Ab initio and density functional study of the 5-pentacyclo[6.2.1.1(3,6).0(2,7).0(4,10)]dodecyl cation. A symmetrical mu-hydride bridged carbocation

MP2/6-31g(d,p) and B3LYP/6-31g(d,p) calculations for the pentacyclo[6.2.1.1 (3,6).0(2,7).0(4,10)]dodecyl cation reveal two minima on the potential ener gy surface. The most stable minimum is the g-hydride bridged cation 2. The second minimum is the two-electron three-center bonded structure 3. At MP2/ 6-31g(d,p) 2 is only 0.2 kcal/mol more stable than 3, but at B3LYP/6-31g(d, p) this energy difference increases to 3.3 kcal/mol. The energy difference between 2 and 3 is only 3.8 kcal/mol. Solvent effect does not affect these numbers significantly. This low energy barrier may account for the product distribution observed on solvolysis of pentacyclic derivatives. (C) 2001 El sevier Science B.V. All rights reserved.