An organic compound that reacts with Br2 is an alkene. Alkenes are hydrocarbons that contain at least one carbon-carbon double bond. The IUPAC name for an alkene is based on the longest carbon chain that contains the double bond. The suffix "-ene" is added to the root name of the alkane with the same number of carbon atoms.

For example, the IUPAC name for the alkene with the formula CH2=CH2 is "ethene". The longest carbon chain is two carbons long, and the root name of the alkane with two carbon atoms is "eth-". The suffix "-ene" is added to "eth-" to give the name "ethene".

Other examples of alkenes include:

* Propene: CH2=CHCH3

* Butene: CH2=CHCH2CH3

* Pentene: CH2=CHCH2CH2CH3

Alkenes are unsaturated hydrocarbons, which means that they have fewer hydrogen atoms than the corresponding alkane. This makes alkenes more reactive than alkanes. Alkenes can undergo a variety of reactions, including addition reactions, substitution reactions, and polymerization reactions.