AbstractThe acidolytic cleavage of a series of new N‐aralkyloxycarbonyl protecting groups has been found to proceed as a first‐order reaction, the rate of cleavage being dependent on the stability of the corresponding aralkyl carbonium ions. Some of the groups are cleaved at much the same rate as the N‐trityl residue and up to 60000 times faster than thet‐butyloxycarbonyl (Boc) group. The rate is also strongly influenced by the acidity of the reaction media. The relative rates at which aralkyloxycarbonyl and Boc groups are split off can be largely controlled by appropriate selection of the reaction conditions.The implications of these findings for peptide syntheses are discussed and the use of the 2‐(p‐diphenyl)‐isopropyloxycarbonyl residue as an especially suitable N‐protecting gr