Deuterium and oxygen-18 isotope effects on nucleophilic displacement by monomeric water in aprotic solvents
The H/sub 2/O/D/sub 2/O rate-constant ratio for nucleophilic attack by water at a methyl carbon (eq 1) is reduced to very near unity when the water is a dilute solute in L/sub 2/O+CH/sub 3/X..-->..L/sub 2/O/sup +/CH/sub 3/+X/sup -/ a dipolar aprotic solvent. This effect was observed for three leaving groups (CH/sub 3/X equals 1-methylthiophenium ion (MeTh/sup +/), methyl perchlorate (MeOCl/sub 3/), and methyl trifluoromethanesulfonate (MeOTf)) and for two aprotic solvents acetonitrile (MeCn), and tetrahydrothiophene 1,1-dioxide (TMSO:'';sulfolane). It was also observed that the corresponding H/sub 2//sup 16/O/H/sub 2//sup 18/O rate-constant ratio is 1.002 +- 0.004 (95% confidence limits) for the reaction of MeTh/sup +/ with dilute H/sub 2/O in TMSO/sub 2/ at 35/sup 0/C. Although alternative explanations exist (vide infra), these observations are consistent with a mechanism in which no significant positive charge is present on the L/sub 2/O oxygen in the rate-determining transition state and thus in which the rate-determining process does not involve (and is not preceded by) any significant covalent-bonding interaction between the nucleophile and the methyl carbon. All reactions were followed by uv spectroscopy in a Cary 16K spectrophotometer.
- Research Organization:
- Washington Univ., St. Louis, MO
- OSTI ID:
- 5011573
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 102:16
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
DEUTERIUM
ISOTOPE EFFECTS
OXYGEN 18
ABSORPTION SPECTROSCOPY
FLUORINATED ALIPHATIC HYDROCARBONS
HEAVY WATER
HETEROCYCLIC COMPOUNDS
NITRILES
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PERCHLORATES
STRUCTURAL CHEMICAL ANALYSIS
SULFONATES
ULTRAVIOLET SPECTRA
WATER
CHLORINE COMPOUNDS
EVEN-EVEN NUCLEI
HALOGEN COMPOUNDS
HALOGENATED ALIPHATIC HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPES
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
SPECTRA
SPECTROSCOPY
STABLE ISOTOPES
400302* - Organic Chemistry- Isotope Effects- (-1987)