Calculations of isotope effects in elimination reactions: new experimental criteria for tunneling in slow proton transfers

Journal Article · Wed Jan 09 04:00:00 EST 1985 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00287a029· OSTI ID:5863290

Saunders, Jr, W H

Isotope-effect calculations have been carried out on the model reaction CCH/sub 2/CH/sub 2/Cl + OH/sup -/ ..-->.. CCH=CH/sub 2/ + Cl/sup -/ + H/sub 2/O. When the bending motions of the nontransferred ..beta..-hydrogen are coupled with the stretching motion of the transferred ..beta..-hydrogen, a tunnel correction to the secondary ..beta..-hydrogen isotope effect is introduced. The kinetic secondary effect can be larger than the equilibrium secondary effect, in agreement with recent experiments. The contribution of tunneling to the secondary kinetic effect decreases with increased mass of the transferred atom. Deviations from the expected relation between deuterium and tritium isotope effects, both primary and secondary, can occur when tunneling is important, and are large enough to observe easily when k/sub H//k/sub D/ (or K/sub H//k/sub T/) calculated from k/sub D//k/sub T/ is compared with directly calculated k/sub H//k/sub D/ (or k/sub H//k/sub T/). Deuterium substitution at the ..beta..-carbon also reduces the contribution of tunneling to ..beta..-carbon isotope effects. Tunneling causes a decrease in the ratio of Arrhenius preexponential factors, A/sub light//A/sub heavy/, not only for primary hydrogen isotope effects but also for secondary hydrogen isotope effects and carbon isotope effects. The ratio increases again when the mass of the transferred atom increases. Deviations from the rule of the geometric mean can be expected when isotopic substitution at one position affects the contribution of tunneling to the isotope effect at another. These predictions provide new experimental tests for tunneling in slow proton transfers. 30 references, 7 tables.

• Research Organization: Univ. of Rochester, NY
• OSTI ID: 5863290
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 107:1; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBON 13
CARBON 14
CARBON ISOTOPES
CHEMICAL REACTIONS
CHLORINATED ALIPHATIC HYDROCARBONS
CORRELATIONS
DATA
DATA ANALYSIS
DEUTERIUM
DEUTERIUM COMPOUNDS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
EXTRAPOLATION
HALOGENATED ALIPHATIC HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROXIDES
INFORMATION
ISOTOPE EFFECTS
ISOTOPES
LABELLED COMPOUNDS
LEAST SQUARE FIT
LIGHT NUCLEI
MATHEMATICAL MODELS
MAXIMUM-LIKELIHOOD FIT
MEDIUM TEMPERATURE
NUCLEI
NUMERICAL DATA
NUMERICAL SOLUTION
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
OXYGEN COMPOUNDS
RADIOISOTOPES
STABLE ISOTOPES
TEMPERATURE DEPENDENCE
THEORETICAL DATA
TRITIUM
TRITIUM COMPOUNDS
YEARS LIVING RADIOISOTOPES