Chai Y, Xiong X, Yue L, Jiang Y, Pan Y, Fang X. Intramolecular Halogen Transfer via Halonium Ion Intermediates in the Gas Phase.
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2016;
27:161-167. [PMID:
26383734 DOI:
10.1007/s13361-015-1261-4]
[Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2015] [Revised: 08/31/2015] [Accepted: 09/01/2015] [Indexed: 06/05/2023]
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.
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