Abstract
Cyclohexane (1), oxygen-, sulfur-, and/or nitrogen-containing six-membered heterocycles 2−5, cyclohexanone (6), and cyclohexanone derivatives 7−16 were studied theoretically [B3LYP/6-31G(d,p) and PP/IGLO−III//B3LYP/6-31G(d,p) methods] to determine the structural (in particular C−H bond distances) and spectroscopic (specifically, one bond 1JC-H NMR coupling constants) consequences of stereoelectronic hyperconjugative effects. The results confirm the importance of nX → σ*Capp (where X = O, N), σC-Hax → π*CO, σS-C → σ*Capp, σC-S→σ*Capp, β-nO → σ*C-H, and σC-H → σ*Capp hyperconjugation, as advanced in previous theoretical models. Calculated rC-H bond lengths and 1JC-H coupling constants for C−H bonds participating in more than one hyperconjugative interaction show additivity of the effects.

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