CATALYTIC CHEMISTRY OF FURAN AND THIOPHENE - AB-INITIO CALCULATIONS, USING THE SPIN-COUPLED VALENCE-BOND METHOD, OF THE INTERACTION OF FURAN AND THIOPHENE WITH A POSITIVELY CHARGED CENTER

The spin-coupled valence bond (SC-VB) method is summarized and used to determine the electronic structure of furan and thiophene. The result ing wavefunctions are utilized in a study of the interaction of these molecules with an approaching Li+ ion. It is found that the SC-VB desc ription of the lone pairs of the heteroatoms provides a coherent expla nation of the unusual fact that, in the minimum-energy structure of th e thiophene-Li+ complex, the Li+ ion lies off the C-2 axis (at an angl e of 50 degrees), whereas for the furan complex the Li+ ion lies on th e C-2 axis. It is suggested that the interactions are sufficient to co nstrain the molecules at a positive centre on the surface of a catalys t without developing such strong bonds that the catalyst would be pois oned. The implications of this description for the catalytic activatio n of thiophene by transition-metal ions are discussed.