CLASSICAL AND NONCLASSICAL ISOMERS OF TROPYLIUM, SILATROPYLIUM, AND GERMATROPYLIUM CATIONS - DESCENDING THE PERIODIC-TABLE INCREASES THE PREFERENCE FOR NONCLASSICAL STRUCTURES

Ab initio calculations at the G2(MP2,SVP) level predict that there is a striking transition from a preference for classical isomers on the C 7H7+ surface to a preference for nonclassical isomers on the C6H7Ge+ s urface. The situation for C6H7Si+ is intermediate between these extrem es, with classical-and nonclassical isomers tending to have comparable energies despite their significant geometric differences.