Preparation, 13C NMR/DFT/IGLO study of benzylic mono- and dications, and attempted preparation of a trication

Substituted benzylic mono- and dications were prepared and investigated by H-1 and C-13 NMR spectroscopy and DFT/IGLO calculations. Combined experimental and theoretical study suggest that the structure la is the major resonance contributor to the 2,4,6-trimethylbenzyl cation 1. Similar results were also found for the 2,4,6-dimethyl-4-tert-butylbenzyl 2 and 2,3,4,5,6-pentamethyIbenzyl cation 3. It was found that the structure 4a is the predominant resonance contributor to the overall structure of 2,6-dimethylmesityldiyl dication 4 wherein the dienyl and allylic cation units are insulated from each other. Similar studies indicate structure 5a as the predominant canonical structure for 5-methoxy-2,6-dimethyl-m-xylyldiyl dication 5 wherein the dienyl and oxoallylic cation units are insulated from each ether. Attempts to generate the 2,3,5,6-tetramethyl-1,4-dimethylbenzenediyl dication 8 was, however, not successful as were the generation of the 2,4,6-trimethylmesityltriyl trication 10 by ionization of 2,4,6-bis(chloromethyl)mesitylene. The resulting ion was characterized as a chloromethyl substituted dication 9.