Deuterium isotope effects on the carbon-13 chemical shifts of carbocations
The deuterium isotope effect on the carbon-13 NMR spectrum of several carbocations and neutral molecules have been examined. The carbon-13 resonance of the cationic carbon atom in the heavy isotopomer of the carbocations was found to be shifted upfield, to be unaffected, or to be shifted downfield, upon ..beta..-deuteration from the corresponding carbon in the nondeuterated compound. These effects ranged from -2.5 ppm to +1.6 ppm and were found to be consistent with previous work of Servis and Shue. The two bond chemical shift isotope effects determined for 2-methyl-2-norbornyl cation and for 2-(3,5-bis-(trifluoromethyl)-phenyl)-2-norbornyl cation provide evidence for partial delocalization of positive charge away from C2 into a three-center two-electron bond. The deuterium isotope effects determined for the 2-(p-fluorophenyl)-2-norbornyl cation and the 2-phenyl-2-norbornyl cation provide evidence about the stereochemical dependence of the two bond chemical shift isotope effect. The effect of exo C3 deuterium substitution on the C2-resonance in the carbon-13 NMR spectrum of the 2-(p-fluorophenyl)-2-norbornyl cation and the 2-phenyl-2-norbornyl cation is small and positive while the effect of endo C3 deuterium substitution is small and negative. This is the first case reported in which stereochemically distinct isotope effects at the same carbon are of opposite sign. The two bond chemical shift isotope effects determined for 2,3-dimethyl-2-butene bromonium ion and for 2,3-dimethyl-2-butene mercurinium ion permit the elucidation of the electronic structure of these cations.
- Research Organization:
- University of Southern California, Los Angeles (USA)
- OSTI ID:
- 6036331
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400302 -- Organic Chemistry-- Isotope Effects-- (-1987)
ALKENES
CARBON 13
CARBON ISOTOPES
CATIONS
CHARGED PARTICLES
CYCLOALKENES
DEUTERIUM
EVEN-ODD NUCLEI
HYDROCARBONS
HYDROGEN ISOTOPES
IONS
ISOTOPE APPLICATIONS
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
NMR SPECTRA
NORBORNADIENE
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
SPECTRA
STABLE ISOTOPES
TRACER TECHNIQUES