Fluoro and chloro-containing compounds which include carbonyls, nitriles, nitro compounds and sulfones make up a notable fraction of publications but an even larger proportion of covalent inhibitors (Figure ). The ready availability of chloroacetylating agents and the modularity of chloroacetamides likely allows for the rapid synthesis of chloro-containing covalent inhibitors by adaptation of noncovalent inhibitors accounting for the rapid growth in publications in the last decade (Figure ). The greater stability of chloro-containing covalent inhibitors to storage than bromo-and iodoacetyl compounds accounts for the preference for chloro-containing carbonyl compounds over other halocarbonyl compounds which show a slower growth (Figure ). While the potential reactivity of chloroacetamides with both amines and thiols requires disambiguation, the lack of steric hindrance and flexibility in reactive conformation may make them attractive for covalent inhibitor development.