In depth look at selected warheads: α,β-unsaturated carbonyl compounds have the structures C::CCOX (X is an alkoxy group, an amino group, a proton, or an alkyl or aryl group; α,β-unsaturated cyanides may be included where the carbonyl is replaced with a C:::N group). In most cases, the alkene is terminated with a methylene group, CH2; in some cases, one of the protons may be substituted with an alkyl group such as dimethylamino (Me2NCH2) or piperidinylmethyl (C5H10NCH2). Cyclic α,β-unsaturated carbonyl compounds are uncommon in covalent inhibitors, as are cycloalkenyl carbonyl compounds.