The influence of electronic factors on the rates of N → N′ aroyl migration in N-aroyl-N-(hetero)aryl ethylenediamines has been examined. Electron-withdrawing substituents on the aroyl group were found to weakly accelerate the reaction (in linear correlation with the Hammett σ_p constants). Much stronger influence came from the nitrogen-bound aromatic group which gave a strong linear correlation with the Hammett σ_p⁻ constants. For electron-deficient heteroaromatics and nitroaromatics, the migration was nearly instantaneous in basic medium. These findings will significantly impact the planning of mechanistically related transformations of N-(2-aminoethyl) lactams through the hydrated imidazoline ring expansion (HIRE) process.