Acetals can serve as protecting groups for 1,2-diols,as well as for aldehydes and ketones. When the acetal is formed from acetone plus the diol, the acetal is called as acetonide. Show the acetonides formed from these diols with acetone under acid catalysis.

A reaction of acetone with both hydroxyl groups of a diol forms a cyclic acetal, which is more commonly known as the acetonide.

Acetals can be easily prepared from corresponding aldehydes and ketones and also it can be converted back to its starting carbonyl compounds. Due to this reason, acetals are very much useful is acting as protecting groups to prevent aldehydes and ketones from reacting with strong bases and nucleophiles.

$\text{1,2}-\text{diols}$ on treatment with acetone under acid catalysis ${\text{(H}}^{\text{+}}{\text{,H}}_{\text{2}}\text{O)}$forms a cyclic ketal (acetonide). The mechanism for the formation of an acetal can be divided into two parts, namely acid-catalyzed addition of a carbonyl which is followed by ${{\text{S}}_{\text{N}}}^{\text{1}}$substitution. Acetals are the most commonly used protecting groups for aldehydes and ketones. The formation of acetonides from the given diols is shown below: