Secondary deuterium isotope effects on epoxide methanolysis reactions

Journal Article · Tue Mar 25 23:00:00 EST 1980 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00527a060· OSTI ID:5343787

Hanzlik, R P; Westkaemper, R B

Secondary kinetic deuterium isotope effects have recently come into widespread use as probes of reaction mechanism and transition state structure. Isotopic substitution at the reacting carbon gives rise to the so-called ..cap alpha.. effect due to differences in the energetics of out-of-plane bending of C-H and C-D bonds; these effects are usually interpreted in terms of changes in hybridization at the reacting carbon as the reaction processes. Alternately isotopic substitution at carbons adjacent to the reacting carbon leads to a ..beta.. effect presumably arising from differences in the ability of C-H and C-D bands to interact with orbitals on the reacting carbon by means of hyperconjugation. In connection with mechanistic studies of the epoxide-diol pathway secondary deuterium isotope effects were used to compare epoxidation of olefins by cytochrome P-450 with olefin epoxidation by m-chloroperbenzoic acid. Observations of secondary deuterium isotope effects on the acid-and base-catalyzed methanolysis of p-nitrostyrene oxide, a chemical model system for the epoxide hydrase system were reported. This is the first observation of an ..cap alpha.. effect at the ..beta.. carbon or a secondary effect at a neighboring carbon not attributable to hyperconjugation phenomena. Such effects might be expected but are not observed in the solvolysis of ..beta..-arglethyl tosylates and in the thermal cic-trans isomerization of cyclopropane derivatives. Another interesting result is the parallelism that the major reactions in acid and base both involve late or product-like transition states, while both minor reactions involve early or reactant-like transition states. These studies have shown that secondary deuterium isotope effects provide a sensitive and predictable probe for mechanistic studies of epoxide reactions. 3 tables. (DP)

• Research Organization: Univ. of Kansas, Lawrence
• OSTI ID: 5343787
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 102:7; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ALCOHOLS
DEUTERIUM
EPOXIDES
GLYCOLS
HYBRIDIZATION
HYDROGEN ISOTOPES
HYDROXY COMPOUNDS
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGHT NUCLEI
METHANOL
NUCLEAR REACTIONS
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
SECONDARY REACTIONS
STABLE ISOTOPES