AbstractThe kinetics of exchange reaction between amide hydrogen atom and acyl group (RCO) in the equimolar mixture of [2‐14C] caprolactam — N‐acylcaprolactam at 150°C without solvent has been studied. The length of the aliphatic chain in the acyl group has no effect on the exchange rate constant kex but branching of this chain increases kex. Hammett's correlation of kex with the Taft constants σ0 was fulfilled. The positive value of the reaction constant shows that the rate of exchange reaction is determined by the extent of the positive charge localized on the carbonyl carbon atom of the acyl group. The mechanism of the reaction involving the occurence of an intermediate product with protonated acyl group in its centre is discussed.