Final answer:
Addition reactions to the double bond of alkenylbenzenes typically involve the breaking of a pi bond and the formation of two new sigma bonds, where electrophiles are added across the double bond. Factors like catalysts and reaction conditions can affect these reactions which often result in a change in carbon atom hybridization from sp² to sp³.
Step-by-step explanation:
How do additions to the double bond of alkenylbenzenes proceed? Alkenylbenzenes are a type of hydrocarbon that include a benzene ring attached to an alkene chain. In the presence of a catalyst such as nickel (Ni) or platinum (Pt), alkenes typically undergo addition reactions where the pi bond in the double bond is broken and two new sigma bonds are formed as atoms or groups are added to the carbons of the double bond.
For instance, the addition of hydrogen (hydrogenation) converts the alkene into an alkane. In the case of alkenylbenzenes, the reaction typically occurs at the alkene part of the molecule. Due to the delocalized electrons in the benzene ring, benzene itself resists addition unless severe conditions are used, like high temperature and pressure alongside a catalyst, which can eventually lead to the hydrogenation of benzene to cyclohexane. However, the reactions on the alkene part of an alkenylbenzene are more akin to alkenes, often involving electrophiles that are attracted to the electron-rich pi bond.
The addition mechanism usually starts with an electrophilic attack, as in the case of free radical initiators or halogens, where one of the pi electrons forms a bond with the incoming electrophile, creating a carbocation intermediate which then quickly reacts with a nucleophile to complete the addition process. The hybridization of the carbon atoms involved in the double bond changes from sp² to sp³ as a result of the addition reaction.