Organic synthesis
Cambridge A-Level Chemistry (9701) · Unit 36: Organic synthesis (A Level) · 8 flashcards
Organic synthesis is topic 36.1 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 36 — Organic synthesis (A Level) . In one line: The molecule contains a ketone (C=O) and an alkene (C=C) functional group.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 8 flashcards — 3 definitions and 5 key concepts — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Identify the functional groups present in the following molecule: CH3CH2COCH2CH=CH2
The molecule contains a ketone (C=O) and an alkene (C=C) functional group.
What the Cambridge 9701 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- for an organic molecule containing several functional groups: (a) identify organic functional groups using the reactions in the syllabus (b) predict properties and reactions
- devise multi-step synthetic routes for preparing organic molecules using the reactions in the syllabus
- analyse a given synthetic route in terms of type of reaction and reagents used for each step of it, and possible by-products
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Organic synthesis
- › Sequence reactions carefully based on directing groups; -COOH is 3-directing, while -CH3 is 2,4-directing.
- › Work backwards: a hydroxynitrile is formed by nucleophilic addition of HCN to an aldehyde, which is formed by mild oxidation of a primary alcohol.
Identify the functional groups present in the following molecule: CH3CH2COCH2CH=CH2
The molecule contains a ketone (C=O) and an alkene (C=C) functional group.
Name the reagents and conditions required to reduce a carboxylic acid to a primary alcohol.
The reagent required is Lithium Aluminium Hydride (LiAlH₄) in dry ether, followed by aqueous acid workup. This reduction is stronger than using NaBH₄.
Outline a multi-step synthetic route to convert ethanol to butanoic acid.
Step 1: Oxidation of ethanol to ethanal using acidified potassium dichromate(VI), distilled immediately. Step 2: Oxidation of ethanal to ethanoic acid, under reflux. Step 3: React ethanoic acid with PCl5 to make ethanoyl chloride. Step 4: React ethanoyl chloride with ethyl magnesium bromide. Step 5: Hydrolyse the product with dilute acid to form butan-2-ol. Step 6: Oxidise butan-2-ol using acidified potassium dichromate(VI), distilled immediately to form butanone. Step 7: Oxidise butanone to butanoic acid using acidified potassium dichromate(VI), under reflux.
What type of reaction is involved in converting an alcohol to an alkene using concentrated sulfuric acid?
This is an elimination reaction, specifically dehydration. The sulfuric acid acts as a dehydrating agent, removing water from the alcohol to form the alkene.
What reagents are required to convert a primary alcohol to an aldehyde?
Acidified Potassium Dichromate(VI) (K₂Cr₂O₇ / H⁺) with distillation to remove the aldehyde as it forms, preventing further oxidation to a carboxylic acid.
Identify the possible by-product(s) when reacting ethanol with excess concentrated sulfuric acid at 170°C.
The main organic by-product is diethyl ether, formed via intermolecular dehydration. Water is also produced. Polymerisation of ethene to form longer chain alkenes is another, minor possibility.
Describe the purpose of reflux in a chemical reaction.
Reflux allows a reaction to be heated at its boiling point for an extended period without loss of volatile reactants or products. This increases the reaction rate and yield.
Suggest a suitable reagent for converting a ketone to a secondary alcohol.
Sodium borohydride (NaBH₄) in ethanol is a suitable reducing agent. Alternatively, Lithium Aluminium Hydride (LiAlH₄) can be used, followed by dilute acid, but this is a stronger reducing agent and requires anhydrous conditions.
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