title: Intramolecular Halogen Transfer via Halonium Ion Intermediates in the Gas Phase.
abstract: The fragmentation of halogen-substituted protonated amines and quaternary ammonium ions (R(1)R(2)R(3)N(+)CH2(CH2)nX, where X = F, Cl, Br, I, n = 1, 2, 3, 4) was studied by electrospray ionization tandem mass spectrometry. A characteristic fragment ion (R(1)R(2)R(3)N(+)X) resulting from halogen transfer was observed in collision-induced dissociation. A new mechanism for the intramolecular halogen transfer was proposed that involves a reactive intermediate, [amine/halonium ion]. A potential energy surface scan using DFT calculation for CH2-N bond cleavage process of protonated 2-bromo-N,N-dimethylethanamine supports the formation of this intermediate. The bromonium ion intermediate-involved halogen transfer mechanism is supported by an examination of the ion/molecule reaction between isolated ethylenebromonium ion and triethylamine, which generates the N-bromo-N,N,N-triethylammonium cation. For other halogens, Cl and I also can be involved in similar intramolecular halogen transfer, but F cannot be involved. With the elongation of the carbon chain between the halogen (bromine as a representative example) and amine, the migration ability of halogen decreases. When the carbon chain contains two or three CH2 units (n = 1, 2), formal bromine cation transfer can take place, and the transfer is easier when n = 1. When the carbon chain contains four or five CH2 units (n = 3, 4), formal bromine cation transfer does not occur, probably because the five- and six-membered cyclic bromonium ions are very stable and do not donate the bromine to the amine.
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou, 310027, China.|College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, China.
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Chai
authors.affiliation: National Institute of Metrology, Beijing, 100013, China.
authors.forename: Xingchuang
authors.initials: X
authors.lastname: Xiong
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Yue
authors.affiliation: National Institute of Metrology, Beijing, 100013, China.
authors.forename: You
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou, 310027, China. panyuanjiang@zju.edu.cn.
authors.forename: Yuanjiang
authors.initials: Y
authors.lastname: Pan
authors.affiliation: National Institute of Metrology, Beijing, 100013, China. fangxiang@nim.ac.cn.
authors.forename: Xiang
authors.initials: X
authors.lastname: Fang
mesh_terms: D005740:Gases / Q000737:chemistry*; D006219:Halogens / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D005740:Gases; D006219:Halogens
keywords: Fragmentation; Halonium ion; Intramolecular halogen transfer; Mass Spectrometry