SOLUTION-PHASE CONFORMATIONS OF N-ACETYL-N'-METHYL-L-ALANINAMIDE FROMVIBRATIONAL RAMAN OPTICAL-ACTIVITY

Experimental and ab initio theoretical vibrational Raman optical activ ity (VROA) spectra are presented for N-acetyl-N'-methyl-L-alaninamide (NANMLA), in order to determine the predominant conformations of this molecule in the solution phase. The experimental spectra were obtained in three different solvents, CHCl3, H2O, and D2O. The ab initio VROA spectra were predicted for nine different conformations of NANMLA opti mized with the 6-31G basis set. The vibrational frequencies and norma l modes for all nine conformers were also obtained with the 6-31G bas is set. From a comparision of the predicted and observed VROA spectral patterns, it is suggested that there is reasonable support for the pr esence of C-7,C-eq-C-5, C-7,C-eq, and alpha(R) conformers in aqueous s olution and for C-7,C-eq-C-5 and alpha(R) conformers in chloroform sol utions.