Grignard reagents add to the carbonyl – irreversibly. Hydroxide can add to the carbonyl to form a hemiacetal but it is reversible, and eventually deprotonation occurs to give the enolate.
With Grignards, deprotonation at the alpha position only tends to occur when there is a lot of steric bulk around the carbonyl carbon. The C-H bond has to be oriented at 90° in order for deprotonation to occur, otherwise the resulting carbanion won’t be in resonance with the carbonyl pi bond

Thank you James for your reply!

I purchased the summary, and realized I wasn’t ready for summary yet, and going through the posts now, and it’s really helpful. I just thought it will be really good if you can put together these post contents into printable pdf. I would definitely pay a reasonable price to have this contents easier to read, carry, and make notes..!

Any time you form a carbocation, watch out for rearrangements.

Hi, if you deprotonate C-H adjacent to a ketone, the carbon will not be sp3 hybridized for long. It is energetically favourable for the carbon to re-hybridize to sp2, which puts the lone pair in a p orbital and can then be conjugated with the p orbitals in the C=O group.

It’s this atomic motion which makes deprotonation of C-H “slow”.