Planar Homotropenylium Cation: A Transition State with Reversed Aromaticity

Christopher M. Gibson, Remco W. A. Havenith, Patrick W. Fowler*, Leonardus W. Jenneskens

*Bijbehorende auteur voor dit werk

OnderzoeksoutputAcademicpeer review

6 Citaten (Scopus)


In contrast to the equilibrium structure of the homoaromatic C-s homotropenylium cation, C8H9+ (1), which supports a pinched diatropic ring current, the C(2)v transition state (2) for inversion of the methylene bridge of 1 is antiaromatic and supports a two-lobe paratropic pi current, as detected by plotting B3LYP/6-31G** ipsocentric current maps. Participation of the bridge CH bonds is crucial for the change in global character of the current in the transition state, as shown by the quenching of its paratropicity on substitution of H by F. Orbital-based arguments allow rationalization of this transition between homoaromaticity and hyper(conjugative) antiaromaticity. More generally, the hyperconjugative ring current in a family of C-2v planar-constrained geometries of (CR2)CN-1HN-1q homoannulenes (R = H, F) can be switched from paratropic (antiaromatic) to diatropic (aromatic) by variation of ring size, charge, and bridge substituent. An orbital-based counting rule accounts for these systematic trends.

Originele taal-2English
Pagina's (van-tot)1395-1401
Aantal pagina's7
TijdschriftJournal of Organic Chemistry
Nummer van het tijdschrift3
StatusPublished - 6-feb-2015

Citeer dit