Addition Reactions of Alkenes

Unsaturated Compounds

• Unsaturated compounds can combine directly with other substances to form a new compound.
• Alkanes are saturated hydrocarbons and react by substitution.

Addition Reactions of Alkenes

• Addition of hydrogen (hydrogenation): the reaction is an important stage in the conversion of vegetable oils into margarine.
• Addition of halogens (halogenation):
  • The order of reactivity of halogens with alkenes is F > Cl > Br > I.
  • The reaction with fluorine is rather explosive, while chlorine and bromine react rapidly at room temperature.
  • The halogen is added across the double bond.
• Addition of hydrogen halides (hydrohalogenation):
  • The reactivity order of hydrogen halides with alkenes is HI > HBr > HCl > HF.
  • Ethene combines with hydrogen iodide and hydrogen bromide at room temperature with anhydrous aluminium III chloride as a catalyst.
• Addition of water (hydration):
  • Hydration is achieved indirectly with tetraoxosulphate (VI) acid, resulting in the formation of alcohols.
• Addition of oxygen (oxidation):
  • Baeyer's reagent (a cold KMnO4 alkaline solution) oxidizes ethane to ethane-1,2 diol (ethylene glycol).

Uses of Ethyne

• Ethyne is used in oxyacetylene flame for welding and cutting steel.
• It is used to prepare non-flammable industrial solvents, such as trichloroethene and tetrachloroethene.
• Ethyne is a good starting material for the synthesis of other important organic compounds, such as ethanoic acid.

Functional Groups

• Various functional groups are listed, including:
  • Alcohols (R-OH)
  • Amines (R-NH2)
  • Thiols (R-SH)
  • Chlorides (R-Cl)
  • Aldehydes (R-CHO)
  • Ketones (R-COR)
  • Bromides (R-Br)
  • Iodides (R-I)
  • Amides (R-CO-NH2)
  • Acid chlorides (R-CO-Cl)
  • Carboxylic acids (R-COOH)
  • Anhydrides (R-CO-OCOR)
  • Esters (R-CO-OR)
  • Imine (R-CH=NR)
  • Nitro group (R-NO2)
  • Ether (R-OR)

Aldehydes and Ketones

• General formula: Aldehydes and ketones contain the carbonyl group.
• Definition:
  • Aldehydes have the carbonyl group attached to a carbon atom at the end of a carbon chain.
  • Ketones have the carbonyl group attached to a carbon atom within the carbon chain.
• Examples of aldehydes and ketones are given.
• Nomenclature rules for aldehydes and ketones are outlined.

Five General Reactions of Aldehydes and Ketones

• Nucleophilic addition
• Reduction reaction
• Oxidation reaction
• Halogenation
• Reaction with alkalis

Aldol Condensation

• Aldol condensation is an organic reaction in which an enolate ion reacts with a carbonyl compound to form β-hydroxyketone or β-hydroxyaldehyde, followed by dehydration to give a conjugated enone.
• Aldol condensation plays a vital role in organic synthesis, creating a path to form carbon-carbon bonds.

Nitriles (R-CN)

• The prefix "cyano-" is used interchangeably with the term "nitrile" in industrial literature.
• Nitriles are found in many useful compounds, including methylcyanoacrylate used in superglue and nitrile rubber.
• Nitrile rubber is widely used as automotive and other seals due to its resistance to fuels and oils.
• Organic compounds containing multiple nitrile groups are known as cyanocarbons.

Learn about the addition reactions of alkenes, including hydrogenation and halogenation, and their reactivity with different substances.