The CαC internal rotation in α‐alkyl substituted carbonyls and thiocarbonyls: CH(CH3)2C(X)YH (X, Y O or S)

Abstract The C α C internal rotation in 2‐methylpropionic, 2‐methylthiopropionic (thiol and thion forms) and 2‐methyldithiopropionic acids was studied by the ab initio SCF‐MO method using 3‐21G and 3‐21G + d (0.65S) basis sets. Energies and structures of several conformations of these molecules, determined by gradient geometry refinement, are reported and used to assess the effects of oxygen‐by‐sulphur substitution on molecular properties. The nature and relative importance of intramolecular interactions involving both the α‐methyl substituents and the C( X ) Y ( X , Y  O or S) fragment are also discussed.