RAMAN-SPECTRA, CONFORMATIONAL STABILITY AND NORMAL-COORDINATE ANALYSIS OF ETHYLMETHYLAMINE

Raman spectra of ethylmethylamine and ethylmethylanaine-N-d, both in the liquid phase, at different temperatures, and in the solid phase were recorded. Additionally, Fourier transform IR (4000-400 cm(-1)) spectra of these compounds in the liquid phase were also obtained. Normal coordinate calculations were performed for each conformer (T, G and G'), using an optimized local symmetry force field for secondary amines. These calculations allowed the assignment of the vibrational spectra, in good agreement with the experimental evidence. Whereas in the liquid phase all the three possible conformers were detected, in the solid phase only the bands ascribed to the T conformer were observed. From the temperature dependence study of the Raman spectrum of the liquid, the enthalpy differences between conformers were determined, yielding the values 4.6 +/- 0.3 kJ nmol(-1) for Delta H-G'-T, 3.6 +/- 0.3 kJ mol(-1) for Delta H-G-T and 1.1 +/- 0.3 kJ mol(-1) for Delta H-G'-G. These were compared with ab initio SCF-MO results, for the isolated molecule, in order to assess the relative importance of intra- and intermolecular effects on conformational equilibria.