THE FIRST EXAMPLES OF PERSISTENT DIMETHYLDIHYDROPYRENIUM CATIONS - REVERSAL OF RING CURRENT EFFECTS

Diatropic [14]annulene trans-15,16-dimethyldihydropyrene 1 and its 2-b romo (2) and 2-nitro (3) derivatives are transformed into stable parat ropic [12]annulenium ions (dimethyldihydropyrenium cations) by low tem perature protonation with FSO3H-SO2ClF. Strong preference for ipso pro tonation (attack at C-2) is observed with 2 and 3. Stable ion studies provide the first charge delocalization mapping at the periphery of th ese [12]annulenium ions and a comparison with pyrenium cations. The pr edicted (AM1 and PM3) annulenium ion energies and charges are compared with experiment. A theoretical study of 1 and 1H(+) at the RHF/6-31G level is included.