Gas phase ion chemistry of para substituted benzene diazonium ions, their salt clusters and their related phenyl cations

Abstract

Electrospray ionization of the tetrafluoroborate salts of para substituted (chloro, bromo, nitro and methoxy) benzene diazonium ions (XC 6H 4N 2 + where X=Cl, Br, NO 2 and CH 3O) results in the formation of the bare diazonium ion as well as the mixed inorganic/organic salt ions [XC 6H 4N 2 +(XC 6H 4N 2 +BF 4 −) n ] in the positive ion mode and the bare tetrafluoroborate anion and salt ions [BF 4 −(XC 6H 4N 2 +BF 4 −) n ] in the negative ion mode. Tandem mass spectrometry (MS/MS) experiments were carried out on XC 6H 4N 2 +, [XC 6H 4N 2 +(XC 6H 4N 2 +BF 4 −) n ] and [BF 4 −(XC 6H 4N 2 +BF 4 −) n ] ions. ESI/MS and ESI/MS/MS data are presented which provide some support for “magic number” salt clusters observed for each of the four diazonium salts. Collision induced dissociation of XC 6H 4N 2 + ions result in the formation of highly reactive phenyl cations, XC 6H 4 + in all cases. The gas phase reactivity of both XC 6H 4N 2 + and XC 6H 4 + ions towards nine different nucleophiles, NuY (where NuY=H 2O, CH 3OH, CD 3OD, CH 3CN, (CH 3) 2CO, (CD 3) 2CO, CH 3C(O)NHCH 2CH 3, pyrrole and aniline) was examined using a quadrupole ion trap mass spectrometer. While the diazonium ions were generally unreactive towards these nucleophiles, the phenyl cations readily react to yield the energized adducts (XC 6H 4NuY +). These energized adducts undergo several different fragmentation reactions, including an unusual radical loss of the para substituent. The gas phase CID reactions of stabilized adducts (XC 6H 4NuY +) were also examined and fragmented via similar types of reactions. Finally, the unusual radical loss of the para substituent from the adduct O 2NC 6H 4NCCH 3 + was shown to yield the distonic ion C 6H 4NCCH 3 + via its I and CH 2CHCH 2 radical abstraction reactions with allyl iodide.