AbstractThe reactions oftert‐butoxyl radical with someN‐alkyl‐substituted acryl‐ and methacrylamides were investigated at room temperature in benzene by means of the spin trapping technique. 2‐Methyl‐2‐nitrosopropane (BNO) was used as a spin trapping reagent. Thetert‐butoxyl radical was found to undergo both hydrogen‐abstraction fromN‐methyl groups and double bond addition in its reactions withN‐methylacrylamide (NMAm) and withN,N‐dimethylacrylamide. Contrary to this, the benzoylthio radical reacted exclusively with the double bond of NMAm. In the reaction of thetert‐butoxyl radical withN‐methylmethacrylamide (NMMAm), only double bond addition was observed. However, when thetert‐butoxyl radical reacted withN,N‐dimethylmethacrylamide (NDMMAm), it mainly attacked theN‐methyl group of NDMMAm. Thetert‐butyl radical abstracted a hydrogen atom from the α‐methyl group of NMMAm and NDMMAm, keeping theirN‐methyl group unreacted. Furthermore, in the reaction of thetert‐butoxyl radical withN‐propyldimethacryloylamine (NPDMAm) in the presence of BNO, both a methylene radical which was derived from intramolecular cyclopropagation giving a five‐membered ring and a radical derived from the addition to the double bond o