Question

How is Carbonyl group converted into above compound?

$-\underset{OH}{\underset{|}{\stackrel{|}{C}}}-\underset{OH}{\underset{|}{\stackrel{|}{C}}}-$

Answer 1

Oxidattion of Aldehydes and Ketones gives carboxylic acids which on addition of water to an aldehydes or ketone gives a hydrated or diol product, i.e., next oxidation level as shown above.