The reactivity of 4-chloro-7-nitrobenzofurazan (NBD-Cl) with two different classes of nucleophiles (namely 4-substituted anilines and thiophenols) has been investigated using density functional theory (DFT) and interpreted using chemical reactivity descriptors. A good correlation between chemical descriptors, such as ionisation potential and nucleophilicity, and reaction rates was found for 4-substituted anilines. On this basis, predictions on the reactivity of 4-substituted thiophenols were drawn. To get further insights on the mechanism, the transition state corresponding to the rate determining step was characterized for each reaction and the barrier heights related to the experimental reaction rates and the computed chemical descriptors. (C) 2008 Elsevier B.V. All rights reserved.