| Abstract
| - Kinetic isotope effects were measured for the acyl transferreaction from p-nitrophenyl acetate tohydroxylamine at pH 6.0 and 12.0. The isotope effects measured andtheir values at pH 6.0 and 12.0, respectively,are as follows: leaving group oxygen-18 isotope effect, 1.0310 and1.0074; the carbonyl oxygen-18 isotope effect,1.0082 and 1.0008; the β-deuterium isotope effect, 0.9644 and 0.9516;the carbonyl carbon-13 isotope effect, 1.0287and 1.0337; the nitro group nitrogen-15 isotope effect, 1.0009 and1.0011. The solvent deuterium isotope effect is1.4 at pH 7.5 and 0.85 at pH 12.0. The leaving group oxygen-18isotope effect was measured as a function of pHbetween 6.0 and 12.0 and was found to have an inflection at pH 10.0between the plateau regions at high and lowpH. The results are consistent with rate limiting breakdown of anintermediate for the low pH reaction and attackof hydroxylamine anion with concerted expulsion of nitrophenolate ionat high pH.
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