Unusually large secondary deuterium isotope effect. Thermal trans-cis isomerization of trans-1-phenylcyclohexene
The magnitudes of secondary deuterium isotope effects (SDIE) are generally in the range of 0.9 < kH/kD < 1.25, and are often satisfactorily rationalized by the zero-point energy (ZPE) change on going from reactant to transition state due to C-H rehybridization. We now report a far larger SDIE for the title reaction. Its rationalization on the basis of transition-state theory suggests that it more closely resembles a primary isotope effect. Laser flash photolysis of cis-1-phenylcyclohexene (direct, 266 nm, or sensitized by thioxanthone, 355 nm) affords its trans isomer which in heptane exclusively reverts to 1, k = 2.1 x 10/sup 5/ s at 300 K. Isotopically substituted 2-2-d1 or 2-2,6-6-d3 (generated similarly from the corresponding cis isomers5) both have rates of reversion longer than 2 itself by a factor of 2.0 at room temperature. No previously reported SDIE approaches this magnitude.
- Research Organization:
- Texas Univ., Austin (USA). Dept. of Chemistry
- OSTI ID:
- 7159802
- Report Number(s):
- AD-A-190891/2/XAB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
ALKANES
ARYL RADICALS
CHEMICAL REACTIONS
CYCLOALKANES
CYCLOHEXANE
DECOMPOSITION
DEUTERIUM
HYDROCARBONS
HYDROGEN ISOTOPES
ISOMERIZATION
ISOTOPE EFFECTS
ISOTOPES
LASERS
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PHENYL RADICALS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADICALS
STABLE ISOTOPES