Edexcel A-Level 有机化学高效备考规划 | Edexcel A-Level Organic Chemistry: Efficient Revision Plan

Edexcel A-Level 有机化学高效备考规划

Organic Chemistry is the largest and most heavily-weighted topic in Edexcel A-Level Chemistry -- spanning Topics 6, 17, and 18 across both AS and A2. With roughly 30-35% of exam marks coming from organic, mastering this domain is non-negotiable for a top grade. 有机化学是Edexcel A-Level化学中占比最大的部分，横跨Topic 6（AS）、17和18（A2），占据约30-35%的考试分值。有机化学的考题类型涵盖命名题、机理题、合成路线设计题、波谱解析题和实验操作题。无论目标是拿下A*还是夯实化学基础，有机化学都是你必须攻克的制高点。拿下有机化学，是冲击A*的必经之路。This article maps out an efficient 8-week revision plan that moves systematically from fundamentals to complex multi-step synthesis, with exam-tested strategies at every stage. 本文按8周规划梳理Edexcel有機化学的完整知识体系，从最基础的命名和异构开始，逐步推进到多步合成和波谱解析，每一阶段都配有Edexcel真题中最常见的考试策略和高频易错点。

Week 1-2: Foundation -- Nomenclature, Isomerism and Functional Groups | 基础阶段 -- 命名、异构与官能团

Everything in organic chemistry builds on your ability to name compounds correctly and recognise functional groups instantly. 有机物命名是贯穿始终的基础技能。先掌握IUPAC命名法：找最长碳链定母体名称→编号定位取代基→根据官能团优先顺序确定后缀。Start by mastering IUPAC nomenclature: identify the longest carbon chain (parent name), locate and number substituents, and apply suffix/prefix rules for functional groups. Pay special attention to priority order -- carboxylic acid > ester > acyl chloride > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > halogenoalkane. Edexcel喜欢考察的陷阱包括：环状化合物编号起点选择、含双键和羟基时编号优先级冲突、以及E/Z异构体的命名。很多同学在命名题丢分是因为忘记官能团优先顺序 -- -- 比如同时含有羟基和双键时，羟基优先级更高，母体以-ol结尾，双键作为"en"插入，编号要优先给羟基。

Then tackle isomerism -- structural (chain, position, functional group) and stereoisomerism (E/Z, optical). For E/Z, remember the Cahn-Ingold-Prelog priority rules and that E = "opposite sides" (entgegen), Z = "same side" (zusammen). Optical isomerism requires a chiral carbon (four different groups attached) and the ability to draw 3D tetrahedral arrangements with wedged/dashed bonds. 同分异构体是高频考点。结构异构包括碳链异构、位置异构、官能团异构；立体异构考E/Z和光学异构。E/Z用Cahn-Ingold-Prelog原子序数规则判断优先级，Z是same side（同侧），E是opposite sides（异侧）。光学异构必须有手性碳 -- -- 连接四个不同基团 -- -- 会画楔形/虚线3D结构并标出对映体。Practice drawing both enantiomers and identifying racemic mixtures. 做真题时注意：数同分异构体时很容易漏掉官能团异构 -- -- 比如分子式C₃H₆O，既有丙醛也有丙酮；C₄H₁₀O既有醇也有醚。另外，外消旋体（racemic mixture）是等量两种对映体的混合物，没有光学活性，这个概念Edexcel非常喜欢考。

Functional group recognition drill: Create flashcards for all 12+ functional groups tested (alkene, halogenoalkane, alcohol, aldehyde, ketone, carboxylic acid, ester, acyl chloride, amide, amine, nitrile, arene). For each, know the general formula, suffix/prefix, and characteristic IR absorption. 把所有常考官能团做成闪卡：烯烃、卤代烷、醇、醛、酮、羧酸、酯、酰氯、酰胺、胺、腈、芳烃。每个要记住通式、命名后缀/前缀和特征红外吸收。例如，醛的特征是C=O在1720-1740 cm⁻¹和C-H（醛基）在2720-2820 cm⁻¹的双峰组合，这是IR题中区分醛和酮的经典标志。前两周把这些基础打牢，后面六周的机理和合成才能建立起直觉。

Week 3: Alkanes and Alkenes -- The Hydrocarbon Backbone | 烷烃与烯烃 -- 碳氢骨架

Alkanes are chemically relatively inert, but their reactions -- combustion (complete/incomplete) and free radical substitution with halogens -- are the foundation for understanding reaction mechanisms. 烷烃的核心反应是自由基取代。三步机理必须能默写：引发（UV光断裂Cl-Cl键生成两个Cl•）、链增长（Cl•夺H生成•CH₃和HCl、•CH₃再与Cl₂反应生成CH₃Cl和新的Cl•）、链终止（两个自由基结合 -- -- Cl•+Cl•→Cl₂，•CH₃+Cl•→CH₃Cl，•CH₃+•CH₃→C₂H₆）。考试常问：为什么产物是多取代混合物？如何通过控制Cl₂用量影响产率？答：因为链增长反应中Cl•的攻击是随机的，会逐步取代多个H原子。控制Cl₂用量使甲烷大大过量，可提高一氯甲烷的产率。

Alkenes are far more reactive due to the electron-rich π-bond. 烯烃的亲电加成是必考机理。Master electrophilic addition across the C=C double bond with these reagents and conditions: H₂ (Ni catalyst, 150°C) → alkane; HX (room temp) → halogenoalkane; X₂ (room temp) → dihalogenoalkane; H₂SO₄ then H₂O (cold concentrated H₂SO₄ then warm water) → alcohol. 掌握四种试剂：H₂/Ni→烷烃、HX→卤代烷、X₂→二卤代烷、H₂SO₄/H₂O→醇。For unsymmetrical alkenes, apply Markovnikov's rule: the hydrogen adds to the carbon with more hydrogens already attached (the electrophile Hδ+ attacks the C with greater electron density). 不对称烯烃必须用马氏规则判断主产物 -- -- H加在氢多的碳上。还要会写碳正离子中间体，理解为什么tertiary carbocation最稳定（烷基供电诱导效应+超共轭）。考试中需要画出curly arrow从双键出发到H⁺，生成碳正离子，然后X⁻进攻碳正离子。每一步箭头必须从电子对或键出发，指向被进攻的原子。

Addition polymerisation: Be able to draw the repeat unit of poly(ethene), poly(propene), poly(chloroethene)/PVC, and PTFE. Practice identifying the monomer from a polymer structure and vice versa. 加聚反应：会画重复单元即可。聚合物的单体和重复单元互相推导是常考题型。Edexcel还会涉及塑料的环境问题：不可生物降解、焚烧vs填埋vs回收的利弊对比。焚烧释放CO₂和有毒气体（PVC产生HCl），填埋占用土地且不分解，回收是理想方案但分拣成本高。增塑剂（plasticisers）的作用是嵌入聚合物链间减少分子间力，使塑料更柔韧。

Week 4: Halogenoalkanes -- Nucleophilic Substitution and Elimination | 卤代烷 -- 亲核取代与消去

Halogenoalkanes are the workhorse intermediates of organic synthesis. Two competing mechanisms dominate. 卤代烷中的C-X键极性决定了它的反应性 -- -- 碳带δ+，是亲核试剂的攻击位点。卤代烷之所以在有机合成中如此重要，是因为卤素是一个优良的离去基团，可以被多种亲核试剂替换，从而实现官能团转化。

Nucleophilic substitution: The halogen is replaced by a nucleophile. 亲核取代两大机理SN1和SN2必须区分清楚。SN1分两步，生成碳正离子中间体，三级卤代烷最快（三级碳正离子最稳定）；速率只取决于卤代烷浓度，rate = k[RX]。SN2是一步协同，过渡态中亲核试剂从背面进攻，一级卤代烷最快（位阻最小）；速率取决于卤代烷和亲核试剂两者浓度，rate = k[RX][Nu⁻]。常用亲核试剂：OH⁻（NaOH(aq)回流→制醇）、CN⁻（KCN/乙醇回流→制腈，碳链延长1个C，这是合成中的重要链增长方法）、NH₃过量（乙醇溶剂、密封管加压加热→制胺）。每一条转化路径的试剂和条件都必须精确记忆 -- -- 比如CN⁻用的是KCN的乙醇溶液回流，不是水溶液，因为水会导致卤代烷溶解度差且存在竞争水解。

Elimination: With hot ethanolic KOH, halogenoalkanes eliminate to form alkenes. This is a one-step E2 mechanism where the base removes H⁺ from a β-carbon while the halide leaves. 消去反应用热的KOH乙醇溶液，生成烯烃。E2机理一步完成 -- -- 碱夺β-H的同时卤素离去。Zaitsev's rule（查依采夫规则）：主产物是取代基更多的（更稳定的）烯烃。需要注意的是，取代和消去是一对竞争反应：NaOH(aq)偏向取代，NaOH(ethanolic)且加热偏向消去；一级卤代烷偏向取代，三级卤代烷偏向消去。这个条件vs产物的判断是Edexcel选择题的常客。

Rate experiments: 用AgNO₃/乙醇测水解速率是经典实验题。Edexcel loves to test the hydrolysis rates of primary, secondary, and tertiary halogenoalkanes with AgNO₃ in ethanol. Tertiary gives an immediate precipitate of AgX, secondary takes minutes, primary requires heating. 三级卤代烷立即生成AgX沉淀，二级需数分钟，一级需加热。本质是碳正离子稳定性顺序。实验中使用乙醇溶剂的原因：卤代烷在水中的溶解度低，乙醇可溶解卤代烷且能与水混溶。生成的沉淀颜色：AgCl白色、AgBr奶油色、AgI黄色，这本身又是卤素离子的鉴别方法。

Week 5: Alcohols -- Oxidation, Dehydration and Beyond | 醇 -- 氧化、消去与衍生

Alcohols sit at the crossroads of organic synthesis -- they can be made from alkenes (hydration) and halogenoalkanes (hydrolysis), and they can be transformed into aldehydes, ketones, carboxylic acids, alkenes, esters, and halogenoalkanes. 醇是有机合成的枢纽。从烯烃水合或卤代烷水解都能制备醇，而醇又能氧化成醛/酮/羧酸、消去成烯烃、酯化成酯、取代成卤代烷。理解醇的化学，等于掌握了至少六条重要的合成路线。

Oxidation ladder: Primary alcohol + K₂Cr₂O₇/H₂SO₄ → (distill immediately) → aldehyde → (reflux with excess oxidising agent) → carboxylic acid. Secondary alcohol → (reflux) → ketone (no further oxidation). Tertiary alcohol → no reaction under these conditions. 氧化阶梯是核心考点：一级醇用酸性重铬酸钾K₂Cr₂O₇/H₂SO₄，边生成边蒸馏得醛，回流过量氧化剂得羧酸。这里的技术细节很重要：为什么蒸馏能得到醛？因为醛的沸点低于羧酸，刚生成就被蒸出，避免了继续氧化。二级醇回流得酮，无法继续氧化。三级醇在酸性重铬酸钾条件下不反应 -- -- 因为它没有连接在含氢碳上的羟基，无法形成C=O。观察颜色变化：Cr₂O₇²⁻（橙色）→ Cr³⁺（绿色），是氧化发生的标志。这个颜色变化在历年真题中反复出现。

Elimination (dehydration): Alcohol + concentrated H₂SO₄ or hot Al₂O₃ → alkene + H₂O. Again, Zaitsev's rule applies. 消去脱水用浓硫酸（加热至170°C）或热Al₂O₃催化剂（300°C，通过催化剂床层），生成烯烃。Al₂O₃催化的优势在于产物纯净、无碳化副反应。温度控制是关键 -- -- 如果乙醇和浓硫酸只加热到140°C，产物不是乙烯而是乙醚（分子间脱水），这是经典陷阱题。

Esterification: Alcohol + carboxylic acid ⇌ ester + H₂O (concentrated H₂SO₄ catalyst, reflux). 酯化是可逆反应，浓硫酸催化+回流，加过量反应物或移除水有利于正向。This is a reversible equilibrium -- use excess of one reactant or remove water to drive it forward. Naming esters: the alcohol part gives the alkyl prefix, the acid part gives the alkanoate suffix (e.g., ethanol + ethanoic acid → ethyl ethanoate，中文：乙醇+乙酸→乙酸乙酯)。Edexcel还常考酯的用途：作溶剂（低毒、挥发性适中）、作香料和调味剂（水果气味）、作增塑剂。酯的制备实验中通常加入沸石防暴沸，并用饱和Na₂CO₃溶液洗涤产物以除去未反应的酸。

Week 6: Carbonyls -- Aldehydes, Ketones and Distinguishing Tests | 羰基化合物 -- 醛酮与鉴别

Carbonyl chemistry revolves around the polar C=O bond and nucleophilic addition. The key distinction between aldehydes and ketones is that aldehydes can be further oxidised to carboxylic acids while ketones cannot -- this is the basis of nearly every distinguishing test. 醛和酮的核心区别在于醛能继续被氧化，酮不能 -- -- 所有鉴别实验都基于这一点。羰基中碳氧双键的极性（氧电负性大于碳，碳带δ+）是亲核加成的驱动力，所有羰基反应都源于此。

Nucleophilic addition with HCN: Aldehydes and ketones both react with HCN (generated in situ from KCN + dilute H₂SO₄) to form hydroxynitriles. HCN亲核加成延长碳链：醛/酮 + KCN/稀H₂SO₄ → 羟基腈（cyanohydrin）。This is a key chain-lengthening reaction -- the CN group can be hydrolysed to a carboxylic acid or reduced to an amine. CN基可水解成羧酸或还原成胺 -- -- 这条路线可以实现醛/酮→羟基腈→羟基羧酸，碳链延长1个C。必须说明为什么用KCN+H₂SO₄而不是直接用HCN -- -- 因为HCN是剧毒气体（沸点26°C，常温为气体），实验室使用太危险，所以现场用KCN加酸少量生成。

Reduction with NaBH₄: Aldehydes → primary alcohols; Ketones → secondary alcohols. 硼氢化钠NaBH₄还原：NaBH₄提供H⁻（氢负离子）作为亲核试剂，进攻羰基的δ+碳。NaBH₄的水溶液或醇溶液在室温条件下即可完成还原。对比催化加氢（H₂/Ni），NaBH₄更温和、选择性更好 -- -- 它只还原C=O，不还原C=C。这意味着从α,β-不饱和醛酮出发，可以只还原羰基而保留双键，这在合成中非常有价值。

2,4-DNP (Brady's reagent): Both aldehydes and ketones give an orange-yellow precipitate of the 2,4-dinitrophenylhydrazone derivative. 2,4-DNP是羰基的广谱检测试剂，醛酮都能生成橙黄色沉淀，但不能区分二者。衍生物有明确的熔点，通过测熔点并与文献值对照可以鉴定具体的醛或酮 -- -- 这在实验中是经典方法。

Distinguishing tests -- 三大鉴别实验：Tollens' reagent (ammoniacal silver nitrate [Ag(NH₃)₂]⁺) -- aldehyde gives a silver mirror, ketone no reaction. Fehling's or Benedict's solution (alkaline Cu²⁺ complex) -- aldehyde gives a brick-red precipitate of Cu₂O, ketone no reaction. Acidified potassium dichromate -- aldehyde turns from orange to green (Cr³⁺), ketone no reaction. 三大鉴别实验的原理务必理解：Tollens试剂利用Ag⁺被醛还原为Ag(0)形成银镜；Fehling/Benedict利用Cu²⁺被还原为Cu₂O砖红色沉淀；酸化的重铬酸钾利用Cr⁶⁺（橙色）被还原为Cr³⁺（绿色）。三种实验本质上都在检测醛的还原性 -- -- 醛可以被温和氧化剂氧化，酮不可以。实验题中，如果问"如何鉴别一瓶未知液体是醛还是酮"，优先选用Tollens试剂，因为结果最直观（银镜或没有）。

Week 7: Carboxylic Acids, Esters, Acyl Chlorides and Amides | 羧酸衍生物 -- 活性顺序与转化

This group forms an integrated reaction network where reactivity decreases in the order: acyl chloride > carboxylic acid > ester > amide. Understanding this reactivity gradient lets you predict which transformations are feasible and which require different reagents. 羧酸衍生物的活性顺序：酰氯 > 羧酸 > 酯 > 酰胺。理解这个顺序，就能判断哪些转换可以直接实现，哪些需要更剧烈的条件或间接路线。活性差异的根本原因在于离去基团的碱性：Cl⁻是最弱的碱、最好的离去基团，所以酰氯最活泼；NH₂⁻是强碱、最差的离去基团，所以酰胺最稳定。

Acyl chlorides (RCOCl) are the most reactive acid derivatives and react vigorously at room temperature with water (→ carboxylic acid + HCl), alcohols (→ ester + HCl), ammonia (→ amide + HCl), and primary amines (→ N-substituted amide + HCl). 酰氯的反应活性最高，室温即可与水、醇、氨、胺发生亲核加成-消去反应。产物分别对应羧酸、酯、酰胺和N-取代酰胺，同时生成HCl白雾（steamy white fumes of HCl）。These are all nucleophilic addition-elimination reactions -- the nucleophile adds to the carbonyl carbon, the Cl leaves as the leaving group, and the tetrahedral intermediate collapses to reform C=O. 机理通用模板：Nu⁻进攻羰基碳→四面体中间体→Cl⁻离去→C=O重新生成。每一步必须画curly arrow。

Esters are less reactive and require heating with acid or base catalyst. Acid hydrolysis (dilute HCl, reflux) regenerates the parent carboxylic acid and alcohol (equilibrium). Base hydrolysis (NaOH, reflux) produces the carboxylate salt and alcohol -- this goes to completion because the carboxylate cannot re-esterify. 酯的水解：酸催化（稀HCl回流）是可逆的，得回羧酸+醇；碱催化（NaOH回流）不可逆，生成羧酸盐+醇。碱水解也称为皂化反应（saponification） -- -- 为什么叫皂化？因为动植物油脂（甘油三酯）的碱水解产物就是肥皂（脂肪酸钠盐）+甘油。

Polyesters and polyamides: Know the condensation polymerisation between a diol + dicarboxylic acid (→ polyester) and diamine + dicarboxylic acid (→ polyamide). 缩聚反应：二醇+二酸→聚酯+水；二胺+二酸→聚酰胺+水。Be able to draw repeat units and identify monomers from polymer structures. Kevlar（凯夫拉防弹纤维，由1,4-二氨基苯+对苯二甲酰氯缩聚）和nylon-6,6（尼龙-66，由己二胺+己二酸缩聚）是经典例子。从聚合物结构反推单体时，对于聚酯找到酯键(-COO-)切断，加H₂O得到醇和酸；对于聚酰胺找到酰胺键(-CONH-)切断，加H₂O得到胺和酸。注意区分加聚和缩聚：加聚只有C=C单体，没有小分子副产物；缩聚有两种官能团单体，有小分子（通常是水或HCl）副产物。

Week 8: Spectroscopy and Multi-Step Synthesis | 波谱解析与多步合成 -- 综合冲刺

Infrared (IR) spectroscopy: 红外光谱记住几个关键吸收峰：O-H（醇/酚，3200-3550 cm⁻¹，宽峰broad）、O-H（羧酸，2500-3300 cm⁻¹，非常宽very broad）、C=O（1680-1750 cm⁻¹，尖强峰sharp/strong）、C-O（1000-1300 cm⁻¹）、N-H（3300-3500 cm⁻¹，中强峰）。Edexcel data booklet provides exact values -- your job is to identify which functional groups are present by matching peaks to the table. 考试会提供Data Booklet中的IR吸收表，你的任务是匹配峰位到官能团。IR解析的步骤：先看1700附近有没有强尖峰 -- -- 有就是含羰基的化合物（醛/酮/酸/酯/酰胺） -- -- 再看其他辅证峰来细分。还有一个经典考点：指纹区（fingerprint region, <1500 cm⁻¹）是分子的"指纹"，可以用来鉴定具体化合物 -- -- 但不需要解释这个区域的每个峰。

Mass spectrometry: The molecular ion peak (M⁺) gives the relative molecular mass. 质谱中分子离子峰M⁺给出相对分子质量。Fragment peaks help deduce the structure -- common losses include CH₃ (M-15), OH (M-17), C₂H₅ (M-29), COOH (M-45). 碎片峰用于反推结构 -- -- 常见失去的碎片：CH₃(M-15)、OH(M-17)、C₂H₅(M-29)、COOH(M-45)。现代Edexcel考试更多考查高分辨质谱（high resolution mass spectrometry），可以根据精确质量确定分子式，这是区别于传统质谱的一个重要升级。

Multi-step synthesis: This is where everything comes together. Edexcel questions often give a starting material and a target molecule with 3-4 synthetic steps. 多步合成是全卷最难的大题。方法：从目标分子逆推（retrosynthesis） -- -- 要引入什么官能团→上一步中间体应该是什么→一直推到起始物。Your approach: work backwards from the target. Identify what functional group transformations are needed, what the immediate precursor could be, and trace back to the starting material. For each step, specify reagents, conditions, and any necessary purification or separation. 每一步写出试剂、条件、分离纯化方法。常见串联路线：烯烃+HBr→卤代烷+KCN→腈+HCl/H₂O回流→羧酸（链增长+官能团转化一气呵成）；醇+K₂Cr₂O₇/H₂SO₄蒸馏→醛+NaBH₄→醇（氧化再还原看似无意义，但可用于官能团保护）。

Grignard reagents: RMgX are powerful nucleophiles that react with carbonyls to form alcohols with an extended carbon skeleton. 格氏试剂是构建碳骨架的神器。With methanal → primary alcohol (1 carbon added), with other aldehydes → secondary alcohol, with ketones → tertiary alcohol, with CO₂ → carboxylic acid. 与甲醛→一级醇（加1个C）、与其他醛→二级醇、与酮→三级醇、与CO₂→羧酸。格氏试剂的制备条件：无水乙醚（dry ether）中，卤代烷+镁屑回流。必须无水 -- -- 因为格氏试剂遇水立即分解：RMgX + H₂O → RH + Mg(OH)X。这是实验题中的经典"为什么"问题。格氏试剂与CO₂的反应可以一步将卤代烷转化为多一个碳的羧酸，是非常高效的合成方法。

Exam Technique and Common Pitfalls | 考试技巧与高频失分点

Based on examiner reports, here are the most common mistakes in Edexcel A-Level Organic Chemistry and how to avoid them. 根据历年考官报告，以下是有机化学考试中最常见的失分点及应对策略。

Mechanism drawings -- 画机理箭头的常见错误：Always show curly arrows starting from a bond or lone pair, pointing to the atom being attacked. 箭头起点必须从电子对或键出发，终点指向被进攻的原子。For each arrow, ask yourself: "Where do the electrons come from, and where do they go?" Don't use "half-headed" fishhook arrows for heterolytic mechanisms -- those are only for homolytic (radical) processes. 半箭头（fishhook）只用于均裂/自由基反应，异裂机理必须用全箭头。每个箭头画完问自己：电子从哪里来，到哪里去？

Reagents and conditions -- 试剂和条件必须精确：Edexcel is strict about these. "NaOH" is not enough -- you must specify "NaOH(aq)" for hydrolysis vs "NaOH(ethanolic)" for elimination. NaOH要写明是(aq)还是(ethanolic)；"H₂SO₄" must be "concentrated H₂SO₄" or "dilute H₂SO₄" as appropriate. H₂SO₄写明浓/稀；Temperature: "reflux" vs "room temperature" vs specific temperatures like "150°C" or "170°C" matters. 温度区分回流、室温和具体度数。少写一个条件可能丢1-2分。

Naming precision -- 命名不要省略编号："2-methylpropane" not "methylpropane". "3-bromopentane" not "bromopentane". 即使看似唯一的取代位置也要标出编号。Numbering matters even when it seems obvious. 写E/Z时标注每个双键碳上优先级高的基团 -- -- Edexcel阅卷时要求明确写出"higher priority groups are on opposite/same sides"，不能只写E/Z字母。

Isomer counting -- 数同分异构体不要忘记官能团异构：When asked to draw all structural isomers of C₄H₁₀O, don't forget the ethers alongside the alcohols. Always check: have I considered functional group isomers? 比如C₄H₁₀O既有四种醇也有三种醚；C₃H₆O既有丙醛也有丙酮。另外，光学异构的计数也很容易出错 -- -- 如果分子有一个手性中心且没有内消旋面，那就是一对对映体（计为两个异构体）。

Observation questions -- 现象题不要只写方程式："State what you would observe" means describe colour changes, precipitate formation, effervescence, or smell. 描述颜色变化、沉淀生成、气泡产生或气味。Don't just write the chemical equation. E.g., "the orange solution turns green" for dichromate reduction. 例如，酸性重铬酸钾氧化一级醇的现象："the orange solution turns green and the smell of the alcohol disappears, replaced by the pungent smell of the aldehyde/carboxylic acid" -- -- 描述颜色变化、气味变化，而不是只写方程式。

Time management -- 时间管理：有机合成大题通常放在试卷后半部分，每题8-12分，不要在前面选择题耗费过多时间。按照Edexcel Paper 2的节奏：选择题30分钟→简答题50分钟→合成大题40分钟。如果遇到不会的机理，先跳过，最后回来做 -- -- 很多同学在一个机理箭头上纠结10分钟，导致后面送分题没时间写。

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