I was given a question of pinacol pinacolon rearrangement of butan-2,3-diol where the methyl groups were anti to the respective hydroxy groups. Can the C2-C3 bond be rotated to allow hydrogen to be anti to the leaving hydroxy group, but I have heard that mechanism of this rearrangement is concerted. Therefore I can't decide the major product.

  • $\begingroup$ Yes,it can be, as in this configuration, the antibonding sigma orbital of the leaving group will be parallel to the lone pairs of the other hydroxyl group $\endgroup$ – Yusuf Hasan Apr 11 '20 at 7:55
  • $\begingroup$ Sorry, I didn't quite understand how this will lead to bond rotation. Can you explain a little more? $\endgroup$ – B.Anshuman Apr 11 '20 at 8:24

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