Alkenes in the gas or liquid phase can react with hydrogen in the presence of an appropriate catalyst. The number of double bonds can be determined by the microhydrogenation method.

Alkenes undergo addition reactions with halogens, usually chlorine or bromine.

Markov's rule: When asymmetric alkenes and hydrogen halides are added, hydrogen atoms are mainly added to the double-bonded carbon atoms containing more hydrogen.

Anti-Markovitch rule: The addition of propylene and hydrogen bromide, if peroxide is present, will result in the opposite result to the Markovitch rule. The main product is 1-bromopropane (hydrogen chloride and hydrogen iodide still comply with the Markovitch rule)

Under the oxidation of osmium tetroxide, alkenes are almost quantitatively oxidized to vicinal diols

In the presence of dilute and cold potassium permanganate, alkenes are oxidized to vicinal diols.

In the presence of heating and concentrated potassium permanganate, the carbon chain breaks at the double bond, producing carboxylic acids and ketones with fewer carbon atoms. The above reaction can be used to test the presence of double bonds and to infer the structure of the reactant molecules from the product structure.

Ozone can quickly react quantitatively with alkenes to form cyclic ozonides, which is called an ozonation reaction. Because it contains peroxy bonds (—O—O—), it is very unstable and prone to explosion. Therefore, the next reaction is usually carried out in the solution or decomposed into aldehydes or ketones by adding water. Zinc can be added to prevent the aldehyde from being oxidized into acid by hydrogen peroxide. The above reaction can also identify the position of double bonds in alkenes.

Alkynes are partially hydrogenated to form alkenes and completely hydrogenated to form alkanes.

Alkynes can also add to chlorine or bromine. The reaction proceeds in two steps, the first to generate dihalogen derivatives of alkenes, and the second to generate tetrahalogenated alkanes.

The addition of alkynes and hydrogen halide occurs in two steps. The addition reaction of unsymmetrical alkynes and hydrogen halides does not follow Markov's rule. In the presence of peroxide, the addition reaction of asymmetric alkynes and HBr follows the anti-Markovitch rule.

The hydration of alkynes is carried out according to Markov's rule in the presence of a catalyst (mercuric sulfate in sulfuric acid solution).

Acetylene is oxidized by potassium permanganate to form carbon dioxide, and other alkynes are oxidized by potassium permanganate to form carboxylic acids. You can see that the purple color of potassium permanganate fades, you can also check the carbon-carbon triple bond and infer the structure of the reactant molecules from the structure of the product.

Alkynes react with ozone to form two carboxylic acids

At lower temperatures and in non-polar solvents, 1,2-addition is favored; at higher temperatures and in polar solvents, 1,4-addition is favored

Conjugated dienes and compounds containing carbon-carbon double bonds and triple bonds (those with carbonyl or carboxyl groups on their flanks) can undergo a 1,4-addition reaction to generate a six-membered cycloalkene compound, which is called a diene synthesis reaction ( Pericyclic reaction, synergistic reaction), only need to be heated to react. The Diels-Alder reaction plays a very important role in organic synthesis and can also determine conjugated double bonds in organic compounds.