Hyperconjugation involving strained carbon-carbon bonds. Structural analysis of ester and ether derivatives and one-bond 13C- 13C coupling constants of α- And β-nopinol

Abstract

σC-C-σ*C-O interactions involving the strained carbon-carbon bonds of α- and β-nopinol, and their ester and ether derivatives have been demonstrated in the solid state using the variable oxygen probe. These hyperconjugative interactions are manifested as a strong response of the C-OR bond distance to the electron demand of the OR substituent. Although the effects upon the donor C-C bond distances are not large enough to be measurable by X-ray crystallography, they do result in systematic and measurable effects on the 13C-13C one-bond coupling constants. For the donor C-C bond, coupling constants decrease, consistent with weakening of this bond, while the intervening C-C bond coupling constan..