Synthesis and characterization of reactive intermediates: The study of biradical, carbene, nitrene and carbyne negative ions in the gas phase
Abstract
The synthesis and characterization of carbene, nitrene, carbyne and biradical negative ions were studied using the flowing afterglow-triple quadrupole apparatus. These include the negative ions of phenylcarbene, 3-ethoxyphenylnitrene, phenylcarbyne and 2,4-dimethylenecyclobutane-1,3-diyl, respectively. Various experimental gas-phase acidities, electron affinities and halide dissociation energies were combined in thermochemical cycles to derive the heats of formation of phenylcarbene, phenylcarbyne, and 2,4-dimethylenecyclobutane-1,3-diyl to be 103.8 ± 2.2, 142 ± 4 and 125 ± 4.1 kcal/mol, respectively. Dramatic deviations from bond additivity were observed in the experimental heats of formation of phenylcarbyne and 2,4-dimethylenecyclobutane-1,3-diyl. The measured heats of formation of phenylcarbene and phenylcarbyne were used to derive the last two bond dissociation energies of toluene. Distonic carbene and nitrene ions such as 3- and 4-oxyphenylcarbene and 3-oxyphenylnitrene negative ions were synthesized in the gas phase from the same diazirine and/or azide precursors used to generate carbenes and nitrenes in condensed phase experiments. All negative ions were characterized by examining their unique ion/molecule reactivity and energetics in conjunction with theoretical studies. The reactions of 3-oxyphenylcarbene radical anion were indicative of a ground state singlet, whereas the reactivity of 3-oxiphenylnitrene radical anion was consistent with a ground state triplet. Using the kinetic method, the gas-phase acidities of 3-hydroxyphenylcarbene, m-benzoquinomethane and 3-hydroxyphenylnitrene were found to be 343.1 ± 1.0, 372.3 ± 1.9 and 346.0 ± 1.4 kcal/mol, respectively Finally, m-phenylene-(bis)nitrene radical anion was synthesized by simple electron ionization on m-diazidobenzene. The ion exhibits both neutral nitrene reactivity and reactions due to the nitrene radical anion site. This distonic ion is a particularly interesting species for photoelectron studies.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Organic chemistry|Chemistry
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