Gas phase reactions of NH2Cl with anionic nucleophiles: Nucleophilic substitution at neutral nitrogen

Reactions of chloramine, NH2Cl, with HO-, RO- (R = CH3, CH3CH2, CH3CH2CH2, C6H5CH2, CF3CH2), F-, HS-, and Cl- have been studied in the gas phase using the selected ion flow tube technique. Nucleophilic substitution (S(N)2) at nitrogen to form Cl- has been observed for all the nucleophiles. The react ions are faster than the corresponding S(N)2 reactions of methyl chloride; the chloramine reactions take place at nearly every collision when the reac tion is exothermic. The thermoneutral identity S(N)2 reaction of NH2Cl with Cl-, which occurs approximately once in every 100 collisions, is more than two orders of magnitude faster than the analogous reaction of CH3Cl. The s ignificantly enhanced S(N)2 reactivity of NH2Cl is consistent with a previo us theoretical prediction that the barrier height for the 5,2 identity reac tion at nitrogen is negative relative to the energy of the reactants, where as this barrier height for reaction at carbon is positive. Competitive prot on abstraction to form NHCl- has also been observed with more highly basic anions (HO-, CH3O-, and CH3CH2O-), and this is the major reaction channel f or HO- and CH3O-. Acidity bracketing determines the heat of deprotonation o f NH2Cl as 374.4 +/- 3.0 kcal mol(-1). (C) 2001 American Society for Mass S pectrometry.