Alcohols

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  • Alcohols
    • Hydroxyl group - OH
    • Alkoxy group - OR
    • General formula R-OH
    • Derived from alkanes, substituting the H with an OH
    • Think of alcohols being derived from water by replacing one of the H atoms with an alkyl group
      • In both water and alcohol molecules, hydrogen bonds form between them
        • Hydrogen bonding between alcohol and water molecules explains why they mix
    • Like water, alcohol molecules are polar --> polarised OH bond
    • In both water and alcohol molecules, hydrogen bonds form between them
      • Hydrogen bonding between alcohol and water molecules explains why they mix
    • Alcohols with a small Mr are more soluble than those of a bigger Mr
    • Primary - at the end of a chain
      • If the aldehyde is required, it will be distilled from the reaction mixture. Otherwise, it'll be heated under reflux.
    • Secondary - in the middle of a chain
      • Tertiary - attached to a C atom that carries no H atoms
        • Difficult to oxidise as they don't have a H atom on the C atom to which the -OH is attached
      • Oxidised to form ketones, heated under reflux
        • Cannot oxidise further is it would involve breaking a C-C bond
    • Tertiary - attached to a C atom that carries no H atoms
      • Difficult to oxidise as they don't have a H atom on the C atom to which the -OH is attached
    • Oxidised by heating under reflux with an acidified solution of potassium dichromate(VI)
      • The orange dichromate(VI) ion, Cr2O2(2-)(aq) is reduced to green Cr(3+)(aq)
      • Oxidation of the -OH group will not occur unless there's a H on the C atom to which the -OH is attached
        • The product is a carbonyl compound - an aldehyde or ketone
          • Primary alcohols oxidise to aldehydes, which then are oxidised to a carboxylic acid
            • If the aldehyde is required, it will be distilled from the reaction mixture. Otherwise, it'll be heated under reflux.

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