BENZYL, 9-FLUORENYL AND DIPHENYLMETHYL CATIONS - STRUCTURES AND RELATIVE STABILITIES BASED ON HYDRIDE TRANSFER-REACTIONS

Ab initio molecular orbital calculations are reported at HF/6-31G(d,p) and MP2(fc)/6-31G(d) for the diphenylmethyl (I), 9-fluorenyl (II) and benzyl (III) cations, and for the hydrocarbons diphenylmethane (IV), fluorene (V) and toluene (VI). Structure optimisations have been perfo rmed at both levels of theory and all critical points were characteris ed by harmonic frequency calculations at the Hartree-Fock level. Based on hydride transfer reactions, one phenyl group is calculated to stab ilise the methyl cation by 74.3 kcal mol(-1), and a second phenyl adds a further stabilisation of 25.1 kcal mol(-1). The 9-fluorenyl cation is intermediate in stability between the diphenylmethyl and benzyl cat ions, but is closer to the diphenylmethyl cation.