ELECTROPHILIC REACTIONS OF THE DIBENZO[A,D]TROPYLIUM ION

The kinetics of the hydride transfer reactions of the dibenzotropylium ion (2) with dimethylphenylsilane (5) and triphenylsilane (6) were us ed to determine its electrophilicity parameter E = -0.71. The pi nucle ophiles 7-9 react 10-40 times faster with 2 than expected from the lin ear free energy relationship (1), probably due to the formation of a p i-stabilized carbocation (e.g. 15). A detailed investigation of the re action of 2 with isobutene (4) shows that the linear addition product 13a and the cyclization products are not formed via a common intermedi ate.