Gas-phase heats of formation of C sub 7 H sub 7 sup + isomers: M-tolyl, p-tolyl, and benzyl ions
- Univ. of North Carolina, Chapel Hill (USA)
The dissociation onsets of C{sub 7}H{sub 7}{sup +} formation from the ionic precursors of benzyl bromide and m- and p-nitrotoluene have been investigated by photoelectron photoion coincidence in order to determine accurate heats of formation of the resulting C{sub 7}H{sub 7}{sup +} ion structures. These parent ions are known to produce 100% benzyl and tolyl ions, respectively. Because the benzyl bromide ion dissociation was found to be rapid, the dissociation onset was determined from the crossover energy in the breakdown diagram and appropriately corrected for the precursor thermal energy. The nitrobenzene ions dissociate slowly near the dissociation onset, so that the thermochemical onset was found by extrapolating the measured decay rates with the RRKM/QET statistical theory. The rate data indicate that p- and m-nitrotoluene ions do not isomerize to a common structure prior to dissociation. This suggests that, the p- and m-tolyl ions also exist as unique structures. However, no information about the o-tolyl ion was obtained. The derived ionic heats of formation were {Delta}H{sub f}{degree}{sub 298} (m-tolyl) = 1054 {plus minus} 10 kJ/mol, {Delta}H{sub f}{degree}{sub 298} (p-tolyl) = 1074 {plus minus} 10 kJ/mol, and {Delta}H{sub f}{degree}{sub 298} (benzyl) = 897 {plus minus} 5 kJ/mol. An upper limit for the heat of formation of C{sub 6}H{sub 4}CH{sub 3}O{sup +}, the NO loss product from the p-nitrotoluene ion, was determined to be 890 kJ/mol. These heats of formation allow the methyl and ring C-H bond energies in the toluene ion to be calculated. They are 2.18 and 3.9 eV respectively. 50 refs., 4 figs., 3 tabs.
- OSTI ID:
- 6974688
- Journal Information:
- Journal of the American Chemical Society; (USA), Vol. 110:17; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BENZYL RADICALS
FORMATION HEAT
ISOMERS
TOLYL RADICALS
EXPERIMENTAL DATA
GASES
NITRO COMPOUNDS
TOLUENE
ALKYLATED AROMATICS
AROMATICS
ARYL RADICALS
DATA
ENTHALPY
FLUIDS
HYDROCARBONS
INFORMATION
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHYSICAL PROPERTIES
RADICALS
REACTION HEAT
THERMODYNAMIC PROPERTIES
400201* - Chemical & Physicochemical Properties