Kinetic hydrogen isotope effects in the concerted mechanism for the hydrolysis of acetals, ketals, and ortho esters

Journal Article · Wed Oct 25 00:00:00 EDT 1978 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00490a043· OSTI ID:6425868

Eliason, R ^[1]; Kreevoy, M M

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1. Southwest State Univ., Marshall, MN

The hydrolysis of many ortho esters, and some acetals and ketals, is general acid catalyzed, and in some examples these generate linear Bronsted plots over substantial ranges of catalyst acidity. This suggests that the reaction coordinate is primarily a reorganization of heavy atoms since proton transfer from one oxygen to another has been shown to generate strongly curved Bronsted plots. However, the isotopic fractionation factor for the catalytically active proton in these transition states is substantially less than 1.0; in several examples it is less than 0.5. Such values have been thought to require that the reaction coordinate be largely a motion of the hydrogen giving the low fractionation factor. This dilemma has been resolved by the observation and rationalization of fractionation factors as low as 0.28 for stable, hydrogen bridge-bonded complexes, AHA/sup -/. A similar, bounded coordinate is now suggested for the catalytically active protons in question. This permits the reaction coordinate to be pictured. 3 figures, 2 tables.

• OSTI ID: 6425868
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 100:22
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACETALS
HYDROLYSIS
DEUTERIUM
ISOTOPE EFFECTS
ESTERS
ETHERS
KETONES
PYRANS
AQUEOUS SOLUTIONS
CARBOXYLIC ACIDS
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
DIOXANE
FRACTIONATION
HEAVY WATER
OXONIUM IONS
PROTONS
REACTION INTERMEDIATES
BARYONS
CHARGED PARTICLES
CHEMICAL REACTIONS
DECOMPOSITION
DISPERSIONS
ELEMENTARY PARTICLES
FERMIONS
HADRONS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
IONS
ISOTOPES
KINETICS
LIGHT NUCLEI
LYSIS
MIXTURES
MOLECULAR IONS
NUCLEI
NUCLEONS
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
OXYGEN COMPOUNDS
REACTION KINETICS
SEPARATION PROCESSES
SOLUTIONS
SOLVOLYSIS
STABLE ISOTOPES
WATER
400302* - Organic Chemistry- Isotope Effects- (-1987)