Alcohols

• What is the general formula for alcohol?

  CnH2n+2O // CnH2n+1OH
• What is the functional group of alcohols?

  Hydroxyl group ( -OH )
• Why does boiling point increases as the carbon chain length increases?

  • More Carbon atoms
  • More electrons
  • Stronger London forces
  • More energy required to break these forces to separate the molecules
• Why are alcohols soluble?

  They can form hydrogen bonds with water (the hydroxyl groups form hydrogen bonding with water).
• Why are alcohols polar molecules?

  Presence of a hydroxyl group - the polarity arises from the difference in electronegativity between oxygen and hydrogen atoms.
• What is the strongest type of intermolecular force on alcohols?

  Hydrogen bonding
• Why does the solubility decrease as the carbon chain length increases?

  • As the carbon chain is non-polar, when the chain length increases, the hydrogen bonding between the alcohol and water molecule is disrupted -> decreases solubility.
  • Alkanes are non-polar and cannot form hydrogen bonds with water.
• Why do alcohols have a higher boiling than their alkane counterparts?

  • As alcohol molecules are polar molecules, they form hydrogen bonds (because the -OH group is polar) between themselves.
  • As they also have London Forces between molecules, more energy is required to separate molecules -> higher boiling point -> less volatile
• • Alcohols can be classified as either primary, secondary or tertiary.
  • It depends on the number of alkyl groups attached to the carbon atom joined to the -OH group.
  • 0/1 alkyl group - primary alcohol
  • 2 alkyl groups - secondary alcohol
  • 3 alkyl groups - tertiary alcohol
• • Alcohols can be oxidised (not combustion) by heating the alcohol with a mixture of potassium dichromate (K2Cr2O7) and dilute sulphuric acid (H2SO4).
  • Colour change is from orange to green.
  • Primary alcohols are oxidised to aldehydes and carboxylic acids.
  • Secondary alcohols are oxidised to ketones.
  • Tertiary alcohols do not undergo oxidation with K2Cr2O7
• The complete combustion of alcohols

  • Alcohols burn completely in an excess supply of oxygen, breaking all the C-C and C-H bonds. This produces carbon dioxide, water, and the release of a large quantity of energy in the form of heat.
• • If the primary alcohol is heated gently using distillation with a limited amount of potassium dichromate, an aldehyde is formed as it's distilled put, preventing further oxidation.
  • If the primary alcohol is heated under reflux conditions with an excess amount of potassium dichromate, a carboxylic acid is produced as reflux prevents the aldehyde from escaping, so it is oxidised again, into a carboxylic acid.
• Name and describe the position of the functional group in aldehyde

  • The functional group of aldehyde is the carbonyl (C=O) group
  • Located at the end of the carbon chain.
• Name and describe the position of the functional group in ketones

  • The functional group of ketones is the carbonyl (C=O) group
  • Located within the body of the carbon chain.
• Alcohol Substitution Reaction - Synthesis of Haloalkane

  • Alcohols react gently with hydrogen halide to produce a haloalkane.
  • The alcohol is heated under reflux with dilute sulphuric acid and sodium halide.
  • The hydrogen halide formed then reacts with the alcohol.
• Alcohol Substitution Reaction - Synthesis of Haloalkane [e.g.]

  • NaBr + H2SO4 ----> NaHSO4 + HBr
  • C2H5OH + HBr ----> C2H5Br + H20
• Dehydration of Alcohols

  • A reaction where water is removed from the alcohol
  • The alcohol is heated under reflux with a n acid catalyst such as concentrated sulphuric acid, concentrated phosphoric acid, or heated aluminium oxide powder.
  • This reaction is an example of an elimination reaction, where a small molecule is removed from a molecule, forming tow products.
  • Alcohol ----> Alkene + Water
• Dehydration of Alcohols [e.g.]

  CH3CH2CH2OH ----> CH3CH=CH2 + H2O