📚 Organic Synthesis: Routes, Conditions and Green Chemistry | 有机合成：路线、条件与绿色化学
Organic synthesis is a core A-level chemistry topic that tests your ability to link reagents, conditions and functional group changes into a logical multi-step route. AQA Paper 2 and Paper 3 questions frequently ask you to design a route from a starting molecule to a target molecule, justify conditions and evaluate yield or atom economy.
有机合成是 A-level 化学的核心主题，考查你是否能将试剂、条件和官能团变化串联成合理的多步路线。AQA 卷二和卷三常要求你设计从起始物到目标分子的路线，并说明反应条件、评价产率或原子经济性。
1. What is Organic Synthesis? | 什么是有机合成？
Organic synthesis is the construction of target organic molecules from simpler starting materials through a planned sequence of chemical reactions.
有机合成是通过一系列有计划的化学反应，从较简单的起始原料构建目标有机分子的过程。
At A-level, synthesis routes usually involve no more than three to five steps, and every step must change a functional group or extend a carbon chain.
在 A-level 中，合成路线通常不超过三到五步，每一步都必须改变一个官能团或延长碳链。
You should be able to describe both the 'forward' route from starting material to product and the retrosynthetic route from product back to starting material.
你应当既能描述从起始物到产物的“正向”路线，也能描述从产物回到起始物的逆合成路线。
2. Functional Group Interconversions | 官能团转化
Most AQA synthesis questions rely on interconverting common functional groups: alkenes, alcohols, halogenoalkanes, aldehydes, ketones, carboxylic acids, esters, amines and nitriles.
大多数 AQA 合成题都依赖常见官能团的相互转化：烯烃、醇、卤代烷、醛、酮、羧酸、酯、胺和腈。
For example, an alkene can be converted to an alcohol by acid-catalysed hydration with steam and H₃PO₄ catalyst, or to a halogenoalkane by electrophilic addition of HX.
例如，烯烃可通过水蒸气与 H₃PO₄ 催化剂的酸催化水合转化为醇，或通过 HX 的亲电加成转化为卤代烷。
- Alkene → alcohol: steam, H₃PO₄ catalyst, high temperature and pressure.
烯烃 → 醇：水蒸气、H₃PO₄ 催化剂、高温高压。 - Alcohol → halogenoalkane: NaBr with H₂SO₄ or PCl₅; tertiary alcohols react faster.
醇 → 卤代烷：NaBr 与 H₂SO₄ 或 PCl₅；叔醇反应更快。 - Halogenoalkane → nitrile: KCN in ethanol, heating under reflux.
卤代烷 → 腈：KCN 乙醇溶液，回流加热。
3. Key Reagents and Conditions | 关键试剂与条件
AQA expects precise recall of reagents, solvents, temperature and reflux versus distillation conditions.
AQA 要求准确记忆试剂、溶剂、温度以及回流与蒸馏条件。
Using 'dilute acid' where 'concentrated H₂SO₄' is required, or omitting 'under reflux', costs marks even if the organic transformation is correct.
在需要“浓 H₂SO₄”时写“稀酸”，或漏写“回流”，即使有机转化正确也会失分。
| Transformation 转化 | Reagent and conditions 试剂与条件 |
|---|---|
| Alkene → alkane 烯烃 → 烷烃 | H₂, Ni catalyst, room temperature and pressure H₂、Ni 催化剂，常温常压 |
| Primary alcohol → aldehyde 伯醇 → 醛 | K₂Cr₂O₇/H₂SO₄, distillation K₂Cr₂O₇/H₂SO₄，蒸馏 |
| Primary alcohol → carboxylic acid 伯醇 → 羧酸 | K₂Cr₂O₇/H₂SO₄, heating under reflux K₂Cr₂O₇/H₂SO₄，回流加热 |
| Secondary alcohol → ketone 仲醇 → 酮 | K₂Cr₂O₇/H₂SO₄, heating under reflux K₂Cr₂O₇/H₂SO₄，回流加热 |
| Halogenoalkane → amine 卤代烷 → 胺 | Excess NH₃ in ethanol, heat under pressure 过量 NH₃ 乙醇溶液，加压加热 |
Remember that oxidation of a primary alcohol gives an aldehyde only if the aldehyde is distilled off immediately; under reflux it is oxidised further to the carboxylic acid.
请记住，伯醇氧化只有在立即蒸出醛的情况下才得到醛；在回流条件下，醛会继续被氧化为羧酸。
4. Building Carbon Skeletons: Nitriles and Grignard Routes | 构建碳骨架：腈与格氏试剂路线
To increase chain length, AQA uses two main strategies: nucleophilic substitution of a halogenoalkane with KCN, and the reaction of a carbonyl compound with HCN or a Grignard reagent.
为了增长碳链，AQA 使用两种主要策略：卤代烷与 KCN 的亲核取代，以及羰基化合物与 HCN 或格氏试剂的反应。
Heating a halogenoalkane with KCN in ethanol produces a nitrile; acid hydrolysis of the nitrile then gives a carboxylic acid with one extra carbon atom.
卤代烷与 KCN 的乙醇溶液加热生成腈；腈经酸性水解得到多一个碳原子的羧酸。
Grignard reagents, RMgX, are not required in full mechanistic detail by all AQA specifications, but you should know that they add to carbonyl compounds to form alcohols after acid work-up.
并非所有 AQA 考试大纲都要求格氏试剂的完整机理，但你应知道 RMgX 与羰基化合物加成，经酸性后处理生成醇。
In exam answers, the KCN route is usually the safer A-level route when the question asks for a chain extension of one carbon.
在考试答案中，当题目要求延长一个碳链时，KCN 路线通常是更稳妥的 A-level 路线。
5. Multi-step Synthesis Planning | 多步合成路线设计
A typical AQA question provides a starting material and a target molecule, then asks you to write a three-step or four-step synthesis.
典型的 AQA 题目会给出起始原料和目标分子，然后要求你写出三步或四步合成。
Work step by step: identify the functional group in the starting material, identify the functional group in the product, and choose the shortest reliable route between them.
逐步处理：识别起始物中的官能团，识别产物中的官能团，然后选择两者之间最短且可靠的路线。
Avoid unnecessary functional group changes that could introduce side products or lower yield.
避免不必要的官能团改变，以免引入副产物或降低产率。
Always state the reagent, solvent and condition for each step, even if the question shows a reaction scheme with empty boxes.
即使题目用空框表示反应流程，每一步也要写出试剂、溶剂和条件。
6. Retrosynthesis: Working Backwards | 逆合成分析：逆向推理
Retrosynthesis means starting with the target molecule and breaking it into simpler building blocks, repeating the process until you reach the given starting material.
逆合成分析是指从目标分子出发，将其拆分为更简单的结构单元，重复这一过程直到与给定的起始原料相遇。
The key skill is to recognise 'disconnection points' at ester, amide, ether or nitrile linkages because these often correspond to known condensation or substitution reactions.
关键技能是识别酯、酰胺、醚或腈连接处的“切断点”，因为这些位置通常对应已知的缩合或取代反应。
For example, an ester can be disconnected to a carboxylic
Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图