This topic develops the ability to apply known organic reactions systematically, selecting and combining transformations to plan efficient synthetic routes between functional groups.

Purpose of a Reaction Toolkit

In organic synthesis, students are expected to apply a reaction toolkit rather than memorise isolated reactions. This means recognising which familiar transformations can be used to convert one functional group into another and combining them logically. The emphasis is on application, not recall, and on using reactions already encountered in Module 4.

A reaction toolkit consists of:

• Known functional group interconversions

• Typical reagents and conditions

• Awareness of reaction limitations and compatibility

• Logical sequencing of reactions to reach a target molecule

Functional Groups within the Toolkit

Only functional groups encountered in Module 4 are relevant. These include:

• Alkanes

• Alkenes

• Haloalkanes

• Alcohols

• Aldehydes

• Ketones

• Carboxylic acids

Students must recognise how these groups relate to one another through common reactions such as oxidation, reduction, substitution, elimination, and hydrolysis.

Core Transformations to Apply

When applying the toolkit, transformations should be selected from familiar chemistry rather than invented.

Oxidation Reactions

Oxidation reactions are commonly used to increase the oxidation state of carbon.

• Primary alcohols can be oxidised to aldehydes or further to carboxylic acids

This scheme summarises the oxidation sequence for a primary alcohol, showing stepwise conversion to an aldehyde and then to a carboxylic acid. It illustrates controlled oxidation as a deliberate functional group interconversion in synthesis. Source

• Secondary alcohols oxidise to ketones

• Tertiary alcohols are resistant to oxidation

Control of conditions is essential, as over-oxidation can occur if unsuitable reagents or heating are used.

Reduction Reactions

Reduction allows conversion to more reduced functional groups.

• Alkenes can be reduced to alkanes

• Aldehydes and ketones can be reduced to alcohols

Reductions are often used to reverse oxidation steps or to finalise a synthetic route.

Substitution Reactions

Substitution reactions enable functional group exchange.

• Haloalkanes can be converted into alcohols via nucleophilic substitution

• Alcohols can be converted back into haloalkanes using halide ions and acid

These reactions are useful for introducing or removing halogen atoms during synthesis.

Elimination Reactions

Elimination reactions remove small molecules to form multiple bonds.

This diagram shows an elimination reaction where a haloalkane forms an alkene under basic ethanolic conditions. The percentage yield shown is extra detail beyond OCR requirements, but the functional group change is directly relevant. Source

• Alcohols can be dehydrated to form alkenes

• Haloalkanes can undergo elimination to produce alkenes under suitable conditions

Elimination is often used to create unsaturation that can be exploited in later steps.

Planning Multi-Step Routes

Applying the toolkit requires planning multi-stage routes rather than single reactions. Students should:

• Identify the starting functional group

• Identify the target functional group

• Work stepwise, selecting known reactions to bridge the gap

Each step must be chemically realistic and based on reactions already learned.

There should always be at least one clear functional group change at each stage.

Sequencing and Compatibility

Correct sequencing matters in synthetic planning.

• Some functional groups may not survive harsh conditions

• Oxidation should not be attempted after reduction if it reverses progress

• Certain reagents may interfere with existing functional groups

Students should avoid unnecessary steps and choose the most direct route possible using known chemistry.

Using Supplied Reactions in Assessments

Examination questions may include additional reactions not previously encountered. These will always be provided with sufficient information.

• Students must integrate the new reaction into their existing toolkit

• The unfamiliar reaction should be treated as another valid transformation

• No memorisation of unfamiliar mechanisms is required

This tests adaptability rather than recall.

Applying Chemical Logic

When applying the reaction toolkit, answers should show clear chemical reasoning:

• Each step should be justified by a known transformation

• Reagents and conditions should be appropriate for the functional group

• Routes should be efficient and chemically sensible

This principle helps students track changes across multi-stage routes.

Common Pitfalls to Avoid

• Introducing reactions outside Module 4

• Skipping steps without chemical justification

• Using conditions incompatible with the functional group present

• Reversing progress by undoing previous transformations

Applying the reaction toolkit successfully requires structured thinking, familiarity with transformations, and disciplined use of the chemistry already learned.