Use of kinetic isotope effects in mechanism studies. 3. Measurement of hydrogen isotope effects on the primary chlorine isotope effect during elimination reactions

1980 ◽  
Vol 102 (27) ◽  
pp. 7955-7956 ◽  
Author(s):  
H. F. Koch ◽  
J. G. Koch ◽  
W. Tumas ◽  
D. J. McLennan ◽  
B. Dobson ◽  
...  
Keyword(s):  
Isotope Effect ◽  
Hydrogen Isotope ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Chlorine Isotope ◽  
Kinetic Isotope ◽  
Elimination Reactions

SOME DEUTERIUM KINETIC ISOTOPE EFFECTS: IV. β-DEUTERIUM EFFECTS IN WATER SOLVOLYSIS OF ETHYL, ISOPROPYL, AND tert-BUTYL COMPOUNDS

1960 ◽  
Vol 38 (11) ◽  
pp. 2171-2177 ◽  
Author(s):  
K. T. Leffek ◽  
J. A. Llewellyn ◽  
R. E. Robertson
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Alkyl Halides ◽  
Tert Butyl ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
Intramolecular Forces

The secondary β-deuterium isotope effects have been measured in the water solvolytic reaction of alkyl halides and sulphonates for primary, secondary, and tertiary species. In every case the kinetic isotope effect was greater than unity (kH/kD > 1). This isotope effect may be associated with varying degrees of hyperconjugation or altered non-bonding intramolecular forces. The experiments make it difficult to decide which effect is most important.

Solvolysis of specifically deuterated 7-chloro- and 7-bromo-exo-2-norbornyl brosylates; unusually large γ-kinetic isotope effects in the absence of σ-participation

1980 ◽  
Vol 58 (16) ◽  
pp. 1738-1750 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
George Timmins ◽  
Frank Peter Cappelli
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope

A series of specifically deuterated syn-7-chloro-, anti-7-chloro-, syn-7-bromo-, and anti-7-bromo-exo-2-norbornyl brosylates have been prepared and solvolyzed in NaOAc-buffered 80:20 EtOH–H2O. For solvolysis at 25 °C the γ-kinetic isotope effects (KIE's) for syn-7-chloro-exo-2-norbornyl brosylate-endo-6-d (1e), anti-7-chloro-exo-2-norbornyl brosylate-endo-6-d (2c), syn-7-bromo-exo-2-norbornyl brosylate-endo-6-d (1f), anti-7-bromo-exo-2-norbornyl brosylate-endo-6-d (2d), syn-7-chloro-exo-2-norbornyl brosylate-exo,exo-5,6-d2 (1g), anti-7-chloro-exo-2-norbornyl brosylate-exo,exo-5,6-d2 (2e) are 1.125 ± 0.007, 1.128 ± 0.005, 1.063 ± 0.008, 1.149 ± 0.020, 1.119 ± 0.011, and 1.115 ± 0.013, respectively. There is no detectable γ-kinetic isotope effect for solvolysis of anti-7-chloro-endo-2-norbornyl brosylate-endo-6-d(3a) and the β-KIE for anti-7-chloro-exo-2-norbornyl brosylate-exo-3-d(4a) is 1.111 ± 0.011. From a consideration of the possible sources of the unusually large secondary KIE's, we conclude that the exo-6-d and endo-6-d γ-KIE's likely are derived from a combination of effects rather than from participation of the C1—C6 bond in the ionization step.

Kinetic hydrogen isotope effects in the ionization of some carbon acids

1970 ◽  
Vol 318 (1535) ◽  
pp. 421-440 ◽  
Keyword(s):  
Aqueous Solutions ◽  
Rate Constants ◽  
Hydrogen Isotope ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Pyridine Bases ◽  
Carbon Acids ◽  
Ethyl Nitroacetate ◽  
Basic Strength

Rate constants in aqueous solutions are reported for proton and deuteron abstraction by a variety of bases from tricarbomethoxymethane, the propan-2-one-1-sulphonate ion, 2-acetylcyclohexanone and ethyl nitroacetate. The rates of ionization were measured by using bromine or iodine as scavengers to remove the anions, and, for ethyl nitroacetate by direct observation of the rate of appearance of the anion. The kinetic isotope effects vary from k H / k D = 2.5 to k H / k D = 10.3, and confirm the regularities previously found (Bell & Crooks 1965; Bell & Goodall 1966). In particular, the results for the reaction of ethyl nitro-acetate with nine bases show clearly that with increasing basic strength the isotope effect passes through a well-marked maximum. Sterically hindered pyridine bases give rise to abnormally high isotope effects, probably attributable to increased tunnel corrections.

scholarly journals Isotope effect analyses provide evidence for an altered transition state for RNA 2′-O-transphosphorylation catalyzed by Zn2+

2016 ◽  
Vol 52 (24) ◽  
pp. 4462-4465 ◽  
Author(s):  
Shuming Zhang ◽  
Hong Gu ◽  
Haoyuan Chen ◽  
Emily Strong ◽  
Edward W. Ollie ◽  
...  
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Base Catalysis ◽  
Kinetic Isotope

Solvent D2O and18O kinetic isotope effects on RNA 2′-O-transphosphorylation catalyzed by Zn2+demonstrate an altered transition state relative to specific base catalysis.

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