We propose that a specific property of a chemical fragment, its regional electrophilicity, be taken as defining its nucleofugality index nu(PG) in alpha-elimination reactions. We tabulate this quantity for a series of molecular fragments present as leaving groups in a series of 17 alpha-elimination reactions that follow the E1cB or B-AC(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 ElcB and B-AC(2) channels, respectively, whereas the region for which this difference is small correctly describes the borderline zone. (C) 2007 Elsevier B.V. All rights reserved.