What are common addition reactions involving alkenes?

Common addition reactions involving alkenes include hydrogenation, halogenation, hydrohalogenation, and hydration.

Hydrogenation is a reaction where hydrogen is added across the double bond of an alkene to form an alkane. This reaction is typically carried out in the presence of a catalyst such as nickel, platinum or palladium. The process is used extensively in the food industry to convert unsaturated fats and oils into saturated fats, which are solid at room temperature.

Halogenation is another common addition reaction involving alkenes. In this reaction, a halogen such as chlorine or bromine is added across the double bond. The result is a dihalogeno compound. This reaction is often used in the laboratory to test for the presence of a carbon-carbon double bond, as the colour of the halogen disappears when it reacts.

Hydrohalogenation involves the addition of hydrogen halides (HX where X is a halogen) to alkenes. The hydrogen and halogen add across the double bond to form a haloalkane. This reaction follows Markovnikov's rule, which states that in the addition of a protic acid HX to an alkene, the acid hydrogen (H) becomes attached to the carbon with fewer alkyl substituents, and the halide (X) group becomes attached to the carbon with more alkyl substituents.

Lastly, hydration is the addition of water (H2O) across the double bond of an alkene to form an alcohol. This reaction also follows Markovnikov's rule. It is typically carried out in the presence of a strong acid, such as sulphuric acid, which acts as a catalyst.

These addition reactions are fundamental to organic chemistry and have wide-ranging applications in industry and laboratory settings. They provide a way to transform alkenes into a variety of other useful organic compounds.