Mass spectrometry of quaternary ammoniohexanoates: Intermolecular alkyl transfer during field desorption

Intermolecular alkyl transfer occurs during field desorption of quaternary ammoniohexanoates, resulting in mass spectra containing structurally diagnostic adduct ions. Methyl, ethyl and propyl groups attached to nitrogen readily undergo intermolecular transfer to give [M+CH₃]⁺, [M+C₂H₅]⁺ and [M+C₃H₇]⁺ ions, respectively. Evidence is presented that alkyl groups even as large as C₁₀H₂₁ can transfer intermolecularly at high emitter temperatures. In addition to the alkyl ion adducts, the field desorption spectra of documentclass{article}pagestyle{empty}begin{document}$ {rm C}_{10} {rm H}_{21} mathop {rm N}limits^ + left({{rm CH}_3 } right)_2 left({{rm CH}_2 } right)_5 {rm COO}^ - $end{document} show several other adduct and fragment ions whose relative intensities depend strongly on emitter current. The field desorption results are compared with earlier pyrolysis electron impact results on similar compounds.