A protecting group or protective group is introduced into a molecule by chemical modification of a functional group

Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

 in order to obtain chemoselectivity

Chemoselectivity

Chemical reactions are defined usually in small contexts , such generalizations are a matter of utility. The preferential outcome of one instance of a generalized reaction over a set of other plausible reactions, is defined as chemoselectivity...

 in a subsequent chemical reaction. It plays an important role in multistep organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

.

In many preparations of delicate organic compounds, some specific parts of their molecules cannot survive the required reagents or chemical environments. Then, these parts, or groups, must be protected.