The cornerstone of conformational analysis has been the determination and explanation of equatorial vs. axial populations of substituted (hetero)cyclohexanes. Conformational bias in these systems is usually justified by steric, polar and stereoelectronic (mostly hyperconjugative) effects. In the present talk, the conformational preferences of six-membered rings with strongly polarizing substituents, like hydroxyl and fluoride, will be analyzed by using a computational approach. Conventional justifications for the equatorial preference of cyclohexanol denote steric and hyperconjugative reasons but both models fail to clarify the conformational predisposition in a variety of substituted cyclohexanols. Using computations, we have identified attractive Coulomb interactions (ACIs) among pairs of non-bonded atoms to provide a better prediction than steric and hyperconjugative reasoning. Proper perception and implementation of ACIs leads to a dependable prognosis of conformational preferences, as demonstrated with a variety of cyclohexanol derivatives. The ACI model may be efficaciously utilized for anomeric effects as well, while for all selected cases natural bond orbital (NBO) analysis reveals a failure of hyperconjugation as an explanation for anomeric stabilization. Furthermore the case of reverse anomeric effect and conformations in dimethoxymethane can equally be competently addressed by the ACI model.

Conformational preferences and anomeric effect in light of attractive Coulomb interactions

254th National Meeting (2017)

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