Hyperconjugation as it affects conformational analysis

A primer for the qualitative identification and quantitative analysis of hyperconjugative delocalization is presented. The particular focus is upon the influence of hyperconjugation as it affects conformational analysis. Computational methodologies are illustrated within the context of several diverse molecular systems: anomeric and reverse anomeric effects in 2-tetrahydropyranosylammonium, generalized anomeric effects in phosphorus-stabilized carbanions, and hyperconjugative effects in phosphorus- and silicon-based trigonal bipyramids. Hyperconjugation is shown to compete with apicophilicity in the final examples. Although the latter influence has long been accounted for in traditional conformational analysis of trigonal bipyramidal systems, the former has been less appreciated.