The given compounds can be classified as primary, secondary and tertiary halides by knowing which carbon the halogen atom is attached to. In 1-Bromobut-2-ene, the –Br is attached to the first carbon in the chain, which is a primary carbon atom. The structure is H₃C—HC=CH—H₂C—Br and this is a primary halide

In 4-Bromopent-2-ene, the bromine is attached to the secondary carbon atom, hence this a secondary halide. The structure is CH₃—CH(Br)CH=CH—CH_3.

In 2-Bromo-2-methylpropane, the bromine is attached to the tertiary carbon atom, making it a tertiary halide. The structure is CH₃—C(Br)(CH₃)—CH₃.