C-13-C-13 spin-spin coupling constants in structural studies: XXVII. Stereospecificity of C-13-C-13 spin-spin coupling constants in heteroatomic compounds with free internal rotation about the C-X bond (X = O, S, N, P)

Quantum-chemical study of heteroatomic compounds with free internal rotatio n about the C-X bond (X = O, S, N, P) showed that the observed stereospecif icity of C-13-C-13 spin-spin coupling constants is the result of joint acti on of two competing factors: intramolecular steric interactions which lead to change of the bond angles and s-orders of bonds and effect of the unshar ed electron pairs on the heteroatom, whose contribution to the C-13-C-13 co upling constant is determined by mutual orientation of the unshared electro n pair orbital and the corresponding carbon-carbon bond.