What is the order of reactivity of halogen and alkyl groups in the dehydrohalogenation ofalkyl halides to give alkenes?

The order of reactivity of halogens in the dehydrohalogenation of alkyl halides to give alkenes is as follows: Iodine (I) > Bromine (Br) > Chlorine (Cl) > Fluorine (F). This order is due to the bond strength of the carbon-halogen bond, with iodine having the weakest bond and therefore being the most reactive.

The order of reactivity of alkyl groups is tertiary (3°) > secondary (2°) > primary (1°). This is due to the stability of the carbocation intermediate formed during the reaction. Tertiary carbocations are more stable than secondary carbocations, which are more stable than primary carbocations. Therefore, tertiary alkyl halides are the most reactive in dehydrohalogenation reactions.