Alcohols 🍻

• What are alcohols?

  Alcohols are organic compounds that contain a hydroxyl (-OH) functional group attached to a carbon atom. They have a general formula of CnH2n+1OH
• comparison in physical melting points between alcohols and alkanes?

  • Alkanes= hydrogen and carbon= similar electronegativity= non polar molecules therefore weak london forces (Intermolecular forces)
  • alcohols= electronegativity between O and H= different therefore polar= stronger hydrogen bonds= higher melting points
• how does hydrogen bonds look between two ethanol molecules?


  .

  
• comparison in volatility and boiling point of alkanes and alcohols?

  in liquid state= alcohols held together by hydrogen bonds- more energy required to break these than the weak London forces in alkanes therefore more volatile
• comparison of solubility in water of alkanes and alcohols?

  hydrogen bonds= allow compounds to be more soluble than a compound without H bonds

  • alkanes= non polar= cant form H bonds with water

  the longer the hydrocarbon chain= less influence by the-OH group therefore solubility decreases
• what is a primary, secondary and tertiary alcohol?

  Primary: the -OH is attached to the carbon atom that’s attached to 2 hydrogen and 1 alkyl group Secondary: the -OH is attached to the carbon atom that is attached to 1 hydrogen atom and 2 alkyl groups Tertiary: the -OH is attached to the carbon atom attached to No hydrogen atoms and 3 alkyl groups
• combustion of alcohol?


  burn in plentiful oxygen and combust completely- producing carbon dioxide and water
• what happens during oxidation of an alcohol and what conditions are required?

  • potassium dichromate K2Cr2O7 acidified with dilute sulfuric acid H2SO4
  • causes orange solution to reduce to a green solution containing chromium ions

  
• what are the products of oxidising a primary alcohol? What is the prep to form a aldehyde?


  • oxidised into aldehyde or carboxylic acid
  • aldehyde can be oxidised into carboxylic acid
  • To ensure an aldehyde is produced the aldehyde has to be distilled as soon as it forms to prevent further reaction with the oxidising agent

  
• what is the preparation of oxidation to form a carboxylic acid?


  • primary alcohol heated strongly under reflux with excess of potassium dichromate= carboxylic acid
  • excess ensures all the alcohol is oxidised
  • heating under reflux ensures that all the aldehyde initially formed oxidises into carboxylic acid

  
• What are the products of oxidising a secondary alcohol?

  • oxidise using potassium dichromate ions and dilute sulfuric acid under reflux to produce a ketone and water
  • orange to green to show complete oxidation

  
• what happens when tertiary alcohols are oxidised?

  Don't undergo oxidation reactions and the dichromate ions remain orange
• what is the dehydration of alcohol?

  when a water molecule is removed= elimination reaction

  alcohol= heated under reflux

  • in the presence of= acid catalyst and concentrated sulfuric acid or phosphoric acid

  produces and alkene and water

  
• how are haloalkanes formed from alcohols?

  Alcohol reacts with hydrogen halide under reflux with:

  - sulfuric acid and sodium halide