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Alcohols… Alcohols are a homologous series where: • • • • No double bonds present General Formula CnH2n+1OH All exhibit Hydrogen Bonds There are three types; • Primary • Secondary • Tertiary Alcohols… Alcohols undergo the following reaction types: • Combustion • Oxidation using Potassium Dichromate • Esterification • Dehydration Alcohols… Primary alcohols have the functional group at the end of the chain. Attached to the same carbon as the OH is: • 1 alkyl group • 2 Hydrogens e.g. Butan-1-ol Alcohols… Primary alcohols can be oxidised to form carboxyl compounds: Under DISTILLATION conditions CH3CH2CH2CH2OH + [O] CH3CH2CH2CHO Under REFLUX conditions CH3CH2CH2CH2OH + [O] CH3CH2CH2COOH Solution will change from orange to green Alcohols… Secondary alcohols have the OH group in the middle of the chain. Attached to the same carbon as the OH is: • 2 alkyl groups • 1 Hydrogen e.g. Butan-2-ol Alcohols… Secondary alcohols can be oxidised to form ketones: Under REFLUX conditions CH3CH2CH(OH)CH3 + [O] CH3CH2COCH3 Solution will change from orange to green Alcohols… Tertiary alcohols have the OH group next to two branches of the chain. Attached to the same carbon as the OH is: • 3 alkyl groups • 0 Hydrogens e.g. 2-methylpropan-2-ol Alcohols… Tertiary alcohols cannot be oxidised, under any conditions. Under REFLUX conditions CH3C(CH3)(OH)CH3 + [O] Solution will remain orange Alcohols… D Alcohols… We can use oxidation reactions (and the products) to identify unlabelled primary, secondary and tertiary alcohols. Suggest a method to do so. Alcohols… 1. Heat all three unknowns under reflux with Potassium Dichromate. 2. Mixture containing tertiary alcohol will remain orange. 3. Test the green solutions with sodium carbonate: • Carboxylic acid (from primary alcohol) will fizz • Ketone (from secondary alcohol) will not Alcohols… Alcohols have higher boiling points than their base alkanes due to the presence of two types of intermolecular forces: • Instantaneous dipole-induced dipole from the alkyl chain • Hydrogen bonds from the –OH group Alkanes only have id-id which require less energy to overcome. Alcohols… Explain the trend in the boiling point of the alcohols (4 marks) • Increased contact between the hydrocarbon chains • Increased Instantaneous dipole – induced dipole • Increased energy required to overcome IM forces • Increased boiling point Alcohols… Alcohols are less volatile than their corresponding alkanes due to the strength of their Hydrogen bonds. Volatility, and therefore flammability, decreases as the chain gets longer. Alcohols… Alcohols are soluble in water due to their similar intermolecular forces – both exhibit Hydrogen Bonds Haloalkanes… Haloalkanes are a homologous series where: • No double bonds present • General Formula CnH2n+1X • All are Polar Haloalkanes… The reactivity of a haloalkane is determined by its carbon-halogen bond. The weaker the bond the more reactive the compound. Iodoalkanes are MUCH more reactive than fluoroalkanes. Haloalkanes… Explain why C-X bond strength decreases down group 7 (4 marks) • Atomic radius increases • Distance of covalent bond from nucleus increases • Shielding increases • Less energy required to break the bond Haloalkanes… Haloalkanes contain the subclass of CFCs (chlorofluorocarbons) which are used as: • Refrigerants • Fire safety equipment In the atmosphere CFCs are inert and non-toxic In the stratosphere CFCs deplete ozone Haloalkanes… Homework: Research the Montreal Protocol and the effects of ozone depletion.
