Rate data are reported for the reactions of 1-fluoro-2,4,6-trinitrobenzene (picryl fluoride) with a series of ortho alkyl substituted anilines (Y = H, 2-CH₃, 2-C₂H₅­, 2,4-(CH₃)₂, 2,6-(CH₃­)₂ or 2,6-(C₂H₅)₂) in acetonitrile. The results are compared with those reported for the corresponding phenoxy derivatives. The kinetic data show that increasing substitution sterically inhibits nucleophlic attack by anilines and a ‘late’ transition is likely. In general, the reactions are base catalyzed, interpreted as rate-limiting deprotonation of the zwitterionic intermediate. The reactions with aniline, 2-methyl and 2,4-dimethyl aniline where steric effects are likely to be small proceed exclusively by the base-catalysed step, while those with the more sterically hindered anilines (Y = 2-C₂H₅, 2,6-(CH₃)₂, 2,6-(C₂H₅)₂), involve both the uncatalysed and the base catalysed pathways. Values of k₁, the rate constant for nucleophilic attack at the 1-position, are higher for picryl fluoride than for the phenoxy analogue due to lower steric requirements and higher electron withdrawal of the fluorine atom than the phenoxy group. Similarly, values of k_An/k_-1 are increased relative to those of the phenoxy derivative. This is likely to reflect increases in the values of k_-1 due to release of steric strain present in the intermediate coupled with decreases in the values of k_An for proton transfer from the zwitterionic intermediate to base due to increased crowding at the reaction centre in the case of the phenoxy compound. The present work sheds further light on the dichotomy regarding the differing reactivities of substituted anilines of comparable basicity.