Theoretical Study of Elecron Transfer to Neopentyl Chloride and Phenyl-Substituted Derivatives

D. MARIANO A. VERA, ADRIANA B. PIERINI

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY

Wiley Interscience

Año: 2002 vol. 15 p. 894 - 902

0894-3230

<!-- @page { size: 21.59cm 27.94cm; margin: 2cm } P { margin-bottom: 0.21cm } --> ABSTRACT: Aliphatic halides such as neopentyl, bicycloalkyl and polycycloalkyl halides can be substituted bymechanisms that involve electron transfer (ET) steps. The homogeneous or heterogeneous ET to these compounds follows a concerted dissociative pathway, that is, the C–halogen bond cleaves as the electron is being transferred. The ET to alkyl halides substituted by p-electron acceptors, on the other hand, may follow a stepwise mechanism with radical anions as intermediates. Both mechanistic pathways are analyzed on the basis of AM1, B3LYP and MP2 calculations for neopentyl chloride (6) and its phenyl- and benzyl-substituted derivatives 1-chloro-2-methyl-2-phenylpropane (neophyl chloride, 7) and 1-chloro-2,2-dimethyl-3-phenylpropane (8). The solvent effect wasevaluated with Tomasi’s continuum polarized model. While relatively stable p radical anions appear as intermediates on the AM1 potential surfaces of 7 and 8, B3LYP and MP2 favor a concerted dissociative pathway for these compounds. Based on the B3LYP and MP2 results, it can be concluded that the driving force for the dissociative ET to the three compounds depends mainly on their C—C1 bond dissociation. The strength of the C—C1 bond is similar for 6 and 8 and lower for 7. The difference in the C—C1 bond strength of 7 and 8 is ascribed to differences in the stabilizing effect of the phenyl substituent, through a bridge of variable length, and also to the stability of the radical formed in the cleavage. The theoretical results obtained are of help in the interpretation of the relative experimental reactivity previously obtained for the family. Copyright  2002 John Wiley & Sons, Ltd. KEYWORDS: concerted-dissociative electron transfer; stepwise electron transfer; neopentyl halides and stabilized derivatives; radical anions; B3LYP; MP2; AM1