Temperature effects on rates of dehalogenation of aromatic anion radicals

Journal Article · Thu Jan 02 04:00:00 EST 1986 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100273a038· OSTI ID:6036656

Meot-Ner, M ^[1]; Neta, P; Norris, R K; Wilson, K

---

1. Mautner

The temperature dependence of the unimolecular dehalogenation of radical anions of nitrobenzyl halides and haloacetophenones was measured between -7 and 70/sup 0/C. Activation parameters range from E/sub a/ = 11.2-16.9 kcal/mol and log A = 12.7-17.1. Both E/sub a/ and log A increase from p- to o-nitro radicals and from chloro to bromo radicals. Unfavorable steric effects that move the halogen atom out of the aromatic plane result in lowered A factors. In general, the variation of k/sub 294/ with structure depends in a complex way on the combination of E/sub a/ and log A factors, which suggests caution in the evaluation of rate constants at one temperature. The fast unimolecular dissociation of (p-NO/sub 2/C/sub 6/H/sub 3/CH/sub 2/Br)/sup -/ . (k/sub 294/ = 4.6 x 10/sup 5/ s/sup -1/) allows measurement of the slower bimolecular electron transfer (C/sub 6/H/sub 5/NO/sub 2/)/sup -/ . + p-NO/sub 2/C/sub 6/H/sub 4/CH/sub 2/Br ..-->.. (p-NO/sub 2/C/sub 6/H/sub 4/CH/sub 2/Br)/sup -/ . + C/sub 6/H/sub 5/NO/sub 2/ (k/sub 294/ = 1.9 x 10/sup 6/ M/sup -1/ s/sup -1/). Both the activation energy and probability factor contribute to the slow rate, possibly due to a geometry change upon the reduction of ArNO/sub 2/. Extending the temperature studies to supercooled solutions shows no discontinuity of the unimolecular rate constants near the phase transition temperatures. 24 references, 4 figures, 1 table.

• Research Organization: National Bureau of Standards, Gaithersburg, MD
• OSTI ID: 6036656
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 90:1; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ACTIVATION ENERGY
ARRHENIUS EQUATION
CHEMICAL REACTION KINETICS
DATA
DISSOCIATION
ENERGY
EQUATIONS
EXPERIMENTAL DATA
INFORMATION
KINETICS
MEDIUM TEMPERATURE
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
REACTION KINETICS
TEMPERATURE DEPENDENCE