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enter image description here1,4-Benzoquinone, commonly known as para-quinone, is a chemical compound with the formula $\ce{C6H4O2}$

When there are alpha Hydrogen's why can't it show tautomerism?

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    $\begingroup$ Look at the supposed tautomer. $\endgroup$ – aventurin Jan 27 '18 at 14:48
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You could sort of devise a tautomer by transferring an $\alpha$ hydrogen from carbon to oxygen. But if you draw the resulting structure you find a pair of cumulated double bonds. That tends to be unstable, and since the cumulated double-bonded carbons favor a 180° bond angle putting them into a relatively small ring makes them a lot more unstable. Your proposed tautomer is way out there in energy.

Tautomerization of a ketone works better when you have an $\alpha$ hydrogen on a saturated carbon atom.

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    $\begingroup$ Thankyou, that drives the reasoning straight to my heart. @Oscar Lanzi $\endgroup$ – user27533 Jan 27 '18 at 19:04

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