Conformational, structural, vibrational, electronic and quantum chemical investigations of cis-2-methoxycinnamic acid

•Spectral properties of cis-2-methoxycinnamic acid have been studied.•The more stable conformations of the molecule are determined.•The stable structure has CO and CC bond in s-cis orientation.•The barrier height between more and less stable conformer is 2.43 kcal mol−1.•The MEP has the range +1.140e × 10−2 to −1.140e × 10−2.

The Fourier transform infrared (FTIR) and FT-Raman spectra of cis-2-methoxycinnamic acid have been measured in the range 4000–400 and 4000–100 cm−1, respectively. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman data. The geometry was optimised without any symmetry constrains using the DFT/B3LYP method utilising 6-311++G∗∗ and cc-pVTZ basis sets. The thermodynamic stability and chemical reactivity descriptors of the molecule have been determined. The exact environment of C and H of the molecule has been analysed by NMR spectroscopies through 1H and 13C NMR chemical shifts of the molecule. The energies of the frontier molecular orbitals have also been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. The vibrational frequencies which were determined experimentally are compared with those obtained theoretically from density functional theory (DFT) gradient calculations employing the B3LYP/6-311++G∗∗ and cc-pVTZ methods.

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