Edexcel A Level Chemistry Topic 6: Organic Chemistry I Exam Questions

About Edexcel A Level Chemistry Topic 6: Organic Chemistry I

Topic 6 of Edexcel A Level Chemistry, Organic Chemistry I, introduces the core organic families. You learn nomenclature, formula types and structural and E/Z isomerism, then study alkanes as fuels, including cracking, reforming, pollutants and alternative fuels, and the free radical substitution mechanism. Alkenes are covered through electrophilic addition mechanisms, the test with bromine water, oxidation with potassium manganate(VII) and addition polymers. Halogenoalkanes cover nucleophilic substitution and elimination, and alcohols cover combustion, oxidation, halogenation and dehydration, with practical techniques such as reflux and distillation. It is assessed in Paper 2 (Advanced Organic and Physical Chemistry). Examiners frequently test mechanisms, E/Z naming and reagents and conditions.

What you need to know

• Nomenclature and isomerism Name compounds using IUPAC rules and draw displayed, structural and skeletal formulae. E/Z isomerism arises from restricted rotation about C=C with two different groups on each carbon, using Cahn-Ingold-Prelog priorities.
• Alkanes and fuels Crude oil is separated by fractional distillation, then cracked to make smaller alkanes and alkenes and reformed to make branched and cyclic hydrocarbons for petrol. Combustion produces CO, NOx, SO2 and particulates, and biofuels are an alternative.
• Free radical substitution Initiation: Cl2 → 2Cl• in UV light; propagation steps produce the halogenoalkane and regenerate Cl•; termination removes radicals. Further substitution gives a mixture of products.
• Alkenes Electrophilic addition with H2, halogens, hydrogen halides and steam. With HBr, the major product forms via the more stable carbocation. Bromine water decolourises, and acidified KMnO4 forms a diol.
• Halogenoalkanes Hydrolysis rate (with aqueous AgNO3 in ethanol) increases from C-Cl to C-I as bond enthalpy falls. Nucleophilic substitution with OH-, NH3 and CN-; elimination with KOH in ethanol.
• Alcohols Primary alcohols are oxidised by acidified K2Cr2O7 to aldehydes (distil) or carboxylic acids (reflux), secondary to ketones; tertiary are not oxidised. Alcohols form halogenoalkanes with PCl5 or HBr and dehydrate with phosphoric acid.
• Practical techniques Know heating under reflux, distillation, separating funnel use, drying with anhydrous salts and redistillation for purification.

Common mistakes in Topic 6: Organic Chemistry I

• Labelling E/Z isomers by whether identical groups are on the same side instead of using priority rules.
• Starting curly arrows from atoms rather than from bonds or lone pairs.
• Using aqueous KOH for elimination; the Edexcel condition is KOH in ethanol, heated.
• Saying a carbocation forms in the free radical mechanism; radicals have unpaired electrons, not charges.
• Distilling when the question asks for a carboxylic acid; reflux is needed for full oxidation.

Try three Topic 6: Organic Chemistry I exam-style questions