4-(Trifluoromethyl)-alpha-bromoacetanilide is structurally similar to a large number of compounds that inactivate alpha-chymotrypsin by alkylating the methionine-192 residue or occasionally serine-195. Fluorine nuclear magnetic resonance (NMR) experiments suggest that this material reacts with the enzyme at two distinct loci. One of these involves alkylation of methionine while reaction at a second site, which does not appear to be near the active site, diminishes the proclivity for reaction at methionine. Solvent effects (H2O/D2O) and fluorine-proton Overhauser experiments indicate that the reporter group attached to methionine closely contacts the protein surface and is thereby shielded from solvent while the CF3 group at the second site is more accessible to solvent.