A selected ion flow tube study of the reactions of H 3O +, NO + and O 2[rad]+ with a series of C 5, C 6 and C 8 unsaturated biogenic alcohols

Abstract

The rate constants and product ion distributions of the reactions of H 3O +, NO + and O 2 + with 1-penten-3-ol, cis- and trans-2-penten-1-ol, 3-methyl-2-buten-1-ol, 3-methyl-3-buten-1-ol, 2-methyl-3-buten-2-ol, cis- and trans-2-hexen-1-ol, cis- and trans-3-hexen-1-ol, 1-octen-3-ol and 6-methyl-5-hepten-2-ol have been determined at 150 Pa and 295 K using a selected ion flow tube (SIFT). All reactions were found to proceed at a rate close to the collision rate, calculated with the Su and Chesnavich model, using the polarizability and electric dipole moment of the compounds derived from B3LYP/aug-cc-pVDZ quantum chemical calculations. All H 3O + ion/molecule reactions proceed mainly by elimination of a water molecule after protonation. Therefore, the H 3O + precursor ion is not suited to distinguish isomers by the chemical ionization technique in samples, containing several of the C 5 (C 6 or C 8) unsaturated alcohols. The NO + reactions are generally characterized by several reaction pathways, such as hydride and/or hydroxide ion transfer and/or non-dissociative charge transfer and/or three-body association. The SIFT-MS spectra of the ion/molecule reactions of O 2 + with the unsaturated alcohols also show multiple ionic products. Based upon the measured product ion distributions, it can be concluded that in some particular cases the NO + or O 2 + precursor ions are appropriate to identify and quantify isomers in mixtures of the unsaturated alcohols studied. Especially in leaf wounding experiments, during which cis-3-hexen-1-ol and trans-2-hexen-1-ol are emitted, the chemical ionization technique, based upon the NO + or O 2 + precursor ion, may be a valuable diagnostic tool to distinguish and quantify these isomeric forms.