ALKENE REACTIONS

Hydrogenation of Alkenes
Alkenes are hydrogenated in the presence of a catalyst (Pt, Pd), converting into alkanes. It is a stereospecific SIN reaction, with both hydrogens entering from the same face of the alkene. Hydrogenation occurs from the less hindered side of the molecule, producing a major stereoisomer.

Hydration and Halogenation of Alkenes
The double bond in alkenes attacks electrophiles like protons, polarized halogens, and mercury salts, forming a carbocation that is attacked by nucleophiles in the medium. Alternatively, a cyclic ion may form, opening by nucleophile attack at the more substituted carbon.

Hydroboration
Alkenes react with borane followed by oxidation with hydrogen peroxide to form anti-Markovnikov alcohols. It is a stereospecific SIN reaction, with boron and hydrogen entering from the same face of the alkene.

Oxidation with MCPBA
Peroxycarboxylic acids transfer an oxygen atom to the alkene, forming oxacyclopropanes. In molecules with multiple double bonds, using one equivalent of MCPBA allows specific reaction on the more substituted alkene.

Formation of SIN Diols
Permanganate and osmium tetroxide react with alkenes to form SIN diols. Although OsO₄ has very good yield, it is highly toxic.

Oxidative Cleavage with Ozone
Ozonolysis breaks double bonds, generating aldehydes and ketones. It uses ozone as a reagent, followed by reduction with Zn in acetic acid.

Radical Reactions of Alkenes
HBr/ROOR radical reactions place a bromine on the less substituted carbon of the alkene (anti-Markovnikov).

Polymerization of Alkenes
This is the most important reaction from an industrial perspective. For example, polymerization of ethylene (ethene) produces polyethylene, used in making plastic bags. Polymerization of propylene produces polypropylene. Teflon is obtained by polymerizing tetrafluoroethylene.