Gas Phase Reactions of the Cyclic Ethylenehalonium Ions (CH2)2X+ (X = Cl, Br) with Glycine1

The gas phase reactions of glycine with the cyclic ethylenehalonium ions (CH 2 ) 2 X + (X = Cl, Br) A in the CI source of a tandem mass spectrometer reveal a rich chemistry. The mechanisms of these reactions were determined by analyzing the unimolecular fragmentation reactions of the product ions. The major products are consistent with alkylation by (CH 2 ) 2 X + ions to form a [M + C 2 H 4 X] + adduct ion, in which addition to both nitrogen and oxygen occurs, with the former dominating. Independently generated [H 2 NCH 2 CO 2 CH 2 CH 2 X + H] + ions undergo partial isomerization to form [XCH 2 CH 2 NHCH 2 CO 2 H + H] + ions, with isomerization being greatest when X = Br. This, together with the fact that (CH 2 ) 2 X + fragment ions are also observed, is consistent with a neighboring-group mechanism whereby a [(CH 2 ) 2 X + (H 2 NCH 2 CO 2 H)] ion−molecule complex is formed. The [M + C 2 H 4 X] + adduct ions also lose HX to form [M + C 2 H 3 ] + ions, both in the source and under MS/MS conditions. Comparison of the MS/MS spectrum with that of an authentic sample indicates that the most likely structure of this [M + C 2 H 3 ] + ion is that of CH 3 CH NHCH 2 CO 2 H + . These experimental results are consistent with the ab initio calculated (at the MP2(FC)/6-31G*//HF/6-31G* level) relative stabilities of various isomeric [M + C 2 H 3 ] + ions. For (CH 2 ) 2 Br + an additional [M + Br] + ion is observed whose structure, based upon MS/MS studies, is consistent with attachment of Br + onto nitrogen and to a lesser extent onto oxygen. Finally, the structure of a [M + CH 2 NH 2 ] + ion, formed in the source reaction between the primary product ion CH 2 NH 2 + and glycine, was also studied by MS/MS. This ion consists of two types of structures: ion dipole complexes and a covalent structure. The latter eliminates NH 3 to form a [M + CH] + ion of structure CH 2 NHCH 2 CO 2 H + .