Syntheses and conformational analyses of mono- and trans-1,4-dialkoxy substituted cyclohexanes—the steric substituent/skeleton interactions

Mono- and trans-1,4-dialkoxy substituted cyclohexanes (alkyl=Me, Et, i-Pr, t-Bu) were prepared using the solvomercuration–demercuration (SM–DM) procedure. The axial⇋axial and axial,axial⇋equatorial, equatorial conformational equilibria of the products were studied by low temperature 1H and 13C NMR spectroscopy in CD2Cl2. The structures and relative energies of the participating conformers were calculated at both the B3LYP (6-311G∗//6-311+G∗) and MP2 (6-311+G∗//6-311G∗) levels of theory. In the case of DFT, good correlations of ΔGocalcd versus ΔGoexptl were obtained. Both the structures and the energy differences of the conformers have been discussed with respect to established models of conformational analysis, viz. steric and hyperconjugative interactions. In addition, 1JH,C coupling constants were considered with respect to the hyperconjugation present.