Organic synthesis (A Level)
Introduced| English | Meaning |
|---|---|
| acyl chloride/əˈkɪl ˈklɔːraɪd/ | An organic compound containing a carbonyl carbon bonded to a chlorine atom and another carbon group or hydrogen. |
| functional group/ˈfʌŋkʃənl ɡruːp/ | An atom or group of atoms responsible for characteristic chemical reactions of an organic compound. |
| diazonium salt/ˌdaɪəˈzəʊnɪəm sɒlt/ | A salt containing a diazonium group in which two nitrogen atoms are bonded together and one is attached to an organic group. |
| reagent/rɪˈeɪdʒənt/ | A substance used to bring about a chemical reaction or test for another substance. |
| by-product/baɪ ˈprɒdʌkt/ | A secondary product formed alongside the main intended product of a process. |
Designing a synthesis
- Like AS synthesis, you join up known reactions to build a target.
- Now you also have the reactions of arenes, phenol, amines, amides and acyl chlorides 酰氯.
- Identify the groups, use the map, plan backwards.
A-Level synthesis planner
Build a route by matching functional-group changes to reagents.
Planning an organic synthesis means choosing a sequence of reactions to convert a starting material into a target molecule.
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Few steps and good yields are preferred.
Identifying functional groups 官能团
- decolourises bromine water with no catalyst (white precipitate) → a phenol or phenylamine (activated ring).
- reacts violently with cold water (HCl fumes) → an acyl chloride.
- purple colour with neutral $\text{FeCl}_3$ → a phenol.
A map of the A Level reactions
A purple colour with neutral iron(III) chloride identifies a:
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Neutral FeCl₃ gives a purple colour with phenols.
A compound that reacts violently with cold water, giving fumes of HCl, is a:
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Acyl chlorides hydrolyse vigorously with water, releasing HCl.
Match each term to its meaning.
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Each item links the term to its correct meaning.
The A Level reaction map
- aromatic chain: benzene → nitrobenzene → phenylamine → diazonium salt 重氮盐 → phenol / azo dye.
- acyl chain: carboxylic acid → acyl chloride → ester / amide.
- plus: amide/nitrile → amine ($\text{LiAlH}_4$); halogenoalkane → nitrile (KCN, +1 carbon).
Identification tests added at A Level
Phenylamine reacting with HNO₂ below 10 °C gives:
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Cold HNO₂ forms a diazonium salt, which can then make phenol or couple to an azo dye.
Ethanoyl chloride reacts with excess ammonia to form the amide ____.
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The acyl group stays as CH₃CO– and –NH₂ replaces –Cl, giving CH₃CONH₂.
Replacing a halogen with –CN adds one carbon to the organic molecule.
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The carbon in the cyanide group joins the carbon skeleton; count it when planning the product.
Which reagent reduces an amide to an amine?
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LiAlH₄ is the reducing agent on the reaction map. FeCl₃ and bromine water are identification tests.
Planning and analysing
- plan by working backwards from the target; write each step's reagent 试剂 and conditions.
- analyse by stating each step's reaction type (electrophilic substitution, addition–elimination, oxidation, reduction…) and watching for by-products 副产物.
Plan backwards from the target, one disconnection at a time, until you reach the starting materials
The best way to plan a multi-step synthesis is to:
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Working backwards finds which reaction makes the target, and from what, step by step.
You've got it
- tests: neutral FeCl₃ → purple (phenol); violent with cold water (acyl chloride); bromine water, no catalyst (phenol/phenylamine)
- map: benzene → nitrobenzene → phenylamine → diazonium → phenol/azo; acid → acyl chloride → ester/amide
- plan backwards from the target; analyse each step's reaction type and by-products