Isotopic perturbation effects on a single averaged NMR peak: norbornyl cation

Journal Article · Sat Jun 11 04:00:00 EDT 1983 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00349a034· OSTI ID:5555141

Saunders, M; Kates, M R

A variant of the isotopic perturbation method for investigating questions of whether molecules are rapidly equilibrating over low barriers or have symmetric, single-minimum surfaces is reported. To apply it, the /sup 1/H NMR spectrum of monodeuterated norbornyl cation was examined over a higher temperature range than that used previously. It shows an additional peak on the high-field side of the averaged 1,2,6 signal due to perturbation of the average shift of the remaining three protons by an equilibrium isotope effect in the fraction of molecules containing deuterium on carbons 1, 2, or 6. K/sub iso/ was found to vary from 1.66 to 2.14 over the temperature range from -105 to -43/sup 0/C, yielding a value for ..delta..H of 310 +/- 20 cal/mol. Using a model of the equilibrating classical ions and the reported kinetic isotope effects on solvolysis leads to a prediction of a downfield shift for this peak, while the nonclassical ion structure readily accommodates an upfield shift.

• Research Organization: Yale Univ., New Haven, CT
• OSTI ID: 5555141
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 105:11; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
CATIONS
CHARGED PARTICLES
DEUTERIUM
HYDROGEN ISOTOPES
IONS
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
NUCLEAR MAGNETIC RESONANCE
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
RESONANCE
STABLE ISOTOPES