Secondary deuterium isotope effects and the conformation of transition states in the solvolyses of 3.alpha.- and 3.beta.-cholestanyl brosylates

1975 ◽  
Vol 40 (20) ◽  
pp. 2949-2953 ◽  
Author(s):  
Marko Tarle ◽  
Stanko Borcic ◽  
D. E. Sunko
Keyword(s):  
Isotope Effects ◽  
Transition States ◽  
Deuterium Isotope Effects

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.

Mechanism of hydration and isomerisation of 4-ethylidene-2,6-di-tert-butyl-2,5-cyclohexadien-1-one. Kinetics, acid-base catalysis and solvent deuterium isotope effects

1979 ◽  
Vol 44 (1) ◽  
pp. 110-122 ◽  
Author(s):  
Jiří Velek ◽  
Bohumír Koutek ◽  
Milan Souček
Keyword(s):  
Aqueous Medium ◽  
Rate Equation ◽  
Kinetic Data ◽  
Isotope Effects ◽  
Base Catalysis ◽  
Quinone Methide ◽  
Reaction Products ◽  
Acid Base ◽  
Deuterium Isotope Effects ◽  
Hydroxybenzyl Alcohol

Competitive hydration and isomerisation of the quinone methide I at 25 °C in an aqueous medium in the region of pH 2.4-13.0 was studied spectrophotometrically. The only reaction products in the studied range of pH are 4-hydroxybenzyl alcohol (II) and 4-hydroxystyrene (III). The form of the overall rate equation corresponds to a general acid-base catalysis. The mechanism of both reactions for three markedly separated pH regions is discussed on the basis of kinetic data and solvent deuterium effect.

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