AN AB-INITIO QUANTUM-CHEMICAL STUDY OF THE ELECTRONIC-STRUCTURE AND STABILITY OF THE PYRROLYL RADICAL - COMPARISON WITH THE ISOELECTRONIC CYCLOPENTADIENYL RADICAL

The electronic structure and stability of pyrrolyl are investigated us ing CASSCF, CASPT2 and G2(MP2) techniques. The ground state of pyrroly l is found to be (2)A(2), With five pi-electrons, as in cyclopentadien yl. The computed N-H bond energy of pyrrole is 94.8 kcal mol(-1), whil e the heat of formation Delta(f)H(298)degrees of pyrrolyl is deduced t o be 70.5 +/- 1 kcal mol(-1). The Arrhenius parameters of N-H and C-H bond fission in pyrrole and cyclopentadiene and hydrogen abstraction r eactions (by hydrogen) were also computed, indicating that pyrrolyl fo rms predominantly by C-K bond fission of pyrrolenine rather than by di rect N-H bond fission. (C) 1998 published by Elsevier Science B.V. All rights reserved.