Ahmad IA

Birkby SL

Bullen CA

Groves PD

Lankau T

Lee WH

Maskill H

Menneer ID

Miatt PC

Shaw K

The effect of solvent composition in aqueous ethanol, trifluoroethanol and hexafiuoropropan-2-ol on the rate constant and activation parameters for the uncatalysed hydrolysis of 2-(p-nitrophenoxy)tetrahydropyran (1) was investigated, and the m(TOTs) value is 0.60. This appreciable but less than maximal value is in accordance with an SN1 mechanism with rate-limiting ionization. The α-deuterium secondary kinetic isotope effect (α-kie) for the uncatalysed hydrolysis of 1 is 1.17 in water (46 \ub0C), 1.15 in aqueous trifluoroethanol (50% mole fraction, 70.6 \ub0C) and 1.13 in aqueous ethanol (50% mole fraction, 70.6 \ub0C). These values correspond to about 1.19 at 25 \ub0C, which is characteristic of rate-limiting ionization in an SN1 reaction and appreciably higher than values for enzyme-catalysed glycolysis. The α-kie is smaller under aqueous acidic conditions (1.07, 0.1 mol dm-3 hydrochloric acid, 20.2 \ub0C) when 1 hydrolyses with acid catalysis. The previously reported α-kie for the hydrolysis of 1 in buffered aqueous dioxan (1.063, 25 \ub0C) is now seen to correspond to acid-catalysed hydrolysis. These new results for 1 indicate that transition structures in enzyme-catalysed glycolyses with α-kie values of less than about 1.15 at 25 \ub0C involve a lower degree of carbenium ion character than has hitherto been assumed. Copyright \ua9 2004 John Wiley &amp; Sons, Ltd

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Hydrolysis of 2-(p-nitrophenoxy)tetrahydropyran: Solvent and α-deuterium secondary kinetic isotope effects and relationships with the solvolysis of simple secondary alkyl arenesulfonates and the enzyme-catalyzed hydrolysis of glycosides

Hydrolysis of 2-(p-nitrophenoxy)tetrahydropyran: Solvent and α-deuterium secondary kinetic isotope effects and relationships with the solvolysis of simple secondary alkyl arenesulfonates and the enzyme-catalyzed hydrolysis of glycosides

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