The molecular structure and vibrational spectra of methyl 3-(amino)-2-butenoate (MAB) and its deuterated analogous, D3MAB, were investigated using density functional theory (DFT) calculations. The geometrical parameters and harmonic vibrational wavenumbers of MAB and D3MAB were obtained at the B3LYP/6-311++G(d,p) level. The calculated vibrational wavenumbers were compared with the corresponding experimental results. The assignment of the IR and Raman spectra of MAB and D3MAB was facilitated by calculating the anharmonic wavenumbers at the B3LYP/6-311G(d,p) level as well as recording and calculating the MAB spectra in CCl4 solution. The assigned normal modes were compared with a similar molecule, 4-amino-3-penten-2-one (APO). The theoretical results were in good agreement with the experimental data. All theoretical and experimental results indicate that substitution of a methyl group with a methoxy group considerably weakens the intramolecular hydrogen bond and reduces the π-electron delocalization in the chelated ring system. The IR spectra also indicate that in the solid state, MAB is not only engaged in an intramolecular hydrogen bond, but also forms an intermolecular hydrogen bond. However, the intermolecular hydrogen bond will be removed in dilute CCl4 solution.

Keywords