# Priority order of attack of grignard reagents on functional groups

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.

• 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. Jul 10 '20 at 1:05
• 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?(●'◡'●) Jul 10 '20 at 1:10
• Looks good but is the structure of R shown? Jul 10 '20 at 1:13
• @shreya: You are correct, when acidic hydrogen is present it react first such as tin the case of given 1st reaction to give $a$. Jul 10 '20 at 6:00

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).