Solution-Phase Conformations of N-Acetyl-N‘-methyl- l -alaninamide from Vibrational Raman Optical Activity

Experimental and ab initio theoretical vibrational Raman optical activity (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, CHCl 3, H 2 O, and D 2 O. The ab initio VROA spectra were predicted for nine different conformations of NANMLA optimized with the 6-31G* basis set. The vibrational frequencies and normal modes for all nine conformers were also obtained with the 6-31G* basis set. From a comparision of the predicted and observed VROA spectral patterns, it is suggested that there is reasonable support for the presence of C 7,eq −C 5, C 7,eq, and α R conformers in aqueous solution and for C 7,eq −C 5 and α R conformers in chloroform solutions.