📝 Halogenoalkanes

Task

🎧️ Listen to the recording and mind pronunciation of words.

If one or more of the hydrogen atoms in an alkane molecule are replaced by halogen atoms, the compound is called a halogenoalkane. Iodoalkanes are the most reactive halogenoalkanes, whereas fluoroalkanes are the least reactive. This is explained by the trend in the bond strength of the carbon–halogen bonds. The C-F bond is the strongest bond, and the C-I, bond is the weakest bond. So, the C-I bond is most easily broken during its reactions. Halogenoalkanes are attacked by nucleophiles. A nucleophile is a species with a lone pair of electrons which it can use to bond with an electropositive carbon atom on an organic molecule. Suitable nucleophiles include aqueous alkali, OH– (aq), cyanide, CN–, and ammonia, NH₃.
The reaction with OH–ions (or with water) is known as hydrolysis, and an alcohol is formed. Halogenoalkanes will also undergo elimination reactions when heated with ethanolic sodium hydroxide, forming alkenes.
The fluoroalkanes and fluorohalogenoalkanes have many uses, including anaesthetics solvents, refrigerants and aerosol propellants. Chlorofluoroalkanes have been responsible for damaging the Earth’s ozone layer, but alternative inert compounds, such as fluoroalkanes, are now replacing the use of CFCs.

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