Comparative study of the hypercoordinate carbonium ions and their boron analogs: A challenge for spectroscopists

Theoretical and related experimental studies have shown that carbon can extend its bonding from Kekule’s tetravalent methane to five, six or seven coordinated protonated methanes, i.e., CH5+, CH62+ and CH73+ and their analogs. Ab initio calculations indicate that higher coordinated, highly charged carbonium ions could be viable species despite the substantial charge–charge repulsion. Structure and bonding of such carbonium ions and the isoelectronic boron analogs were studied and are discussed. These contribute to our general understanding of the electrophilic reactivity of C–H and C–C single bonds.