Organic Synthesis

Full Notes

Organic Practical Techniques

Quickfit Apparatus

Used to assemble secure and leak-proof setups for key organic processes:

Example Distillation

Separates compounds by boiling point

Allows collection of a product as it evaporates and recondenses

Example Reflux

Heats a reaction mixture over time without losing volatile components

Vapours rise, condense, and drip back into the mixture to ensure complete reaction

Purification of Organic Liquids

After synthesis, the organic product usually contains impurities (unreacted chemicals, water, solvents):

Example Separating funnel

Separates immiscible layers (e.g. organic solvent and water)

The denser layer settles at the bottom and is drained off

Matt’s exam tip

The aqueous layer is usually denser, so it tends to sit at the bottom. But this isn’t always the case — always check the density data in the question. The denser liquid forms the lower layer, the less dense sits on top.

Example Drying the organic layer

Add anhydrous drying agents (e.g. MgSO₄ or CaCl₂) to remove water

Solid clumps form as water is absorbed → once dry, solution is clear

Example Redistillation

Further purification by boiling and collecting only the fraction at the correct boiling point

Useful when separating organic liquids with close boiling points

Identifying Functional Groups and Predicting Reactions

Organic molecules often contain multiple functional groups.

Being able to recognise these allows you to:

• Predict chemical behaviour
• Suggest appropriate reagents and reaction conditions
• Plan synthesis or identify unknown compounds

Examples:

• Alcohols (–OH): undergo oxidation, elimination, substitution
• Alkenes (C=C): undergo electrophilic addition
• Haloalkanes (C–X): undergo nucleophilic substitution
• Carbonyls (C=O): undergo nucleophilic addition, form derivatives
• Carboxylic acids (–COOH): form salts, esters, amides

Understanding the reactivity of each group and how they interact with each other is key to predicting reactions.

Two-Stage Synthetic Routes

You are expected to be able to plan a sequence of reactions to convert one compound into another using two synthetic steps.

This involves identifying starting and target functional group and then choosing appropriate reagents and conditions

Matt’s exam tip

Synthesis questions can look overwhelming! Focus on one thing at a time and remember that no matter how complicated the molecules may look, the functional group conversions will only be ones you have seen and learnt about before. Focus on the functional groups in the molecules that are changing, rather than focusing on the whole molecule overall.

Example Route: Alkene → Alcohol → Carboxylic Acid

Convert an alkene (e.g. ethene) to an alcohol (e.g. ethanol), then to a carboxylic acid (e.g. ethanoic acid):

• Step 1: Alkene → Alcohol
  • Reagents: H₂O(g), conc. H₃PO₄
  • Reaction: Addition
• Step 2: Alcohol → Carboxylic Acid
  • Reagents: K₂Cr₂O₇ + H₂SO₄
  • Reaction: Oxidation (reflux conditions)

The exam may also give extra reagents or information not explicitly taught, to extend your toolkit and test your understanding.

Summary

• Quickfit apparatus enables safe distillation and reflux.
• Purification uses separating funnels, drying agents and redistillation.
• Recognising functional groups helps predict reactions and tests.
• Two-step routes combine known reactions and conditions to reach a target.