Abstract
The fragmentation of homologous 2-alkanols in t-C 4H 9 + and NH 4 + chemical ionization (CI) mass spectra increases with molecular size. Complementarily, the t-C 4H 9 + and OH − CI spectral stereospecificity decreases from methyl- to butylcyclohexanols and cyclic to steroidal diols. These substrate-size phenomena in near thermoneutral proton-transfer CI are based on a molecular degree-of-freedom (DOF) activation effect, which is similar to DOF assisted largest-alkyl loss in M +. ions, but inverse to DOF stabilization of electron-impact fragment ions. A diagram of substrate internal-energy temperature dependence curves Hv(T) and CI reaction enthalpy levels ΔH r and, secondly, a calculation of critical-molecule percentages are useful quantification attempts of the CI DOF activation effect, for its application to CI spectral problems.
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