alcohol facts

• What are alcohols?

  • Alcohols are compounds that contain at least one hydroxy (-OH) group
  • The general formula of alcohols is CnH2n+1OH
  • Alcohols can be prepared by a wide range of chemical reactions
• What unique bond is in alcohols?

  • In an alcohol, there are O-H bonds present in the structure
  • Therefore hydrogen bonds set up between the slightly positive hydrogen atoms (δ+ H) and lone pairs on oxygens in other molecules
  • The hydrogen atoms are slightly positive because the bonding electrons are pulled away from them towards the very electronegative oxygen atoms
• Do alcohols, or alkanes have higher boiling points?

  • In alkanes, the only intermolecular forces are temporary induced dipole-dipole forces
  • Hydrogen bonds are much stronger than these and therefore it takes more energy to separate alcohol molecules than it does to separate alkane molecules
  • Therefore, the boiling point of alkanes is lower than the boiling point of the respective alcohols
  • For example, the boiling point of propane is -42 oC and the boiling point of propanol is 97 oC
• As well as hydrogen bonds, what other bond is present in alcohols?

  • As with all molecules, there are also temporary induced dipole-dipole forces (LDF) between alcohols
  • The boiling points increase as the number of carbon atoms in the chains increases. It takes more energy to overcome the temporary induced dipole-dipole forces and so the boiling points rise
  • This is because the dipole is caused by the changing position of the electron cloud, so the more electrons there are, the larger the temporary induced dipole-dipole forces will be
• Are alcohols soluble in water?

  • The small alcohols are completely soluble in water
  • If they are mixed with water, there will be one solution
  • However, solubility falls as the length of the hydrocarbon chain in the alcohol increases
  • The hydrocarbon chains are forcing their way between water molecules and so breaking hydrogen bonds between those water molecules
  • The -OH end of the alcohol molecules can form new hydrogen bonds with water molecules, but the hydrocarbon can not form hydrogen bond
• What are primary alcohols?

  • Primary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to one other carbon atom (or alkyl group). 
• What are secondary alcohols?

  • Secondary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to two other carbon atoms (or alkyl groups)
• What are tertiary alcohols?

  • Tertiary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to three other carbon atoms (or alkyl groups)
• What is the general formula of an alcohol?

  CnH2n+1OH
• What kind of intermolecular bonding do alcohols have?

  hydrogen bonding, due to the electronegativity difference in the OH bond
• Are alcohols soluble in water?

  soluble when short chain- OH hydrogen bonds to hydrogen bond in water

  insoluble when long chain- non polarity of C-H bond takes precedence
• What happens when you mix an alcohol with water?

  hydrogen bonds form between the -OH and H2O ...