Alkanes Essay

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Alkanes - CnH2n+2 Trends in melting point, boiling point and volatility can be explained by the weak intermolecular forces called induced dipole - induced dipole forces (van der Waal's forces). As the chain length of alkanes increases, so does the number of electrons, which increases the strength of the van der Waal forces. Branching reduces the surface area over which induced dipole - induced dipole forces can act. Alkanes are non-polar molecules, so do not react with polar reagents. Free radicals are produced by the homolytic fission of covalent bonds, for which light can provide energy. Alkanes will react with free radicals - free radical subtitution. Alkenes Alkenes are more reactive than alkanes because of the presence of the electron rich double bond. Alkenes react by electrophilic addition: With halogens to give dihalogenoalkanes. Hydrogen to give alkanes. Hydrogen halides to give halogenoalkanes. Water to give alcohols. Alkenes can be oxidised by cold dilute potassium manganate (VII) to give diols. Alkenes can be oxidised by hot acidified concentrated potassium manganate (VII) to give carbonyl compounds, the reaction cleaving the carbon-carbon bond. Halogenoalkanes Halogenoalkanes can be prepared by the reaction of alcohols with concentrated hydrobromic acid, concentrated hydrochloric acid and concentrated hydroiodic acid or by the reaction of the appropriate phosphorus halides with an alcohol. Halogenoalkanes react by nucleophilic substitution With cyanide ion to form nitriles. Ammonia to give amines. Aqueous hydroxide ion to give alcohols. Halogenoalkanes can eliminate hydrogen halides to form alkenes when treated with hot ethanolic alkali. Alcohols Alcohols contain the hydroxyl, OH, functional group attached directly to a carbon atom. Short chain alcohols are soluble in water but long chain are not. Primary alcohols can be

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