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Recently I was solving carbonyl compounds and I came across this. Is there some priority order, or logic behind why alcohol reacts first with Grignard reagent and then ketone. Whereas ester could've reacted with 2 moles of RMgX but didn't.

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    $\begingroup$ What is the difference between Grignard reagent reacts with either $\ce{R-OH}$ or $\ce{R-CO-R'}$? There is a pretty good reason for that. $\endgroup$ – Mathew Mahindaratne Jul 10 at 1:05
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    $\begingroup$ so the first one seems like a base so acid-base reaction? And the second one will undergo nucleophilic addition ? so acid-base before substitution . is that it?(●'◡'●) $\endgroup$ – shreya Jul 10 at 1:10
  • $\begingroup$ Looks good but is the structure of R shown? $\endgroup$ – user55119 Jul 10 at 1:13
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    $\begingroup$ @shreya: You are correct, when acidic hydrogen is present it react first such as tin the case of given 1st reaction to give $a$. $\endgroup$ – Mathew Mahindaratne Jul 10 at 6:00
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For the compound given in the question, the priority order of Grignard reagent attack follows,

$\ce{R-OH > R-CO-R' > R-COOR'}$

Reason:

  • Acid-base neutralisation are very fast.

  • Carbonyl carbon is more nucleophilic than carboxylic carbon, as the latter one is stabilized by resonance.


Therefore, first alcohol is attacked and hence P is (a), then the carbonyl part is attacked and hence Q is (b).

Finally, one more mole of RMgX gets used up on the carboxyl part, hence R is not (d).

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