.
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The aromatic ring in-plane and out-of-plane deformation vibrations were observed in the
-1
-1
-1
region 630-605 cm and 560-415 cm , respectively. The IR band observed at 627 cm and the
-1
Raman bands observed at 661 and 627 cm were attributed to the ring in-plane bending
-1
vibrations. For CA, the bands due to ring torsion vibrations were observed at 503 cm in IR
-1
spectrum and their Raman counterparts were identified at 536 and 401 cm .
3
.6.2. Alkene vibrations
C–H vibrations
The trans C–H stretching vibrations are generally observed as medium to strong bands in the
-1
region 3040–3010 cm [46-48]. This vibration of CA is observed as strong band in the IR
-1
-1
spectrum at 3024 cm . In the Raman spectrum of CA it was observed at 3036 and 3020 cm .
In general, the C–H in-plane bending vibrations were observed as several bands with weak to
-1
-1
-1
medium intensity in the regions 1340-1260 cm , 1305-1215 cm and 1000-910 cm
-1
respectively [49]. For CA, these bands are observed at 1316 and 1274 cm in the IR spectrum
-1
and in the Raman spectrum at 1385, 1335, 1315 and 1296 cm . For dienes, the C–H out–of–
-1
.
plane bending modes were generally observed in the region 980-955 cm In particular for trans-
-1
trans system, the presence of conjugation increases frequency and it may be around 1000 cm .
The C–H out–of–plane bending modes of the title compound are observed in the IR spectrum at
-1
-1
9
26 cm and in the Raman spectrum at 999 and 926 cm , respectively and are presented in
Table 5.
C–C vibrations
The alkene C=C stretching vibrations are generally observed in the region 1670-1610
-1
-1
cm as medium to weak IR band and strong Raman band, and at 1610-1580 cm as medium IR
1
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band and medium to weak Raman band [46-52]. For conjugated dienes, two absorption bands
-1
-1
occur generally at 1650 and 1600 cm . The presence of 1600 cm confirms the presence of
conjugation. In cases similar to title compound, alkenes conjugated to aromatic rings exhibit
-1
-1
strong absorption near 1625 cm which shifts the ring C=C absorption to 1590 cm . The IR
-1
band observed at 1568 cm was assigned to C=C stretching vibrations of CA and their Raman
-1
counterpart was identified at 1607 cm .
-1
The Raman bands observed at 1152 and 1094 cm were attributed to the C=C in-plane
bending vibrations. Their IR counterparts could not be observed. For CA, the bands due to C=C
-1
out-of-plane vibrations were observed as Raman bands at 554, 316, 162, 85, 64 and 37 cm .
.6.3. C=O vibrations
Generally, the C=O stretching vibration occurs in the region 1730-1450 cm [50-52]. The
3
-1
-1
band identified at 1657 cm in the IR and Raman spectrum indicates the presence of C=O
stretching vibrations of CA. The C=O in-plane bending vibrations were observed as Raman band
-1
-1
at 1177 cm and the vibration observed at 427 cm contributes to the C=O out-of-plane bending
vibrations of CA.
3
.6.4. Methyl group vibrations
The nine fundamental vibrations of methyl group were classified into ν + 2ν + 2 δ + δ
s
s
as
as
+
2ω + τ [46]. The methyl asymmetric stretching vibrations are generally expected in the region
-1
-1
-1
3
045-2965 cm and 3010-2960 cm [46-55]. The IR band identified at 3000 cm and the Raman
-1
bands at 3000 and 2966 cm confirms the presence of CH
3
asymmetric vibrations. The methyl
-1
symmetric stretching vibrations were usually expected in the region 2970-2840 cm [46-55].
1
1

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-1
-1
The weak bands identified at 2852 cm and 2851 cm in the IR and Raman spectra correspond to
methyl symmetric stretching vibrations.
The asymmetric methyl deformation vibrations were observed in the region 1465-1415
-1
-1
cm and 1440-1410 cm and the methyl symmetric deformation vibrations were expected in the
-1
-1
region 1390-1340 cm . For the title compound, the bands observed at 1445 and 1406 cm in the
FT-IR and Raman spectra indicates the presence of methyl asymmetric deformation vibrations.
-1
-1
The IR band observed at 1353 cm and the Raman band at 1356 cm confirms the presence of
methyl symmetric deformation vibrations.
The methyl out-of-plane rocking vibrations were generally observed in the region 1155-
-
1
-1
1
9
015 cm and 1070-900 cm . For the title compound, a shoulder observed in the IR spectrum at
-
1
-1
51 cm and the weak bands observed in the Raman spectrum at 1030 and 957 cm correspond
to methyl out-of-plane rocking vibrations. The methyl torsional vibrations were generally
-1
expected in the region 270-130 cm . This vibration for the title compound was identified as a
-1
weak Raman band at 239 cm .
4
. Frontier molecular orbital analysis
The HOMO, LUMO energies and the energy gap for CA and cinnamaldehyde [30] were
calculated using B3LYP/6-31G** method [56,57] and the values thus obtained were properly
tabulated as shown in Table 6. Their graphical illustration was presented in Figure 7. For CA, a
total number of 46 occupied orbitals and 209 virtual orbitals were observed.
The position of Table 6
The analysis indicates that, the frontier molecular orbitals of CA are mainly composed of
p type–atomic orbitals. The HOMO was observed over the entire molecule except that of methyl
1
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group whereas the LUMO spreads throughout the molecule. The calculations show that the band
gap was found to be 3.801 eV and 4.614 eV for CA and cinnamaldehyde, respectively. From the
results obtained, it was clear that the band gap has been reduced when cinnamaldehyde becomes
CA. This tuning effect in the band gap is because of the extended conjugation observed in CA.
The position of Figure 7
5
. Ultraviolet – Visible spectral analysis
The UV-Vis spectra of CA were recorded using ethanol, dimethyl formamide (DMF) and
ethyl acetate and are presented in Figure 8. The theoretical electronic excitation of CA obtained
by TD-DFT calculations using B3LYP/6-31G** method on the optimized structure of CA [58]
along with their corresponding wavelengths and assignments were presented in Table 7. The
experimental excitations were observed at 374, 368 and 363 nm for ethanol, DMF and ethyl
acetate, respectively. Their calculated counterparts were observed at 362, 361 and 366 nm.
Further, the crystallographic data of cinnamaldehyde (CY) thus obtained from literature [30] was
used to calculate the electronic absorption spectra. The calculated gas phase absorption was
observed at 278 nm and 382 nm for cinnamaldehyde and CA, respectively. The absorption
wavelength was found to be increased in cinnamylidene acetone as compared to
cinnamaldehyde. This increase in absorption wavelength of CA implies that its band gap is
reduced as compared to that of CY. This result further confirms our observations made in the
Frontier molecular orbital analysis.
The position of Table 7
The position of Figure 8
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6
. Natural bond orbital analysis
The Natural Bond Orbital (NBO) analysis for the title compound using NBO 5.1 program
59] as implemented in the Gaussian 09W package at the DFT/B3LYP/6-31G** level was
[
carried out. The donor–acceptor interactions involving electron density (ED) changes for the title
compound were calculated employing second order perturbation theory [60-63].
The position of Table 8
For the title compound, the most predominant electron donor-acceptor interactions were
presented in Table 8. The energy transfer mechanism from the bond pairs (π) of the ring atoms to
its antibonding (π*) orbitals and from the lone pair (LP) of oxygen atom (O ) into the bond pairs
2
1
was found to be predominant. In particular, for the transition from the lone pairs of oxygen (O )
2
1
(
2)
atom into the bond pairs, larger E values of 19.56 and 20.45 Kcal/mol were observed.
In addition, strong hyperconjugative interactions for the transition from bond pair (π) of the
ring atoms to its antibonding (π*) orbitals with greater energy contributions of 18.87, 20.17,
1
6.38, 19.05, 19.83, 20.70 and 19.37 Kcal/mol were observed.
. Conclusion
7
The title molecule Cinnamylidene acetone was synthesized through a single step base
catalyzed aldol type condensation between acetone and cinnamaldehyde. The prepared molecule
1
13
has been characterized using H and C NMR, FTIR, UV-Vis spectral analyses and elemental
analysis. The complete vibrational characterization of the molecule was done by using
experimental (FTIR and FT-Raman) spectra and calculations at DFT level. From the structure
optimization, the most stable conformer of CA was identified using DFT/B3LYP/6-31G**
methodology.
1
4

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By adopting selective scaling procedure, a satisfactory assignment of most of the
fundamentals was made. The results from the HOMO-LUMO analysis establish that CA and
cinnamaldehyde possess energy gap of 3.801 eV and 4.614 eV, respectively. This result
establishes that the band gap has been reduced when cinnamaldehyde becomes CA. The reason
for this tuning effect in band gap is due to the extended conjugation observed in CA. The
calculated comparative UV-Vis analysis result confirms the reduction in band gap of
cinnamylidene acetone when compared to cinnamaldehyde. The results from NBO analysis
establish that the stabilization of CA seems to be highly dependent on the charge transfer from
bond pairs (π) of the ring atoms to its antibonding (π*) orbitals and from the lone pair (LP) of
oxygen atom (O ) into the bond pairs.
2
1
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
The authors are thankful to Sophisticated Analytical Instrumentation Facility (SAIF) - IIT
Madras, IIT Ropar and Department of Optoelectronics, University of Kerala for providing
spectral measurements.
Funding
Dr Biljana Arsic wants to thank the Ministry of Science, Education and Technological
Development of Republic of Serbia for the financial support for this work [Proj. No 174007].
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Figure Captions
Fig. 1 Reaction mechanism of the synthesis of Cinnamylidene acetone.
Fig. 2 Graphical representation of preparation process of Cinnamylidene acetone
Fig. 3 Different conformers of Cinnamylidene acetone
1
Fig. 4(A) H spectrum of (3E, 5E)-6-phenyl-3,5-hexadien-2-one
1
3
Fig. 4(B) C spectrum of (3E, 5E)-6-phenyl-3,5-hexadien-2-one
Fig. 5 Combined FT-IR spectra of Cinnamylidene acetone
(
A) Observed, (B) Calculated – Selective scaling, (C) Calculated – Uniform scaling and
D) Calculated - Unscaled
(
Fig. 6 Combined FT-Raman spectra of Cinnamylidene acetone
(
A) Observed, (B) Calculated – Selective scaling, (C) Calculated – Uniform scaling and
D) Calculated - Unscaled
(
Fig. 7 Comparative HOMO and LUMO plot of cinnamaldehyde with cinnamylidene acetone
Fig. 8 Ultraviolet-Visible absorption spectra of CA
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Table Captions:
Table 1. Different conformers of Cinnamylidene acetone with their optimized energies
Table 2. Optimized geometrical parameters of most stable conformer of CA obtained by
B3LYP/6–31G** density functional calculations
1
Table 3. Comparison of predicted and experimental H NMR shifts of (3E, 5E)-6-phenyl-3,5-
hexadien-2-one
13
Table 4. Comparison of predicted and experimental C NMR shifts of (3E, 5E)-6-phenyl-3,5-
hexadien-2-one
-1
Table 5. Calculated wavenumbers (cm ) of Cinnamylidene acetone by B3LYP/6–31G**
method and vibrational assignments based on potential energy distribution
Table 6. Comparison of HOMO, LUMO energies of CA and Cinnamaldehyde (CY) along with
their energy gap
Table 7. Electronic absorption spectra of CA along with their excitation and assignments
Table 8. Second order perturbation theory analysis by Fock matrix of CA using Natural Bond
Order analysis
2
5

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Supplementary information (Table):
Table S1. Definition of local symmetry coordinates used in B3LYP/6–31G** force fields for
Cinnamylidene acetone.
2
6

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Table 1. Different conformers of Cinnamylidene acetone with their optimized energies
Optimized energy
Conformers
(
Kcal/mol)
Conformer 1
Conformer 2
Conformer 3
Conformer 4
-539.72465815
-539.72302573
-539.71855398
-539.71855468
-539.72465824
-539.71713454
-539.71713452
*
Conformer 5
Conformer 6
Conformer 7
*- Most stable conformer of CA

ACCEPTED MANUSCRIPT
Table 2. Optimized geometrical parameters of most stable conformer of CA obtained by B3LYP/6–31G** density
functional calculations
Bond length Value (Å)
Bond angle Value (°)
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C1–H7
C6–H8
C5–H9
C4–H10
C3–H11
C2–C12
C12–H13
C12–C14
C14–H15
C14–C16
C16–H17
C16–C18
C18–H19
C18–C20
C20–O21
C20–C22
C22–H23
C22–H24
C22–H25
1.408
1.409
1.390
1.399
1.395
1.087
1.086
1.086
1.086
1.085
1.461
1.089
1.354
1.089
1.439
1.089
1.352
1.088
1.481
1.225
1.519
1.097
1.097
1.090
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C1
C6–C1–C2
H7–C1–C2
H7–C1–C6
H8–C6–C1
117.99
120.80
120.41
119.59
120.02
121.19
119.01
119.79
119.81
120.17
120.25
120.15
119.95
119.64
119.28
119.92
114.94
127.86
120.39
122.65
117.92
125.21
120.64
121.22
H8–C6–C5
H9–C5–C6
H9–C5–C4
H10–C4–C5
H10–C4–C3
H11–C3–C4
H11–C3–C2
C2–C12–H13
C2–C12–C14
C12–C14–H15
C12–C14–C16
C14–C16–H17
C14–C16–C18
C16–C18–H19
C16–C18–C20
C18–C20–O21
C18–C20–C22
C20–C22–H23
C20–C22–H24
C20–C22–H25
122.19
116.51
110.47
110.47
109.73