ELECTRONIC-STRUCTURE STUDIES OF 1,2-DIDEHYDROGENATION OF ARENES AND REARRANGEMENT OF ARYNES TO ANNELATED CYCLOPENTADIENYLIDENECARBENE

CCSD(T)/6-311G* electronic structure calculations confirm the experim entally postulated existence of cyclopentadienylidenecarbene (CPDC) an d verify the reliability of the BLYP/6-311G* predictions for thermoch emistry and kinetics of the 1,2-didehydrogenation of arenes and the ri ng contraction of the resulting arynes. The former process is found to possess low site specificity, its energetics being influenced mostly by steric overcrowding of hydrogens. On the other hand, the energetics and barriers of rearrangements of higher arynes to annelated CPDCs ar e determined by the nature of bonding in the reaction products. Three distinct types of isomerizations, of which only one is observed experi mentally, are readily recognizable.