Protecting groups play an important role in organic synthesis. Their role is increasing chemoselectivity . In many syntheses of delicate organic compounds, some specific parts of their molecules cannot survive the required highly reactive reagents and harsh chemical environments (e.g. a boiling acid bath). Then, these parts, or groups, must be protected. For example, lithium aluminum hydride is a highly reactive, but useful reagent, capable of reducing esters to alcohols. It will always react with carbonyl groups, and this cannot be discouraged by any means. When we need both a reduction of an ester and a carbonyl in the end product, the attack of the hydride on the carbonyl has to be prevented. For example, the carbonyl is converted into an acetal, which does not react with hydrides. The acetal is called a protecting group for the carbonyl. After the step involving the hydride is complete, the acetal is removed (by reacting it with an aqueous acid), giving back the original carbonyl. This is called deprotection.
Common protecting groups