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We describe an exercise for training students in chemical kinetics that involves the oxidation of polyols with potassium dichromate. The reactivities of the different polyols are compared and differences are interpreted in terms of stereoelectronic factors. In each case, the relative value of the experimental rate constant is used to infer the role of the substituents in the reaction pathway.
The proposed exercise combines an experimental part (the measurement of the rate constants) and discussion of the experimental results in terms of factors responsible for the observed differences. The reactivity trends observed for the CrVI oxidation reaction are ascribed to (i) the role of the substituent on the reactivity of diols, (ii) the role of the C-3 and C-4 configuration on the reactivity of aldohexoses, and (iii) the role of the C-2 substituent on the reactivity of aldohexoses. Arguments are given to explain each of these.
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