An MO-Theoretical Illumination for the Principle of Stereoselection

The principle of the stereoselection in organic chemistry has been discussed from the point of view of the molecular orbital theory. The stereoselectivity in the stereospecific ring-closure of conjugated polyenes and the stereospecific ring-cleavage of unsaturated carbon cycles, trans-1,2-noncycloadditions, cis-1,2-additions and cis-1,3-dipolar additions have been accounted for with a qualitative generalization. In many cases the symmetry relationship of certain particular molecular orbitals (“frontier orbitals”) plays a conspicuously significant role in the steric control of stereochemical processes. This may be put in contrast with the role of the frontier electron density in the orientation process in organic reactions.