The solvolysis of anilino thioethers, ArN(CH3)CH2SR, in aqueous solution,1and theoretical studies on the gas‐phase stabilities and reactivities of iminium ions2have shown that iminium cations are highly unstable in aqueous solution, with a lifetime of 10−7–10−8s, as well as in the gas phase, but the formation of iminium cations is favored by extensive electron donation from the nitrogen to the antibonding orbital of the leaving bond, nN→σCS*, by a first‐neighbor vicinal charge transfer interaction. In the presence of a strong nucleophilic reagent, a concerted bimolecular nucleophilic substitution (SN2) mechanism is enforced by the absence of a significant lifetime for an iminium cation that is in contact with nucleophiles.1,3We report here the results of our detailed examination of the mechanism of the bimolecular nucleophilic substitution reactions of anilino thioethers, YC6H4N(CH3)CH2SC6H4Z,I, with anilines, XC6H4NH2, in methanol at 45.0°C. In particular we have determined cross‐interaction constants,ρXY,ρYZandρXZ, by subjecting the second‐order rate constants,k2[orkijineqn. (1a)] to multiple regression analysis usingeqn. (1a,b), whereiandjrepresent substituents in the nucleophile (X), substrate (Y) and leaving group (Z):41a1bAn especially interesting finding in the present work is thatρXZhas a large negative value, which has been interpreted to indicate a frontside‐attack SN2 mechanism.5