[furaniki18]

what would be the major product for the following reactions?
i know that grignard reagent can act as a base as well as a nucleophile but what will it act as in the above reactions i.e. will it accept a proton from the -OH group attached to the benzene ring and thus form methane or will it favour the nucleophilic attack on the carbonyl group? and also in the second question if it favours nucleophilic attack wouldn't it attack the aldehyde group rather than ketone because the aldehyde group will not be sterically hindered?

[Dan]

Grignard reagents are instantaneously destroyed in water, because they are so basic they immediately deprotonate water. The stronger the acid, the more rapid the acid-base reaction will be.

So, how do you think a phenol will compare to water in terms of acid-base chemistry?

[furaniki18]

phenol is definitely a stronger acid than water...but exactly what i want to ask is that is the basic character of grignard stronger than its nucleophilic character or otherwise? i am guessing this is something hard to decide and something like this will be most likely determined by the chemistry of the substrate..i am looking for that exact hint to decide whether the substrates in the above questions would prefer the attack of grignard as a base or grignard as a nucleophile...
 

[Dan]

I would expect mostly acid-base reaction. If you only use 1 eq of Grignard you might get a bit of the addition products, but probably not much. Most of it will be destroyed by protonation before it reacts with the carbonyls.

[fledarmus]

Acid-base reactions are generally the fastest reactions you will see. If it is possible for an acid-base reaction to occur, it will generally happen first, and if there is a large difference in pKa's it will be essentially complete. Grignard reagents are very strong bases and phenols are fair acids - the Grignard will be protonated very rapidly, and if you only use one equivalent, you won't see any addition.

If you use two equivalents of a Grignard, you can sometimes still get the reaction to occur even on the deprotonated compound - Grignard reagents are also good nucleophiles.