Hydrogen atom abstraction from substituted toluenes by tert-butoxy radical

1968 ◽  
Vol 46 (16) ◽  
pp. 2752-2754 ◽  
Author(s):  
R. D. Gilliom ◽  
J. R. Howles
Keyword(s):  
Hydrogen Atom ◽  
Polar Effect ◽  
Hydrogen Atom Abstraction ◽  
Methyl Group ◽  
Tert Butyl ◽  
Hammett Correlation ◽  
Substituted Toluenes ◽  
Butoxy Radical

The relative rates of abstraction of benzylic hydrogen from substituted toluenes by tert-butoxy radicals generated from tert-butyl hypochlorite have been reexamined. Abstraction from para-methylanisole was shown to occur at the ether methyl as well as at the benzylic methyl group. For this reason the compound was excluded from an analysis of the polar effect. A slightly better Hammett correlation was obtained using sigma rather than sigma-plus values.

REACTIONS OF ALKOXY RADICALS: I. HYDROGEN ATOM ABSTRACTION FROM SUBSTITUTED TOLUENES

1966 ◽  
Vol 44 (20) ◽  
pp. 2381-2385 ◽  
Author(s):  
B. R. Kennedy ◽  
K. U. Ingold
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Atom Abstraction ◽  
High Electron ◽  
Hammett Equation ◽  
Alkoxy Radicals ◽  
Benzyl Radical ◽  
High Electron Affinity ◽  
Stabilizing Effect ◽  
Substituted Toluenes ◽  
Butoxy Radical

The relative rates of hydrogen atom abstraction from ten substituted toluenes by t-butoxy radicals in carbon tetrachloride at 40 °C have been measured and the data fitted to the Hammett equation. A much better correlation is obtained with the σ+ constants than with the σ constants of the substituents. In this respect, therefore, the reaction is similar to the majority of hydrogen atom abstraction reactions by radicals of moderate and high electron affinity. That is, the polar properties of the substituents are much more important than their stabilizing effect on the benzyl radical formed in the reaction.The cumyloxy radical has a similar reactivity to the t-butoxy radical. The p-nitrocumyloxy radical appears to be slightly more reactive and also slightly more susceptible to the polar effects of substituents than are t-butoxy or cumyloxy radicals.

Radiation and Radiationless Processes in 2,3-Pentanedione; Phosphorescence Lifetime in the Gas Phase

1971 ◽  
Vol 49 (7) ◽  
pp. 987-993 ◽  
Author(s):  
A. W. Jackson ◽  
A. J. Yarwood
Keyword(s):  
Hydrogen Atom ◽  
Triplet State ◽  
Gas Phase ◽  
Ground State ◽  
Hydrogen Atom Abstraction ◽  
Intersystem Crossing ◽  
Phosphorescence Lifetime ◽  
Gaseous State ◽  
Methyl Group ◽  
Intramolecular Hydrogen

Fluorescence and phosphorescence are observed when 2,3-pentanedione in the gaseous state is excited at 365, 405, and 436°nm. The phosphorescence lifetime has been investigated as a function of temperature (298 to 363 °K) and concentration of the diketone (0.5 to 90 × 10−4 M). A mechanism that explains the experimental data is proposed. Apart from the radiative process and an intersystem crossing to the ground state, the triplet state 2,3-pentanedione molecules are removed by two other processes. One is a unimolecular reaction with a rate constant of 1 × 1011 exp (−11.0/RT) s−1 (consistent with an intramolecular hydrogen atom abstraction), and the other is an interaction with ground state molecules. The photochemistry of the triplet state of 2,3-pentanedione is compared with that of biacetyl to consider the effect of substitution of a hydrogen atom by the methyl group on the radiationless processes in diketones.

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