Directional Effects of a Conjugation on Geometrical Isomerism

The preferred geometry of many molecules can be viewed as the result of the maximization of an interaction between the best donor lone pair or bond and the best acceptor bond, i. e., the bond with the lowest lying antibonding orbital. The magnitude of this aforementioned “hyperconjugative” interaction is a function of the geometry of the interacting fragments. The anti rather than the syn orientation affords the maximal lone-pair-bond and/or bond-bond a conjugative interactions. Ab initio calculations are employed to test the model and to probe the importance of “directive” a conjugation relative to nonbonded attractive and steric effects in diverse molecular systems.