Heavy atom isotope effect studies of elimination reaction mechanisms. 1. A kinetic and carbon-14 kinetic isotope effect study of the base-promoted dehydrochlorination of substituted 1-phenylethyl-2-/sup 14/C chlorides

Journal Article · Wed Jun 15 04:00:00 EDT 1983 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00350a038· OSTI ID:5708433

Hasan, T; Sims, L B; Fry, A

Upon treatment with the solvent conjugate base, the primary reaction of substituted 1-phenylethyl chlorides is elimination to substituted styrenes in tert-butanol (t-BuOH)-10% v/v dimethyl sulfoxide (Me/sub 2/SO) at 60/sup 0/C and in bis(2-hydroxyethyl) ether-10% v/v Me/sub 2/SO at 45/sup 0/C. Kinetic studies using eight substituted chlorides show that these reactions are strongly accelerated by both electron-donating and electron-withdrawing substituents, probably indicating a fairly reactant-like E2 transition state with the mechanism changing from El-like E2 to ElcB-like E2 as the substituents change from electron donating group (EDG) to electron withdrawing (EWG). In this first carbon isotope effect study of an elimination reaction of an alkyl chloride, carbon-14 kinetic isotope effects have been measured in the alkoxide/bis(2-hydroxyethyl) ether-Me/sub 2/SO system for 1-(4-methylphenyl)ethyl-2-/sup 14/C chloride, k/sup ..beta../k = 1.038, 1-phenylethyl-2-/sup 14/C chloride, k/sup ..beta../k = 1.058, and 1-(4-chlorophenyl)ethyl-2-/sup 14/C chloride, k/sup ..beta../k = 1.068. Clearly none of these compounds reacts by an irreversible El mechanism, for which no ..beta..-carbon isotope effect should be observed. The trend in the results is what would be expected from increased C/sub ..beta../-H bond rupture as the E2 transition state shifts from El-like to ElcB-like. Theoretical calculations involving El-like E2 transition-state models show that in this region only for a reaction coordinate motion tht strongly couples C/sub ..beta../-H bond rupture, C/sub ..cap alpha../-C/sub ..beta../ double bond formation, and C/sub ..cap alpha../-Cl bond rupture does the calculated value for k/sup ..beta../k come into the experimentally observed range, and then only for reactant-like models. 2 figures, 5 tables.

• Research Organization: Univ. of Arkansas, Fayetteville
• OSTI ID: 5708433
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 105:12; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ALCOHOLS
AROMATICS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BUTANOLS
CALCULATION METHODS
CARBON 14
CARBON ISOTOPES
CHEMICAL REACTION KINETICS
CHLORINATED AROMATIC HYDROCARBONS
CHROMATOGRAPHY
DATA
DMSO
ETHERS
EVEN-EVEN NUCLEI
EXPERIMENTAL DATA
GAS CHROMATOGRAPHY
HALOGENATED AROMATIC HYDROCARBONS
HYDROXY COMPOUNDS
INFORMATION
ISOTOPE APPLICATIONS
ISOTOPE EFFECTS
ISOTOPES
ISOTOPIC EXCHANGE
KINETICS
LABELLING
LIGHT NUCLEI
NUCLEI
NUMERICAL DATA
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC SOLVENTS
ORGANIC SULFUR COMPOUNDS
RADIOISOTOPES
REACTION KINETICS
SAMPLE PREPARATION
SEPARATION PROCESSES
SOLVENTS
SULFOXIDES
TRACER TECHNIQUES
YEARS LIVING RADIOISOTOPES