Choose functional group from among the following.
Bromine reacts with 2-butene to form 2,3-dibromobutane.
It also reacts with 3-methyl-2-pentene to form 2,3-dibromopentane.
Instead of trying to memorize both equations, we can build a general rule that bromine reacts with compounds that contain a C=C double bond to give the product expected from addition across the double bond. This approach to understanding the chemistry of organic compounds says that certain atoms or groups of atoms known as functional groups give these compounds their characteristic properties.
In this case, we can predict the properties of a molecule where the double bond is present.
This can be extended to all such molecules like -OH, or -COOH which give some characteristic properties to molecules.