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Combretastatin-A4, a potential anti-cancer drug in advanced preclinical development, is extracted from the medicinal plant Combretum caffrum. NIR-FT Raman and FT-IR spectral studies were carried out and ab initio calculations were performed at the HF/6-31G(d) level to derive equilibrium geometry and vibrational wavenumbers and intensities. The vibrational analysis shows that the molecule exhibits similar geometric behavior to cis-stilbene, and has undergone steric repulsion resulting in phenyl ring twisting with respect to the ethylenic plane. The spectral behavior of the methoxy groups is influenced by the oxygen lone pair-aryl p z orbital conjugation and back-donation. Chelation of the OH group with the oxygen lone pair of the methoxy group produces separate bands for free OH and associated OH vibrations.

Single crystals of methyl 3-(4-methoxyphenyl)prop-2-enoate were grown by the slow evaporation technique and vibrational spectral analysis was carried out using near-IR Fourier transform Raman and Fourier transform IR spectroscopy. Ab initio quantum computations were also performed at the HF/6-311G (d,p) level to derive the equilibrium geometry, vibrational wavenumbers and intensities and first hyperpolarizability. The large NLO efficiency predicted for the first time in this new class of compounds was confirmed by powder efficiency experiments. Hartree-Fock calculations reveal that the endocyclic angle at the junction of the propeonate group and the phenyl ring is decreased from 120 • by 2.5 • , whereas the two neighbouring angles around the ring are increased by 2.1 • and 1.2 • , associated with chargetransfer interaction. Vibrational analysis indicates the lowering of asymmetric stretching modes of Me1 and Me2 due to the electronic effects simultaneously caused by back-donation and induction due to the presence of the oxygen atom. The occurrence of Fermi resonance is also identified. The carbonyl stretching vibrations were lowered owing to conjugation and the hydrogen bonding network inside the crystal. The vibrational spectra confirm that the charge-transfer interaction between the -COOCH 3 group and phenyl ring through the ethylenic bridge must be responsible for simultaneous IR and Raman activation of C 7 C 18 stretching and ring modes 8 and 19. The large intensity differences observed between the 8a and 8b modes in both the IR and Raman spectra are due to the algebraic difference of the electronic effects of the substitutents. The charge transfer interaction between the -COOCH 3 group and phenyl ring through the ethylenic bridge resulting in p-electron cloud movement from donor to acceptor can make the molecule highly polarized. Intramolecular charge transfer must be responsible for the NLO activity of MMP.

Near-infrared Fourier transform Raman and

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