There are many organic organic compounds which tends to reacts with Br₂. Specifically speaking two classes of organic compounds are very well known for their reaction with Br₂. Those two classes are alkenes and alkynes. Both belongs to unsaturated hydrocarbons.
This reaction of Unsaturated Hydrocarbons with Br₂ are generally used for the identification of Unsaturation.
Examples:
H₂C=CH₂ + Br₂ → Br-CH₂-CH₂-Br
In above reaction Ethene on reaction with Br₂ produces 1,2-Dibromoethane. In this reaction the color of Br₂ (yellow-brown) disappears as the reaction proceeds.
HC≡CH + 2 Br₂ → Br₂HC-CHBr₂
In this reaction acetylene (alkyne) reacts with two moles of Br₂ to produce 1,1,2,2-Tetrabromoethane.
Hence, every alkene and alkyne for example, Ethene, 1-Butene, 2-Butene 1-Pentene, 2-Pentene, Acetylene, 1-Butyne, 2-Butyne, 1-Pentyne, 2-Pentyne, e.t.c can react with Br₂.