[Quietus]

Hello! I feel like I understand this stuff pretty well the way our professor teaches in lecture, but sometimes the lab questions ask us stuff that I don't feel comfortable with. I suppose that's normal. Anyway:

Q: Give the reaction scheme, showing products formed (before hydrolysis) when one equiv. of ethylmagnesium bromide is treated with one equiv. of 5-hydroxy-2-pentanone. Does addition of two equivalents of the Grignard reagent to this ketone yield a different product(s)? If so, give the structures.

My answer: Simple, the grignard reagent creates a CH3CH2 carbanion that attacks at the base of the carbonyl group. It produces 3-methyl-1,6 hexadiol. In my experience with these questions the "if so" parts are invariably true, but since it's not an ester and the ketone can't recreate itself, there should be no reaction with the second grignard equivalent, right?

Please tell me if I'm wrong

[gfunk]

You're right in that Grignard reagents attack carbonyl carbons.  However, look at the other functional group: the hydroxyl.  Grignard reagents are carbon nucleophiles and are essentially a C- species.  Thus, Grignard reagents are also strong bases, and any proton that is even a bit acidic will be deprotonated.  Adding one equivalent will deprotonate the hydroxyl group, while the second equivalent will perform the nucleophilic attack.

Adding two equivalents of the Grignard reagent when such situations arise and an attack on a carbonyl is desired is quite commonplace.

Hope that helps!

Edit: Oh, and good job recognising the difference between ketones and esters.

[Quietus]

Aha! I knew that. Sometimes it's hard to pull all those little bits of information together when you need them.

I wasn't thinking clearly when I drew the picture of the product, so I misnamed it as well. I think the real product would be 4-methyl-1,4-hexadiol.

Thanks for the *delete me*