o-, m-, and p-benzyne negative ions in the gas phase: Synthesis, authentication, and thermochemistry
- Purdue Univ., West Lafayette, IN (United States)
The isomeric m- and p-benzyne anions have been generated in the gas phase in a flowing afterglow-triple quadrupole instrument from the reactions of molecular fluorine (F{sub 2}) with m- and p-(trimethylsilyl)phenyl anions. The mechanism of the F{sub 2} reaction involves electron transfer from the (trimethylsilyl)phenyl anion to F{sub 2}, followed by nucleophilic attack on the resulting (trimethylsilyl)phenyl radical by the nascent F{sup -} formed within the intermediate ion/molecule complex. The structures of o-, m-, and p-benzyne anion are unambiguously identified by a classical derivatization scheme. Estimates of the electron affinities of m- and p-benzyne have been determined by the kinetic method. Adducts of SO{sub 2} with phenide ion and each of the isomeric benzyne anions are formed that produce measurable yields of SO{sub 2}{sup .-} and the corresponding C{sub 6}H{sub n}{sup -} ion upon CID. A calibration relation is derived between the CID yield ratios obtained for the C{sub 6}H{sub 5}SO{sub 2}{sup -} and o-C{sub 6}H{sub 4}SO{sub 2}{sup .-} adducts and the known electron affinities of phenyl radical (25.3{+-}0.1 kcal/mol) and o-benzyne (12.9{+-}0.2 kcal/mol). The measured CID ratios for the m- and p-benzyne SO{sub 2} adducts are then combined with this relation to obtain EA(m-benzzyne) = 19.5{+-}0.3 kcal/mol and EA(p-benzyne) = 28.8 {+-} 0.5 kcal/mol. These data are used to derive gas-phase acidities for the different ring positions of phenyl radical and the corresponding C-H bond strengths for the phenide ion ({Delta}H{sub acid}(C{sub 6}H{sub 5}), DH{sub 298}[C{sub 6}H{sub 4}{sup -}-H], kcal/mol). 41 refs., 2 figs., 1 tab.
- OSTI ID:
- 437398
- Journal Information:
- Journal of the American Chemical Society, Vol. 118, Issue 47; Other Information: PBD: 27 Nov 1996
- Country of Publication:
- United States
- Language:
- English
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