Magnitude of primary isotope effects for proton abstraction from carbon

Journal Article · Wed Sep 19 04:00:00 EDT 1984 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00331a038· OSTI ID:6461483

Hupe, D J; Pohl, E R

Primary deuterium isotope effects have been measured for the loss of an ..cap alpha.. proton from 4-(4-nitrophenoxy)-2-butanone. The isotope effect data showed that no significant change in transition-state structure occurred in the same region of oxyanion catalyst pK/sub a/ range that does exhibit a large change in ..beta.. value. This conclusion confirms the previous assertion that the dramatic curvature in the Broensted plot for proton abstraction by oxyanions from carbon is due to solvation. The effect upon k/sub H/ / k/sub D/ of varying the identity of the atom acting as the proton acceptor was examined. Catalysts having oxygen, nitrogen, carbon, and sulfur as the acceptor atom were included. An inverse correlation was found between the magnitude of the isotope effect for proton abstraction by X/sup -/ and the energy change upon conversion of HX to DX. With use of the Marcus equation as a basis, an equation was derived for predicting values of k/sub H/ / k/sub D/ which not only relies on the ..delta..pK/sub a/ value but also incorporates the zero-point energy difference of both the reactants and the products as measured by infrared stretching frequency shifts upon deuteration. This equation demonstrates improved correlation between calculated and experimental values of k/sub H/ / k/sub D/ taken from the literature. 48 references.

• Research Organization: Merck Sharp and Dohme Research Laboratories, Rahway, NJ
• OSTI ID: 6461483
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 106:19; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ACETATES
AMINES
AROMATICS
CARBOXYLIC ACID SALTS
CATALYSTS
CHEMICAL REACTIONS
CORRELATIONS
CYANIDES
DATA
DATA ANALYSIS
DEUTERIUM
DEUTERIUM COMPOUNDS
ETHERS
EXPERIMENTAL DATA
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROXIDES
INFORMATION
INFRARED SPECTRA
ISOTOPE EFFECTS
ISOTOPE RATIO
ISOTOPES
KETONES
LIGHT NUCLEI
MATHEMATICAL MODELS
NMR SPECTRA
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXYGEN COMPOUNDS
SPECTRA
STABLE ISOTOPES
THIOLS