水自由基阳离子与苯及其衍生物反应的质谱研究OA北大核心CSTPCDEI

Study of chemical properties of water radical cations is of great significance for elucidating related reactions process.In this paper,the reaction characteristics of(H2O)2+·prepared online with several benzene derivatives were investigated.The results showed that,when(H2O)2+·reacted with aromatic compounds without electron-withdrawing groups,such as benzene(C6H6,78 u),anisole(C7H8O,108 u)and 2,4-dimethylaniline(C8H11N,121 u),the corresponding phenol product((C6H5OH)+·,m/z 94),(C7H7O-OH)+·,m/z 124)and(C8H10NOH+H)+,m/z 138))were observed,accompanied with the production of electron transfer(ET)products(C6H6)+·,(C7H8O)+·)or proton transfer(PT)product((C8H11N+H)+).Isotope labeling experiments proved that OH in corresponding phenol products was originated from(H2O)2+·.Interestingly,when(H2O)2+·reacted with substituted benzenes bearing strong electron-withdrawing group,such as benzonitrile(C6H5CN,103 u)and nitrobenzene(C6H5NO2,123 u),the main products were the radical substituted adducts(C6H5CN+H2O)+·(m/z121)and(C6H5NO2+H2O)+·(m/z141),respectively,without phenol products or substituted benzene radical cation were noticed.It was obvious that the reaction between(H2O)2+·and the substrate occurred through four competing processes:(a)electron transfer(ET)reaction,in which aromatic compounds release an electron to(H2O)2+·to from an aromatic radical cation;(b)proton transfer(PT)reaction in which aromatic compounds got a proton derived from the dissociation of(H2O)2+·;(c)dissociative electron transfer(DET)reaction,accompanied with the electron transfer process,C-H bond cleavage and C-OH bond formation;(d)radical substitution reaction in which a radical cation adduct consisting of aromatic molecule and H2O generates.It was speculated that the diverse reactivity of(H2O)2+·was owe to its two interchange structures((H2O)H+-·OH and[H2O∴OH2]+·)generates.It was proposed that the electron withdrawing groups on the aromatic ring would benefit for the existence of two-center and three-electron structure of(H2O)2+·and induced the radical substitution reaction.In contrary,compounds without electron withdrawing groups or bearing electron donating groups on the aromatic ring would contribute to the presence of proton transfer structure of(H2O)2+·(containing H+and·OH)and facilitate the C-OH bond formation.This study will help to elucidate the chemical reaction processes involving benzene or substituted benzenes and(H2O)2+·.