Vibrational analysis and conformational study of 3-dimethylamino-2-acetyl propenenitrile and 3-dimethylamino-2-methylsulfonyl propenenitrile

The IR, Raman and NMR spectra of similar push–pull ethylenes 3-dimethylamino-2-acetyl propenenitrile (DAAPN) (H3C)2N–CHC(CN)(COCH3) and 3-dimethylamino-2-methylsulfonyl propenenitrile (DASPN) (H3C)2N–CHC(CN)(SO2CH3) were measured. According to NMR spectra both compounds were prepared as pure E-isomers. served IR and Raman bands were compared with harmonic vibrational frequencies, calculated using ab initio MP2 and B3LYP density functional methods in 6-31G** basis set, and assigned on the base of potential energy distribution. In addition, the geometries and relative energies of possible conformers and isomers of the studied compounds were also evaluated on the same levels. ional spectra revealed that in polar solutions E-DAAPN exists as two conformers with Z or E orientation of acetyl group, the Z conformer being about 2.2±0.3 kJ mol−1 more stable than the E one. The influence of environment polarity on this conformational equilibrium is discussed with respect to the SCRF solvent effect calculations using IPCM and PCM models.