A MOLECULAR-ORBITAL AND CRYSTALLOGRAPHIC STUDY OF THE STRUCTURE AND PI-FACIAL REGIOSELECTIVITY OF 9-CHLORO-1,4,5,8-TETRAHYDRO-4A,8A-METHANONAPHTHALENE

The title compound 1 undergoes reaction with electrophilic reagents such as dichlorocarbene regioselectively on the pi-face endo to the chlorine. The crystal structure of 1 indicates significant geometrical distortions of the two rings, which we attribute to a stabilising interaction between the C-Cl sigma* orbital and the exo pi-orbital. PM3 calculations of these orbitals, the electrostatic potential and transition state models for dichlorocarbene addition all agree with the observed regioselectivity.