Abstract

We propose that a specific property of a chemical fragment, its regional electrophilicity, be taken as defining its nucleofugality index ?(PG) in ?-elimination reactions. We tabulate this quantity for a series of molecular fragments present as leaving groups in a series of 17 ?-elimination reactions that follow the E1cB or BAC 2 mechanisms. The difference in the nucleofugality index assesses well the type of mechanism which is operative: a large positive or negative difference in nucleofugality discriminates well between the E1cB and BAC 2 channels, respectively, whereas the region for which this difference is small correctly describes the borderline zone. © 2007 Elsevier B.V. All rights reserved.