Manifestations of Stereoelectronic Interactions in ~1J_(C-H) One-Bond Coupling Constants

摘要

Two-electron/two-orbital hyperconjugative interactions depend on the relative orientation of bonds and lone pairs in a molecule and are also inversely proportional to the energy difference between the interacting orbitals. Spectroscopic manifestations of stereo-electronic interactions are particularly useful experimental signatures of these effects which can be utilized for testing molecular models. Empirical observations together with theoretical interpretations in cyclohexane and six-membered heterocycles confirm the relevance of δ_(C-H_(ax)) → δ~*_(C-H_(ax)), n_x → δ~*_(C-H_(ax)) (X = O or N), δ_(C-S) → δ~*_(C-H_(eq)) , β-n_o → δ~*_(C-H_(eq)), δ_C(2)-H_(ax) → π~*_(c = y) (Y = O, S, or CH_2), and δ_(C(2)-H_(ax)) → δ~*_((S-O)_(ax)) two-electron/two-orbital stereoelectronic interactions that weaken the acceptor (or donor) C-H bonds and attenuate the Fermi contribution to the one-bond ~(13)G-~1H coupling constants.