N-Chloro-alpha-amino　acids　formed　in　the　chlorination　disinfection　treatment　of　water　or　wastewater　and　in　living　organisms　have　attracted　extensive　attention　due　to　the　potential　toxicities　of　themselves　and　their　decomposition　products.　The　degradation　mechanisms　of　three　N-chloro-alpha-amino　acids,　i.e.,　N-chloro-glycine,　N-chloro-alanine,　and　N-chloro-valine,　have　been　systematically　investigated　using　quantum　chemical　computations.　The　results　indicate　that　N-chloro-alpha-amino　acid　anions　undergo　two　competitive　degradation　pathways:　a　concerted　Grob　fragmentation　(CGF)　and　beta-elimination　(beta-E).　Generally,　the　former　predominates　over　the　latter　under　neutral　conditions　and　finally　generates　amines　and　carbonyls,　while　the　latter　is　preferred　under　base-promoted　conditions　and　mainly　produces　the　respective　alpha-keto　acid　anions　or　nitriles　in　the　end.　To　gain　deeper　insights　into　the　substitution　effects,　in　view　of　the　advantages　of　quantum　chemical　computations,　a　number　of　real　or　designed　N-chloro-alpha-amino　acids　with　traditional　electron-donating　groups　(EDG)　or　electron-withdrawing　groups　(EWG)　have　been　studied.　All　of　the　substituted　N-chloro-alpha-amino　acids,　regardless　of　the　type　and　position　of　substituents,　are　kinetically　more　favorable　than　N-monochloro-glycine　for　degradation　via　the　CGF　pathway.　Moreover,　conjugated　EDG　substituted　on　the　N-terminal　facilitate　both　CGF　and　beta-E　reactions,　whereas　conjugated　EDG　and　EWG　on　the　alpha-carbon　are　only　favorable　for　the　CGF　and　beta-E　reactions,　respectively.　These　results　are　expected　to　expand　our　understanding　of　organic　N-chloramine　degradation　mechanisms　and　chlorination　reaction　characteristics.