Secondary .alpha.-deuterium kinetic isotope effects and transition-state structures for the hydrolysis and hydrazinolysis reactions of formate esters

1975 ◽  
Vol 97 (15) ◽  
pp. 4317-4322 ◽  
Author(s):  
Zayn Bilkadi ◽  
Robert De Lorimier ◽  
Jack F. Kirsch
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Transition State Structures

SECONDARY KINETIC ISOTOPE EFFECTS IN THE SOLVOLYSES OF 2-(2,4-DIMETIIOXYPHENYL)-1,1-d2-ETHYL AND 2-(3,5-DIMETHOXYPHENYL)-1,1-d2-ETIIYL p-BROMOBENZENESULFONATES

1966 ◽  
Vol 44 (21) ◽  
pp. 2491-2495
Author(s):  
C. C. Lee ◽  
L. Noszkó
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Ion Pair ◽  
Similar Data ◽  
Kinetic Isotope ◽  
Ion Stability ◽  
Transition State Structures

The secondary α-deuterium kinetic isotope effects in the acetolyses and formolyses of 2-(2,4-dimethoxyphenyl)-ethyl and 2-(3,5-dimethoxyphenyl)-ethyl p-bromobenzenesulfonates (I-OBs and II-OBs, respectively) and their corresponding 1,1-dideuterio analogues (I-OBs-1-d2 and II-OBs-1-d2) were determined. The observed kH/kD values are compared with similar data from the literature for 2-phenylethyl and 2-p-anisylethyl p-toluenesulfonates (III-OTs and IV-OTs, respectively). In the formolyses of III-OTs, IV-OTs, and I-OBs, which proceed either chiefly or exclusively by way of bridged ions as intermediates, the isotope effects appear to increase slightly with increasing bridged-ion stability. For I-OBs and I-OBs-1-d2, acetolyses gave smaller kH/kD values than formolyses because of deuterium scrambling caused by ion-pair returns during the acetolysis. Acetolyses and formolyses of II-OBs and II-OBs-1-d2 gave lower isotope effects than the corresponding reactions with I-OBs and I-OBs-1-d2. The magnitudes of the observed isotope effects in relation to transition-state structures are discussed.

Transition state structures in glycosidase catalysis: kinetic isotope effects and structure-reactivity parameters

1988 ◽  
Vol 47 (2-3) ◽  
pp. 255-263 ◽  
Author(s):  
A.C. Elliott ◽  
B.F. Li ◽  
C.A.J. Morton ◽  
J.D. Pownall ◽  
T. Selwood ◽  
...  
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Transition State Structures

Kinetic isotope effects as guides to transition-state structures in deprotonation reactions

1971 ◽  
Vol 93 (2) ◽  
pp. 512-514 ◽  
Author(s):  
Frederick G. Bordwell ◽  
William J. Boyle
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Transition State Structures

The Importance of Anharmonicity of The Vibrational Excited States in Chemical Kinetics

1975 ◽  
Vol 53 (20) ◽  
pp. 3069-3074 ◽  
Author(s):  
Jan Bron
Keyword(s):  
Transition State ◽  
Excited States ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Vibrational States ◽  
Vibrational Anharmonicity ◽  
Kinetic Isotope ◽  
Large Correction ◽  
Lower Temperature ◽  
Lower Temperature Region

The corrections to rate constants for an harmonicity of vibrational excited states have been evaluated over the temperature range of 200–1100 K. The reaction O2 + X, where X is H or D, has been chosen as the model system. Only the influence of vibrational anharmonicity of the triatomic transition state has been determined. Two geometric shapes for the transition state, bent and isosceles configurations, have been investigated in detail by the bond order method.It is found that the correction can be large, depending upon the geometry and force field of the transition state and the temperature. The magnitude of the correction for anharmonicity of the vibrational excited states depends mainly, at a particular temperature, on the strength of the O—X bond in the transition state. In the case of a large correction, anharmonicity may lead to a nonlinear Arrhenius plot.Because of cancellation effects, the correction for anharmonicity of the excited vibrational states in kinetic isotope effects can be ignored in the lower temperature region. It has also been found that anharmonicity of the vibrational groundstate can explain unexpected large isotope effects.

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