Isotope effects in hydrogen atom transfer. VII. Benzylic hydrogen abstraction by tert-butoxy and other radicals
Chlorination of toluene by tert-butyl hypochlorite involves the attack of t-BuO on the benzylic hydrogen; isotope effects can be measured by comparing the activity of the product t-BuOH with that of PhCH/sub 3-t/. At 40/sup 0/C, k/sub H//k/sub T/ = 11.5; substituted toluenes give similarly rather large values of k/sub H//k/sub T/, which increase slightly with sigma. In contrast, Cl attack gives k/sub H//k/sub T/ = 3.7, in rough agreement with earlier deuterium effects. Literature values for the isotope effect in the nearly equally exothermic attack by CH/sub 3/ and the more exothermic attack by C/sub 6/H/sub 5/ are closer to the t-BuO value than to the Cl value. Earlier large values of isotope effect in bromination are confirmed with tritium. Secondary effects of tritium in the t-BuO attack were measured and are undetectable. It is postulated that the symmetry effect on the isotope effect is important only when one of the elements flanking hydrogen in the transition state is in the second row or beyond. (auth)
- Research Organization:
- Rice Univ., Houston, TX
- OSTI ID:
- 7190873
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 98:8
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BUTOXY RADICALS
CHEMICAL REACTIONS
HYDROGEN
SULFONES
TOLUENE
TRITIUM
ISOTOPE EFFECTS
BROMINATION
CHLORINATION
ALKOXY RADICALS
AROMATICS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CRYOGENIC FLUIDS
ELEMENTS
FLUIDS
HALOGENATION
HYDROCARBONS
HYDROGEN ISOTOPES
ISOTOPES
LIGHT NUCLEI
NONMETALS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
RADICALS
RADIOISOTOPES
YEARS LIVING RADIOISOTOPES
400302* - Organic Chemistry- Isotope Effects- (-1987)