INTRODUCTION
Cinnamic acids and their derivatives, besides being compound of biological importance1 (they are the members of the shikimic acid metabolic pathway), offer the possibility of investigating hydrogen boning interactions as well2. The acids, among them the phenylcinnamic acids, are capable of forming hydrogen bonded network in solution through dimerization and to a smaller extent trimerization3-4. A variety of structurally different compounds have been reported to act as a aldose reductase inhibitors and contain a carboxylic acid moiety which is essential for the inhibitory effect5-6. Synthesis and activity of a series of (Z)-3-phenyl-2-benzoyl propenoic acid derivatives as aldose reductase inhibitors were reported by Wang et. al.7. Caffeic acid (trans-3-(3,4-dihydroxyphenyl)-2-propenoic acid and its ester derivatives have been synthesized recently and screened for their
Material Science Research India Vol. 5(2), 435-440 (2008)
Spectroscopic Studies and Hartree-Fock ab initio
Calculations of a 2.3-diphenylpropenoic acid ester - C
17H
16O
2C. YOHANNAN PANICKER
1*, HEMA TRESA VARGHESE
2, AL-SHIBIA S. DEEN
1,
B.HARIKUMAR
3and K. RAJU
41Department of Physics, TKM College of Arts and Science, Kollam, Kerala (India). 2Department of Physics, Fatima Mata National College, Kollam, Kerala (India). 3Department of Chemistry, TKM College of Arts and Science, Kollam, Kerala (India).
4Department of Physics, University College, Trivandrum, Kerala (India).
(Received: July 26, 2008; Accepted: August 29, 2008)
ABSTRACT
FT-IR spectra of an ester of 2,3-diphenylpropenoic acid was recorded and analyzed. The vibrational wavenumbers of the compound have been computed using the Hartree-Fock/6-31G* basis and compared with the experimental values. Predicted infrared intensities and Raman activities are reported.
Key words: Hartree-Fock ab initio calculations, FT-IR, propenoic acid.
antioxidant and anticancer activities8-14. Ferulic acid (trans-3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid) is the most abundant hydroxycinnamic acid in the plant world and has been described to be an effective antioxidant, essential for preserving the physiological integrity of cells15-17. Ab initio quantum mechanical method is at present widely used for simulating IR spectrum. Such simulations are indispensable tools to perform normal coordinate analysis so that modern vibrational spectroscopy is unimaginable without involving them. In the present study, the FT-IR and theoretical calculations of the wavenumber values of the title compound are reported.
EXPERIMENTAL
technique with 1 mg sample per 300 mg KBr was used. The title compound was prepared according to a known procedure18.
Computational details
Calculations of the title compound were carried out with Gaussian03 program19 using the HF/6-31G* basis set to predict the molecular structure and vibrational wavenumbers. Molecular geometr y was fully optimized by Ber ny’s optimization algorithm using redundant internal coordinates. Harmonic wavenumber values were calculated using the analytic second derivatives to confirm the convergence to minima on the potential surface. The wavenumber values computed at the Hartree-Fock level contain known systematic errors due to the negligence of electron correlation20. We therefore, have used the scaling factor value of 0.8929 for HF/6-31G* basis set. The absence of imaginary values of wavenumbers on the calculated vibrational spectrum confirms that the structure deduced corresponds to minimum energy. The assignment of the calculated wavenumbers is aided by the animation option of Molekel program, which gives a visual presentation of the vibrational modes21-22.
RESULTS AND DISCUSSION
The observed IR bands with the relative intensities and calculated wavenumbers and assignments are given in Table 1. The vibrations of
the CH2 group23, the asymmetric stretch νasCH 2, symmetric stretch νsCH2, scissoring vibration δCH2 and wagging vibration ωCH2, appear in the regions 2930 ± 25, 2880 ± 60, 1425 ± 20 and 1340 ± 40 cm-1. The HF calculations give νasCH
2 at 2933 and νsCH2 at 2901 cm-1. The CH
2 deformation band which comes near 1463 cm-1 in alkenes24 is lowered to about 1440 cm-1 when the CH
2 group is next to a double or triple bond. A carbonyl, nitrile or nitro group each lowers the wavenumber of the adjacent CH2 group25 to about 1425 cm-1. The band at 1417 cm-1 is assigned as the scissoring mode δCH2. The CH2 wagging mode is observed at 1332 cm-1 in the IR spectrum and at 1339 cm-1 theoretically. The band at 1275 cm-1 in IR and 1270 cm-1 HF are assigned as τCH2 which is expected in the region23 1265 ± 25 cm-1. The rocking mode ρCH
2 is expected in the region 805 ± 30 cm-1 and the band at 808 cm-1 is assigned as this mode. In the spectra of methyl esters the overlap of the regions in which both asymmetric stretching absorb with a weak to medium intensity (2985 ± 15 and 2970 ± 30 cm-1) is not large23. The HF calculations give 2992 and 2958 cm-1 as νasCH
3 modes. Experimentally only one band is observed in the IR spectrum at 2981 cm-1. The symmetric stretching mode νsCH3 is expected in the region23 2900 ± 40 cm-1 in which all three of the C-H bonds extend and contract in phase. The band at 2862 cm-1 in the IR spectrum is assigned as νsCH3 mode and the ab initio calculations give a value 2860 cm-1 for this mode. With methyl esters the overlap of the regions in which the methyl
Table 1: Calculated vibrational wavenumbers, measured Infrared band positions and assignments
υυυυυ(HF) (cm-1) υυυυυ(IR) (cm-1) IR intensity Raman activity Assignments (KM/Mol) (A**4/AMU)
3057 3057 w 4.08 61.52 υCH
3027 3033 w 14.18 336.79 υCH
3026 39.15 202.20 υCH
3017 41.21 9.98 υCH
3013 29.82 80.18 υCH
3010 25.97 66.33 υCH
3002 2.87 125.91 υCH
3000 1.40 109.30 υCH
2997 0.24 28.42 υCH
2992 1.54 26.08 υCH
2992 2981 m 2.84 21.32 υasMe
2958 45.15 9.57 υasMe
2933 2.15 90.33 υasCH2
2926 43.58 85.97 υC23-H25
2901 10.67 108.09 υsCH2
2860 2862 w 25.93 131.61 υsMe
1665 1710 vvs 141.99 435.75 υC=O
1619 1624 m 123.62 276.77 υC=C
1615 33.16 516.19 υPh
1609 137.39 118.05 υPh
1586 1589 w 3.49 8.36 υPh
1584 1580 w 11.19 59.33 υPh
1502 13.79 10.02 υPh
1502 5.43 4.43 υPh
1499 1493 m 22.28 2.11 υPh
1479 1478 w 6.27 22.34 δasMe
1466 1463 w 7.25 25.64 δasMe
1452 21.97 13.44 υPh
1447 1447 s 6.44 1.85 δPh
1417 5.07 3.49 υCH2
1400 25.86 15.68 υPh
1389 1392 w 13.56 5.82 δsMe
1345 26.56 16.40 υPh
1339 1332 w 0.31 2.97 ωCH2
1270 1275 sh 4.86 16.53 τCH2
1268 977.88 28.83 δCH
1246 1247 vvs 19.80 98.99 υC26-O27
1214 1208 s 6.73 1.44 δCH
1198 31.94 63.49 δCH
1192 11.72 16.37 δCH
1185 1176 s 1.10 7.36 δCH
1166 138.32 33.10 δCH
1163 8.21 2.59 ρMe
1147 2.24 22.90 δCH
1142 0.494 2.85 δCH
1116 11.66 11.81 ρMe
1083 1095 w 6.81 0.80 δCH
1072 1078 m 3.24 0.75 δCH
1062 1.93 6.18 δCH
1054 0.64 0.11 δCH
1035 1042 s 42.28 5.73 δC23-H25
1033 2.31 3.02 δCH
1025 1027 s 0.53 1.07 δCH
1023 4.42 5.50 δCH
1023 6.42 6.52 γCH
1018 17.57 27.84 Ring breathing
1000 1000 w 12.90 25.53 Ring breathing
994 994 w 2.41 75.49 γCH
983 6.07 20.95 γCH
970 972 w 1.46 5.14 γCH
960 0.85 5.60 υC-Me
885 890 w 0.19 3.45 γCH
883 0.43 2.52 γCH
876 873 w 11.56 18.54 γCH
827 14.70 9.48 γCH
808 7.89 2.56 ρCH2
806 24.59 5.26 γCH
792 778 s 43.27 1.01 γCH
760 5.94 12.83 δPh(X)
752 755 w 20.31 4.63 γC23-H25
721 72.52 0.71 δPh(X)
712 710 s 40.83 2.62 γPh
703 695 w 4.68 2.03 γPh
630 2.25 5.93 δPh
629 628 m 0.50 3.309 δPh
604 14.89 3.62 γPh
582 579 m 24.83 1.57 δC=O
572 4.15 12.47 γPh
492 13.25 0.20 γC=O
υ-stretching; δ-in-plane deformation; γ-out-of-plane deformation; ρ-rocking; τ-twisting; ω-wagging; s-strong; b-broad; v-very; w-weak; Me-methyl; Ph-phenyl; X-substituent sensitive; subscript : as-asymmetric; s-symmetric.
asymmetric deformation are active (1470 ± 15 and 1455 ± 15 cm-1) is quite strong, which leads to many coinciding wavenumbers. The symmetric deformation23 is expected in the range 1380 ± 15 cm-1. The calculations give 1479, 1466 cm-1 and 1389 cm-1 as asymmetric and symmetric CH
3 modes, respectively. The bands observed at 1478, 1463 cm-1 and 1392 cm-1 in the IR spectrum are assigned as these modes, respectively. The methyl
rocking modes23 are active in the region 1130 ± 60 and 1050 ± 50 cm-1. Ab initio calculations give 1163 and 1116 cm-1 as ρCH
3 modes.
are observed in the IR spectrum at 3057 and 3033 cm-1. The benzene ring possesses six ring stretching vibrations, of which the four with the highest wavenumbers (occurring respectively near 1600, 1580, 1490 and 1440 cm-1) are good group vibrations. In the absence of ring conjugation, the band near 1580 cm-1 is usually weaker than that at 1600 cm-1. The fifth r ing stretching vibration is active near 1335 ± 35 cm-1, a region which overlaps strongly with that of the CH in-plane deformation and the intensity is in general, low or medium high23,26. The sixth ring stretching vibration or ring breathing mode appears as a weak band near 1000 cm-1 in mono substituted benzenes23. The bands observed at 1589, 1580, 1493, 1447 cm-1 in the IR spectrum are assigned as νPh ring stretching modes. The ab initio calculations give these modes at 1615, 1609, 1586, 1584, 1502, 1502, 1499, 1452, 1447, 1400, 1345 cm-1. These vibrations are expected in the region23 1620-1300 cm-1. For the title c o m p o u n d t h e r i n g b r e a t h i n g m o d e s a r e assigned at 1018 and 1000 cm-1 theoretically and a weak band is observed at 1000 cm-1 in the IR spectrum. In mono substituted benzenes, CH in-plane bending vibrations of the phenyl ring are expected in the region 1000 – 1300 cm-1 and the out-of-plane γCH deformations of the phenyl ring are expected in the range23 1000 -730 cm-1. Generally, the CH out-of-plane deformations with t h e h i g h e s t wave n u m b e r s h ave a we a ke r i n t e n s i t y t h a n t h o s e a b s o r b i n g a t l owe r wavenumbers. The stronger δCH band occurring in the region 775 ± 45 cm-1 tends to shift to lower(higher) wavenumbers with increasing electron donating (attracting) power of the substituent, but seems to be more sensitive to mechanical interaction effects. The out-of-plane CH deformation at 778 cm-1 and the out-of-plane r ing defor mation γPh at 710 cm-1 in the IR s p e c t r u m fo r m a p a i r o f s t r o n g b a n d s characteristics of mono substituted benzene derivatives23,27.
The C=O stretching vibrations provides a strong absorption in the region 1740 ± 90 cm-1 for propenoic acid23. In the present case the very strong band observed at 1710 cm-1 in the IR spectrum is assigned as this C=O stretching vibration. The
deformations bands of the C=O are expected in the regions23 585 ± 115 cm-1 and 520 ±90 cm-1. The C=C stretching mode of unconjugated alkenes usually show moderate to weak absorption28 in the range 1667-1640 cm-1. For the title compound the C=C stretching mode is assigned at 1624 cm-1 in the IR spectrum and at 1619 cm-1 theoretically. For a series of propenoic acid esters Felfoldi et. al.29 reported the υC=O at 1690 cm-1 and υC=C at 1625 cm-1. For the title compound the band observed at 1247 cm-1 in the IR spectrum and at 1246 cm-1 (HF) is assigned as υC26-O27 mode. This υCO stretch is reported in the range 1240-1270 cm-1 for phenylpropenoic acid esters30.
For a phenylpropenoic acid ester, Palinko et. al.31 reported the bond lengths C
2-C23, C23-C24, C24-C26, C26-O28, C26-O27, C24-C14 as 1.475, 1.329, 1.481, 1.205, 1.362, 1.489 Å. In the present case, the corresponding lengths are 1.4730, 1.3389, 1.4859, 1.2213, 1.3402 and 1.4924 Å. In the two aromatic rings, the molecular dimensions are as expected with the aromatic C-C bond distances between 1.3850 and 1.3976 Å. The aromatic C-C-C bond angles varying from 118.3° to 121.2° are almost within the normal ranges, confirming the sp2 hybr idization of the carbon atom. However, in comparison with the normal aromatic bond values, the shorter C3-C4 (1.3856 Å) and C1-C6 (1.3850 Å) and also the smaller C1-C2-C3 bond angle of 118.3° may be attr ibuted to hyperconjugation effect32. It is of particular interest to observed that C26-O27 (1.3402 Å) is shorter than the normal C-O single bond (1.44 Å), showing the double bond feature due to conjugation effect32. Similarly, the double bond length of C
23 -C24 (1.3389 Å) is shorter than that of the typical C=C (1.3456 Å), while the C26-C24, C2-C23, C14 -C24, 1.4859, (1.4730, 1.4924 Å, respectively, shorter than the normal C-C bond length (1.54 Å) which attributes to the existence of conjugated system among ester parts and phenyl ring, also confirming the sp2 hybridization of carbon atoms32.
ACKNOWLEDGEMENTS
The authors thank Kerala State Council for Science, Technology and Environment, Government of Kerala, India, for financial support.
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