The Effects of Deuterium Substitution on the Rates of Organic Reactions. VI. Secondary Isotope Effects on the Solvolysis Rates of γ-Methyl Substituted t-Alkyl Chlorides1

1961 ◽  
Vol 83 (1) ◽  
pp. 240-243 ◽  
Author(s):  
V. J. Shiner
Keyword(s):  
Isotope Effects ◽  
Organic Reactions ◽  
Deuterium Substitution

ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: II. DEUTERO STYRENES AND RING-SUBSTITUTED STYRENES

1965 ◽  
Vol 43 (10) ◽  
pp. 2737-2743 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Peroxy Radical ◽  
Propagation Rate ◽  
Chain Termination ◽  
Absolute Rate ◽  
First Order ◽  
Oxidation Rates ◽  
Deuterium Substitution ◽  
Termination Process

The effect of deuterium substitution on the absolute rate constants for the bimolecular chain termination process in the oxidation of styrene indicates that the α-hydrogen is abstracted in this reaction. The first order chain termination process is suppressed both by deuteration of styrene at the α-position and by the addition of heavy water. A possible mechanism for this termination is proposed. There appear to be small secondary deuterium isotope effects in the propagation reaction.The overall oxidation rates and the propagation rate constants are increased by the addition to the aromatic ring of both electron-attracting and electron-releasing substituents. This is attributed in the former case to the increased stability of the resulting styryl radicals and in the latter case to the increased stability of a dipolar transition state. In hydrogen atom abstraction from 2,6-di-t-butyl-4-methylphenol, the peroxy radical from 3-chlorostyrene is more reactive than that from styrene which, in turn, is more reactive than the peroxy radical from 4-methoxy-styrene.

SECONDARY KINETIC ISOTOPE EFFECTS IN BIMOLECULAR NUCLEOPHILIC SUBSTITUTIONS: II. α-DEUTERIUM EFFECTS IN MENSCHUTKIN REACTIONS OF METHYL IODIDE

1965 ◽  
Vol 43 (1) ◽  
pp. 40-46 ◽  
Author(s):  
K. T. Leffek ◽  
J. W. MacLean
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Systematic Change ◽  
Tertiary Amines ◽  
Nucleophilic Substitutions ◽  
Methyl Group ◽  
Kinetic Isotope ◽  
Deuterium Substitution ◽  
Different Temperatures ◽  
Rate Ratios

Secondary deuterium isotope effects have been measured for the reactions between methyl and methyl-d3 iodides and a series of tertiary amines in benzene solvent. Deuterium substitution increased the rate of each reaction but the rate ratios (kH/kD) show no systematic change with variation in the structure of the amine. The isotope effect for the reaction with 2-picoline was measured at different temperatures over a range of 40 deg and shows no change. These isotope effects may be rationalized as internal rotational effects of the methyl group or as solvation effects.

Sterically Hindered Aromatic Compounds. V. Solvolysis of p-Methyl-, 2,4,6-Trimethyl-, and 2,4,6-Tri-t-butylbenzyl Chloride. Effect of Solvent and α-Deuterium Substitution

1972 ◽  
Vol 50 (24) ◽  
pp. 3965-3972 ◽  
Author(s):  
L. R. C. Barclay ◽  
J. R. Mercer ◽  
J. C. Hudson
Keyword(s):  
Chemical Shifts ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Butyl Alcohol ◽  
Deuterium Isotope Effect ◽  
Limiting Behavior ◽  
Kinetic Isotope ◽  
Deuterium Substitution ◽  
Alcohol Water ◽  
Chloride Effect

Rates, activation parameters, and kinetic α-deuterium isotope effects are reported for solvolysis of p-methyl-benzyl chloride in 80% trifluoroethanol–water, and in ethanol–water and t-butyl alcohol–water of varying solvent compositions. The α-deuterium isotope effect in trifluoroethanol–water (kH/kD = 1.14 per D) indicates approximately limiting behavior. Results in the other solvents (kH/kD = 1.04–1.08) indicate considerable nucleophilic participation by solvent in the transition state. 2,4,6-Trimethylbenzyl chloride gave kH/kD = 1.09 in 80% ethanol–water but kH/kD = 1.16 in 80% trifluoroethanol–water. 2,4,6-Tri-t-butylbenzyl chloride showed kH/kD effects of 1.13–1.15 in t-butyl alcohol–water and 1.15–1.16 in ethanol–water. The higher kinetic isotope effects for solvolysis of these trialkylbenzyl chlorides are discussed in terms of steric hindrance to nucleophilic participation by solvent. N.m.r. chemical shifts give evidence for steric compression of the benzylic protons in 2,4,6-tri-t-butylbenzyl chlorides.

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