Secondary .beta.-deuterium isotope effects in decarboxylation and elimination reactions of .alpha.-lactylthiamin: intrinsic isotope effects of pyruvate decarboxylase

1986 ◽  
Vol 108 (24) ◽  
pp. 7828-7832 ◽  
Author(s):  
Ronald. Kluger ◽  
Michael. Brandl
Keyword(s):  
Isotope Effects ◽  
Pyruvate Decarboxylase ◽  
Deuterium Isotope Effects ◽  
Elimination Reactions

Kinetics and isotope effects of the β-elimination reactions of some 2,2-di(4-nitrophenyl)chloroethanes promoted by tetramethylguanidine in aprotic solvents

1985 ◽  
Vol 63 (6) ◽  
pp. 1194-1197 ◽  
Author(s):  
Arnold Jarczewski ◽  
Malgorzata Waligorska ◽  
Kenneth T. Leffek
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Aprotic Solvents ◽  
Polar Solvents ◽  
Deuterium Isotope Effects ◽  
Elimination Reactions

Rate constants for the β-elimination of HCl from 2,2-di(4-nitrophenyl)-1,1-dichloroethane (I) and 2,2-di(4-nitrophenyl)-1,1,1-trichloroéthane (II) promoted by tetramethylguanidine in the aprotic solvents acetonitrile, tetrahydrofuran, and n-hexane have been measured. The activation parameters are characterized by small enthalpies of activation (4.1 to 7.3 kcal mol−1) and large negative entropies of activation (−35 to −50 cal mol−1 deg−1). The primary deuterium isotope effects at 20° C range from kH/kD = 4.8 to 10.3. The results are interpreted to indicate an (EcB)1 mechanism for both substrates I and II in acetonitrile solvent and an E2H or mixed (ElcB)1–E2H mechanism in the less polar solvents, tetrahydrofuran and n-hexane.

ISOTOPE EFFECT STUDIES ON ELIMINATION REACTIONS: III. NITROGEN ISOTOPE EFFECTS IN THE E2 REACTION OF ETHYLTRIMETHYL-AMMONIUM AND 2-PHENYLETHYLTRIMETHYLAMMONIUM IONS

1963 ◽  
Vol 41 (7) ◽  
pp. 1759-1767 ◽  
Author(s):  
G. Ayrey ◽  
A. N. Bourns ◽  
V. A. Vyas
Keyword(s):  
Isotope Effect ◽  
Quaternary Ammonium ◽  
Isotope Effects ◽  
Transition States ◽  
Nitrogen Isotope ◽  
Quaternary Ammonium Salts ◽  
Ammonium Salts ◽  
Relative Extent ◽  
Deuterium Isotope Effects ◽  
Elimination Reactions

Nitrogen isotope effects have been determined for the E2 reaction of two quaternary ammonium salts with ethoxide ion in ethanol. Ethyltrimethylammonium iodide gave k14/k15 values of 1.017 at 60° and 1.015 at 95°, while 2-phenylethyltrimethylammonium bromide gave 1.012 at 40° and 1.009 at 60°. These results and the β-deuterium isotope effects reported by others have been interpreted in terms of the relative extent of Cα—N+ and Cβ—H bond weakening in the transition states of the two reactions.

Sign in / Sign up

Export Citation Format

Share Document