Structural characterization and thermochemistry of reactive organic intermediates

Loubna Hammad, Purdue University

Abstract

The enthalpy of formation of m-quinodimethane ( m-xylylene) has been determined using two different gas-phase approaches. The first involves combining the electron affinity of the biradical with the acidity of the 3-methylbenzyl radical. The second approach involves using collision-induced dissociation (CID) threshold energy measurements with the 3-(chloromethyl)benzyl ion. The enthalpy of formation of m-xylylene was determined to be 81.2 ± 3.0 kcal/mol indicating a benzylic C-H bond dissociation energy in m-xylyl radical of 90.7 ± 2.9 kcal/mol which is indistinguishable from the C-H BDE of toluene. The heat of formation of 1,3,5-trimethylenebenzene triradical was measured by CID of the 5-chloromethyl-m-xylylene ion. The measured CID threshold energy for chloride loss (0.83 ± 0.07 eV) is combined with the electron affinity of the 5 chloromethyl-m-xylylene biradical (1.120 ± 0.059 eV) to give a heat of formation of the triradical of 111.0 ± 4.1 kcal/mol. The measured heat of formation indicates a third C-H bond dissociation energy in 1,3,5-trimethylbenzene of 88.2 ± 5.0 kcal/mol, indistinguishable from the C-H BDE in toluene. The Cope cyclization of a radical anion was shown to occur in the gas-phase. Reactivity studies on the molecular anion of 2,5-dicyano-1,5-hexadiene are consistent with a cyclic structure for the ion demonstrating that 2,5-dicyano-1,5-hexadiene spontaneously cylizes upon reduction in the gas-phase.

Degree

Ph.D.

Advisors

Wenthold, Purdue University.

Subject Area

Organic chemistry

COinS