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Large intrinsic nuclear magnetic resonance isotope shifts associated with bending motion along the bridging coordinate in carbocations

Journal Article · · J. Am. Chem. Soc.; (United States)
DOI:https://doi.org/10.1021/ja00258a004· OSTI ID:5614826
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Deuterium isotope effects on the /sup 13/C NMR chemical shifts have been determined for the 2-methyl-2-bicyclo(2.2.2)octyl and 2-methyl-2-bicyclo(2.2.1)heptyl cations. These tertiary carbocations have isotope shifts that are larger than 1 ppm per deuterium, which is an order of magnitude larger than ordinary intrinsic shifts found in nonionic model compounds and in other carbocations. For deuteriation at the C/sub 3/ methylene or methyl group, the same pattern occurs in both cations: isotope shifts that are large and upfield at C/sub 2/, downfield at C/sub 1/, and upfield at the remaining carbon directly bonded to C/sub 2/. The similarity in the pattern of the isotope shifts suggests that the force field and shielding influences in both ions are similar. The specific results are interpreted as indicating the presence of a shallow potential surface for the bending motion along the direction associated with sigma-bridging. Since the existence of the shallow potential does not depend on the actual extent of bridging, the magnitude of the isotope effect is not proportional to the extent of bridging.

Research Organization:
Northeastern Univ., Boston, MA
OSTI ID:
5614826
Journal Information:
J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 109:24; ISSN JACSA
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
CARBON 13
CARBON ISOTOPES
CATIONS
CHARGED PARTICLES
CHEMICAL SHIFT
DATA
DEUTERIUM
DEUTERIUM COMPOUNDS
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
INFORMATION
IONS
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
RESONANCE
SPECTRA
SPECTRAL SHIFT
STABLE ISOTOPES
TEMPERATURE DEPENDENCE