Loss of H2O from M + t‐Butyl Complex Ions of Benzyl Alcohol in Isobutane Chemical Ionization Mass Spectrometry

Abstract

AbstractIn isobutane chemical ionization mass spectrometry benzyl alcohol exhibits ions at m/z 147 (‘M + 39’) that arise by a loss of H2O from [M + C4H9]+, i.e. ‘M + 57’ complex ions. Electrophilic aromatic substitution of a proton at an ortho‐position of neutral C6H5CH2OH with [t‐C4H9]+ and, alternatively, nucleophilic substitution of H2O at the benzylic carbon in \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C_6 H_5 CH_2}\mathop {\rm O}\limits^+ {\rm H}_2 $\end{document} with CH2C (CH3)2 are discussed as possible pathways. Evidence in favor of the latter is derived from the analysis of C6D5CH2OH and C6H5CD2OH for the origin of the H‐atoms lost in H2O. The inferred ion structure of m/z 147 is verified by mass‐analyzed ion kinetic energy (MIKE.) measurements of its collision‐activated (CA.) decomposition. MIKE./CA. spectra of mass‐selected m/z 147 ions, once generated by (CI(i‐C4H10) from benzyl alcohol and, once, from 2‐methyl‐4‐phenyl‐2‐butanol match closely and, thus, reflect identical ion structures. With reference to the simple genesis of this ion from the latter precursor, the structure in question can be concluded to be \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C_6 H_5 CH_2 CH_2}\mathop {\rm C}\limits^+ ({\rm CH}_3)_2 $\end{document} .