A compound having formula $\ce{C9H7O2Cl}$ (O = oxygen) exists predominantly in enol form (A) and also in keto form (B). On oxidation with $\ce{KMnO4}$ it gives m-chlorobenzoic acid as one of the products. Identify (A) and (B).

(subjective question; no options were given)

I tried it and found the double bond equivalent as 6, 4 of which were utilized in benzene ring. Also, the benzylic carbon must have at least one hydrogen. Therefore I determined the following structure as (A):

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But my book suggests (A) should be:

enter image description here

Please explain whether both are correct or only one product will exist.

Source: Joint Entrance Exam (JEE) 2003 India


Both the answers are correct but the most appropriate will be B as the chelation occurs because of hydrogen bonding which makes it more stable. H-bonding is possible in your structure but the ring is less stable .Less stable chelate ring is formed than the other.

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  • $\begingroup$ But there will also be H bonding i product 1 $\endgroup$ – Anirudh May 8 '18 at 13:20
  • $\begingroup$ In your case the ring will be 5 membered which is less stable than 6 membered ring $\endgroup$ – Aman Chande May 8 '18 at 13:54
  • $\begingroup$ Where is there a 5-membered ring? $\endgroup$ – pentavalentcarbon May 8 '18 at 14:14
  • $\begingroup$ What do you mean by 5 membered ring $\endgroup$ – Anirudh May 8 '18 at 14:40
  • $\begingroup$ There is no actual ring there $\endgroup$ – Anirudh May 8 '18 at 14:41

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