Which mechanism(s) give(s) alkenes as the major products, Sn1, Sn2, E1, or E2?
E1 and E2 mechanisms give alkenes at the products.
In organic chemistry, an elimination reaction is a reaction in which two substituents are removed from a molecule to form an alkene.
The substituents are usually from adjacent carbons.
Most often, one of them is a hydrogen atom and the other is called the leaving group.
An E2 elimination is a concerted one-step process in which the leaving group X departs at the same time as the base B attacks the β hydrogen.
An E1 elimination is a two-step process.
In the first (and rate-determining) step, the leaving group X departs to form a carbocation.
In the second step, the base B attacks the β hydrogen atom and forms the alkene,