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

This study presents the comparison of conformational behaviour of two similar push–pull ethylenes in which the possibility to form an intramolecular hydrogen bond exists. The IR, Raman and NMR spectroscopic studies as well as ab initio MP2 and DFT B3LYP theoretical calculations using 6-31G** basis set confirmed that the presence of intramolecular hydrogen bond has an important influence on conformational behaviour of such type compounds. 3-methylamino-2-acetyl propenenitrile (MAAPN) H3CNHCHC(CN)(COCH3) was prepared as pure Z-isomer with intramolecular hydrogen bond while 3-methylamino-2-methylsulfonyl propenenitrile (MASPN) H3CNHCHC(CN)(SO2CH3) as pure E-isomer. MAAPN in polar solutions partially underlies to the isomerization. Such process has not been observed for MASPN which exists in solution in two conformers with the anti and syn orientation of the methylamino group towards the CC double bond, anti conformer being about 2.0 ± 0.4 kJ mol−1 more stable. The vibrational spectra of studied molecules were assigned on the base of normal coordinate calculations and potential energy distribution (PED). The use of different polarizable continuum models (IPCM, PCM) included in SCRF theory leads to controversial results in ground-state energy calculations in solutions of various polarity.