Organic Reactions — Flashcards & Quiz

Key Points

• Substitution (alkanes): X₂ + UV light replaces an H with a halogen; product is an alkyl halide plus HX.
• Addition (alkenes): the C=C double bond breaks and two new bonds form. Examples include bromination, hydrogenation, hydration, and HX addition.
• Oxidation of alcohols: primary → aldehyde → carboxylic acid (using KMnO₄ or K₂Cr₂O₇); secondary → ketone (stops there); tertiary resists oxidation.
• Esterification: carboxylic acid + alcohol ⇌ ester + water, catalysed by concentrated H₂SO₄. It is reversible (acidic hydrolysis returns the reactants).
• Saponification: base hydrolysis of an ester gives the sodium carboxylate salt plus the alcohol — the basis of soap making.
• Markovnikov's rule: when HX adds to an unsymmetrical alkene, H bonds to the carbon with more hydrogens (the other gets X).

Common Mistakes to Avoid

1. Confusing substitution (alkanes) with addition (alkenes) — they are characteristic of different functional groups.
2. Forgetting to balance the equation and include the catalyst (UV, H₂SO₄, heat).
3. Claiming tertiary alcohols can be oxidised — they resist oxidation because there is no H on the carbon bearing the –OH.
4. Missing Markovnikov's rule when adding HX to an unsymmetrical alkene.
5. Mixing up esterification (Fischer, acid-catalysed) with saponification (base hydrolysis).

Exam Strategy

QCAA Unit 4 organic reaction questions ask you to predict products or write equations for named reactions. Method: (1) identify the starting material and functional group, (2) match to the appropriate reaction type, (3) write the product with correct IUPAC name, (4) balance the equation and include conditions (catalyst, temperature, light). Draw structures where helpful — they make mechanism clearer than words.

Revision Tip

Organic reaction pathways are pattern recognition — drill a Revizi flashcard deck pairing each functional group with its characteristic reaction and product.