Alkenes

Elimination of HX from a halogenoalkane requires ethanolic NaOH and heat. The reaction produces an alkene, NaX, and water.

Alcohols can be dehydrated using either a heated catalyst (

The hydrogenation of an alkene requires hydrogen gas (H₂(g)) and a platinum or nickel catalyst (Pt/Ni) with heat. This reaction converts the alkene into an alkane.

The addition of steam to an alkene requires water as steam (H₂O(g)) and a phosphoric acid catalyst (H₃PO₄). This reaction converts the alkene into an alcohol.

Bromine becomes polarised as it approaches the alkene. The π electrons of the C=C bond attack the partially positive bromine, forming a cyclic bromonium ion intermediate. A bromide ion then attacks the carbon, breaking the bromonium ion and forming a dibromoalkane.

Markovnikov's rule states that in the addition of HX to an alkene, the hydrogen atom adds to the carbon with more hydrogen atoms already attached. This is because the more substituted carbocation intermediate (tertiary > secondary > primary) is more stable due to the inductive effect of alkyl groups donating electron density.

Oxidation by hot concentrated acidified KMnO₄ leads to the rupture of the carbon-carbon double bond. Depending on the alkene, the products can include ketones, carboxylic acids, or carbon dioxide, which depend on the substituents on the C=C.