What are the orders of rates of oxidation with $\ce{HIO4}$ of the following diols? Explain with reasons.

(a) $\ce{Me2C(OH)C(OH)Me2}$
(b) $\ce{Me2C(OH)CH(OH)Me}$
(c) $\ce{CH2(OH)CH2(OH)}$
(d) $\ce{MeCH(OH)CH(OH)Me}$

I know that the reaction proceeds by forming a cyclic diester of periodic acid followed by cleavage of $\ce{C-C}$ bond and formation of $\ce{C=O}$ bond. But how do we compare the rates of the given compounds?

My first thought was to think $\ce{C-C}$ cleavage as formation of a pseudo carbocation which would be stabilised by +I effect of the alkyl groups and also the hyperconjugation, but I don't think it is right.

  • $\begingroup$ Could it possibly be related to stearic hinderance for the ring to form? $\endgroup$ Commented Mar 19, 2019 at 9:21
  • $\begingroup$ Could be but I am not sure $\endgroup$ Commented Mar 19, 2019 at 10:22
  • $\begingroup$ @SidharthGiri and Aditya One thing which you can be assured is that,whatever the differentiating factor is,it will certainly be before the formation of thr cyclic intermediate as after that,it is a pericyclic intramolecular rearrangement which is pretty easy to be done in all the cases with minimum requirement of any activation energy.. $\endgroup$ Commented Mar 19, 2019 at 10:39
  • $\begingroup$ Also.. Is the answer a>b>d>c? $\endgroup$ Commented Mar 19, 2019 at 11:10
  • $\begingroup$ I don't have the answers and that is also a big problem $\endgroup$ Commented Mar 19, 2019 at 13:04


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