In this step neutral starting materials turn into

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Unformatted text preview: rial more. The energy gap will increase and the reaction go more slowly. The third reaction is different as it has more than one step. It is a carbonyl substitution of the kind we met in chapter 10. The nucleophile Solutions for Chapter 12 – Equilibria, Rates and Mechanisms (ammonia) attacks the carbonyl group to form a tetrahedral intermediate that decomposes with the loss of the better leaving group. O R O NH3 R OMe NH3 fast OMe HO OH NH2 R R OMe O fast NH2 R NH2 We have marked two steps ‘fast’ because they are just proton transfers between nitrogen and oxygen atoms. Either of the other two steps might be rate determining. In this substitution the leaving group is relatively good (compare problem 2) and the rate- determining step is the first: the usual one for carbonyl substitutions. In this step, neutral starting materials turn into charged (zwitterionic) intermediate so the transition state is becoming charged and the reacti...
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