Is an intramolecular hydrogen bond possible in such compounds?
What are the requisites to have intramolecular hydrogen bonding?
As the intramolecular H-bonding is absent in both cases.
In aqueous solution of carbonic acid is a weak acid. It dissociates into its constituent ions as carbonate ions and hydrogen ions. Now, the CO3-2 ion, is stabilized by resonance and produce three equivalent resonating structures.
This makes carbonate ion more stable rather than through intra molecular H-bonding. Now, I already said that carbonic acid is weak acid means all the molecules of carbonic acid are not dissociated. The molecules of carbonic acid which remain undissociated form inter-molecualr H-bonding with each other.
One thing that carbonic acid does not exist via intra-molecular H-bonding because, there is too much ring strain.
In gem-diols there are two -OH groups present on a single carbon. You can get detail reason that why intra-molecular H-bonding is absent in gem-diols.
There is a common example of gem-diol where intra molecular H-bonding is present is chloral hydrate.
Is this possible?
Probably not possible. An elementary explanation would be "too much ring strain."
I'm a bit confused: What are the requisites to occur a intramolecular hydrogen bonding?
5 and 6-membered rings are more favorable. As a matter of fact, beta-ketoacids, when warmed, readily decarboxylate. Why? The intermediate to decarboxylation is stabilized through hydrogen bonding.
Note the 6-membered ring in the picture below.