Conformational isomerism and electronic interactions in some α-aminoketones

The theoretically calculated potential energy surfaces (PES), at MP2/6-31G (d,p) level of theory, for the α-aminoacetone and α-aminocyclohexanone showed the occurrence of two conformers for the former, being the synperiplanar (Sp) 3.00 kcal mol−1 much more stable than the synclinal (Sc) conformer, while three axial [two Sc and one Ap (antiperiplanar)] and one equatorial (Ap) conformers were observed for the later, with the Ap-eq as the most stable conformation (2.07 kcal mol−1 from the lower energy axial conformer). For the more complex system, the N,N-dimethyl-α-aminoacetone, a 3D potential energy surface was obtained, which led to two stable conformers (Sc-Sc and Sp-Ap; ΔESp-Ap-Sc-Sc=0.81 kcal mol−1) and two transition states (Sc-ScT and Ap-SpT), when the equivalent forms bringing an specular relationship are discarded. The stability of the different conformers for the three studied compounds were explained by the orbital interactions obtained through NBO calculations.