Role of solvent in the mechanism of amine oxide thermolysis elucidated by the temperature dependence of a kinetic isotope effect

1981 ◽  
Vol 103 (15) ◽  
pp. 4650-4652 ◽  
Author(s):  
Harold Kwart ◽  
Martin Brechbiel
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Amine Oxide ◽  
Kinetic Isotope ◽  
Role Of Solvent

Kinetic Isotope Effect Studies on the Reaction of Benzyl Nitrate with Base in Varions Solvents

1971 ◽  
Vol 49 (23) ◽  
pp. 3856-3865 ◽  
Author(s):  
Carol A. Pollock ◽  
P. J. Smith
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Nitrogen Isotope ◽  
Minor Role ◽  
Solvent Mixtures ◽  
Elimination Reaction ◽  
Kinetic Isotope ◽  
Role Of Solvent

The role of solvent and base on the nature of the transition state for the concerted one-step carbonyl elimination reaction of benzyl nitrate has been examined using rate and kinetic isotope effect techniques. The primary hydrogen–deuterium isotope effect was found to increase with increasing strength of the abstracting base, kH/kD = 5.94 and 6.41 at 30° for reaction with EtO−/EtOH and t-BuO−/t-BuOH, respectively. The nitrogen isotope effect decreased with increasing strength of the abstracting base, 2.07, 1.82, and 1.54% for reaction with OH−/40 vol % EtOH–H2O, EtO−/EtOH, and t-BuO−/t-BuOH, respectively. The conclusion is reached that an increase in the strength of the abstracting base leads to a more reactant-like transition state with decreased rupture of both the C—H and O—N bonds. The role of solvent on the nature of the transition state was examined by determining rates and nitrogen isotope effects for reaction in various ethanol–water and ethanol–dimethyl sulfoxide mixtures. The nitrogen effect was found to remain essentially constant in solvent mixtures ranging from 65 vol % EtOH–H2O on the one hand to 80 vol% EtOH–DMSO on the other hand where the rate constants differed by a factor of 100 fold. It is concluded that solvent plays only a very minor role in determining transition state structure for the concerted elimination reaction of a neutral substrate with base.

Quantum Mechanical Tunneling in Homodienyl Sigmatropic [1,5]-Hydrogen Shifts of (Hydroxymethyl)styrylcyclopropanes

1990 ◽  
Vol 43 (6) ◽  
pp. 1071 ◽  
Author(s):  
GG Pegg ◽  
GV Meehan
Keyword(s):  
Low Temperature ◽  
Temperature Dependence ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Natural Compounds ◽  
Quantum Mechanical ◽  
Strong Temperature Dependence ◽  
Quantum Mechanical Tunneling ◽  
Hydrogen Migration ◽  
Kinetic Isotope

The strong temperature dependence of the deuterium kinetic isotope effect observed for homodienyl [1,5]-hydrogen migration of [hydroxy (D)methyl] styrylcyclopropanes (1c,d) in hexane solvent is suggestive of a significant tunnelling contribution to the mechanism. While the hydroxy substituent at the migration origin appears to influence the thermolytic behaviour of these molecules, attempts to promote oxy anionic homodienyl rearrangement in the isotopically natural compounds (1a,b) at low temperature were unsuccessful.

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