IGCSE化学 同系物 烷烃烯烃 醇酸酯 聚合物
CAIE IGCSE 化学 0620 的第 11 章是有机化学，考纲把它拆成八个小节，从画分子式一路排到聚合物。这一章在整张卷子里占的分值不算最大，但名词密度最高，几乎每个自然段都在考定义与结构。Core 与 Extended 的界线在这里分得比较清楚，命名、酯与缩聚反应只出现在 Supplement 一栏。很多学生以为有机化学只能靠背，其实它更像一套规则系统，规则记牢之后新分子也能推出来。复习这一章时，把官网上 0620 考纲的 11.1 到 11.8 当作清单逐条打勾最省时间。下面按考纲的小节顺序，把每个考点该掌握到什么深度讲清楚。
Cambridge IGCSE Chemistry 0620 puts organic chemistry in topic 11, where eight sub-sections run from drawing displayed formulae to naming condensation polymers; the vocabulary load is higher here than anywhere else in the syllabus. Core candidates are examined on the naming of five simple compounds and on the fuels, alkanes, alkenes, alcohols and poly(ethene); the ester and condensation-polymer detail sits in the Supplement column, which only Extended candidates meet. Treat the syllabus outcomes as a checklist, because almost every mark in this topic comes from using the right name, the right functional group or the right linkage rather than from recalling long paragraphs.
同系物与功能团的定义
考纲 11.1 先要求用通式把同系物说清楚，烷烃是 CnH2n+2，烯烃是 CnH2n，醇是 CnH2n+1OH，羧酸是 CnH2n+1COOH。同系物的成员彼此相差一个 CH2，性质随碳链变长而平缓变化，不是突变。功能团是决定化学性质的那一个原子或原子团，双键、羟基与羧基都属于这一类。很多学生以为同系物就是长得像的分子，其实判据是同一个通式加同一个功能团。甲烷与乙烷同属烷烃，乙醇与丙醇同属醇，而乙醇与乙烷虽然都只有两个碳，却因为功能团不同分成两族。Extended 一栏还要求把结构式写成不含糊的形式，例如 CH3CH2OH 与 CH3COOCH3。结构异构体是分子式相同而结构式不同的化合物，考纲把它限定在 C4H10 与 C4H8 两个例子上。
A homologous series is defined by a shared general formula and a shared functional group, so alkanes, alkenes, alcohols and carboxylic acids each behave as one family with predictable trends. The Supplement column then adds structural formulae as an unambiguous description of how the atoms are arranged, and defines structural isomers as compounds with the same molecular formula but different structural formulae. Candidates who can read a formula for its functional group usually answer definition questions in a single line.
命名的两段结构：词干与后缀
11.2 的命名要求可以拆成两半，词干数碳原子，后缀说功能团。一个碳叫 meth，两个碳叫 eth，三个碳叫 prop，四个碳叫 but。烷烃用 -ane，烯烃用 -ene，醇用 -ol，羧酸用 -oic acid，酯则把 -yl 与 -oate 拼起来。Core 只要求画并命名甲烷、乙烷、乙烯、乙醇与乙酸五个分子，看到名字能说出化合物类型即可。Extended 要求不分支的烷烃、烯烃、醇与羧酸各写到四个碳，酯写到两边各四个碳。常见的错误是把酯的名字读反：来自醇的那一半在前，来自酸的那一半在后。乙酸与乙醇生成的酯叫 ethyl ethanoate，写成 CH3COOCH2CH3。
The stem counts carbon atoms and the suffix names the family, which is why propan-1-ol can be decoded without ever having seen the compound before. Esters are the case students remember best: the alkyl part comes from the alcohol and the -oate part from the acid, so ethanol with ethanoic acid gives ethyl ethanoate. Swapping the two halves produces a real compound with a different name, and that is exactly why the syllabus keeps both on the checklist.
石油分馏与馏分的性质变化
11.3 从化石燃料开始，煤、天然气与石油都要能叫出名字。天然气的主要成分是甲烷，石油是烃的混合物，而烃只含碳和氢两种元素。分馏利用的是沸点差别，越往上走碳链越短、挥发性越高、沸点越低、黏度越小。八个馏分的用途要一一对上：炼厂气用于加热与做饭，汽油用于汽车，石脑油做化工原料，煤油做航空燃料，柴油用于柴油机，燃料油用于轮船与家庭供暖，润滑油做润滑剂与蜡，沥青铺路。这一步最容易记混的是方向，塔底是沥青，塔顶是炼厂气。考纲把性质变化限定在链长、挥发性、沸点与黏度四项，不会问更细的物理数据。
Petroleum is separated by fractional distillation, and the column sorts molecules purely by boiling point, so chain length, volatility, boiling point and viscosity all change together as you move up. Every fraction carries a named use in the syllabus, from refinery gas for cooking through naphtha as a chemical feedstock to bitumen for roads. Reversing the direction of the column costs marks far more often than forgetting a single use.
烷烃：饱和与氯代反应
11.4 先说键的性质，烷烃里只有单键，所以被称为饱和烃。它们的化学性质总体不活泼，考纲只给了两条出路：燃烧，以及被氯取代。Core 要求会用甲烷举例说明这种不活泼，Extended 要求把与氯的反应写成取代反应，一次只换掉一个原子或原子团。这个反应是光化学反应，紫外线提供活化能，没有光就不发生。写成方程式时，甲烷与氯气生成氯甲烷与氯化氢，也就是 CH4 + Cl2 -> CH3Cl + HCl。很多学生以为取代反应和加成反应可以互换，其实烷烃缺少双键，加成无从谈起。
Alkanes are saturated because every carbon to carbon bond in the chain is single, which leaves them unreactive except towards oxygen in combustion and towards chlorine in a substitution reaction. That chlorination is photochemical, so ultraviolet light supplies the activation energy, and the syllabus limits the detail to monosubstitution where one hydrogen is replaced by one chlorine. Writing the product as an addition compound is the mistake that shows a student has not yet separated the two reaction types.
烯烃：裂化、溴水检验与加成反应
11.5 从结构讲起，烯烃含碳碳双键，属于不饱和烃。分馏拿到的短链烯烃不够用，工业上就用裂化把长链烷烃变成短链烷烃、烯烃和氢气，条件是高温加催化剂。裂化的原因值得单独记：短链馏分需求大，长链馏分过剩。饱和与不饱和的检验用溴水，烯烃让它褪色，烷烃保持原有的橙色。加成反应只生成一种产物，考纲列出的三个伙伴是溴或溴水、镍催化下的氢，以及酸催化下的水蒸气。三个反应都要会画产物结构，乙烯加氢得乙烷，乙烯加水得乙醇。
Cracking exists because the short-chain fractions that industry wants are scarce while the long-chain fractions are plentiful, so large alkanes are broken down over heat and a catalyst into smaller alkanes, alkenes and hydrogen. The bromine water test separates saturated from unsaturated hydrocarbons in one step, since only the double bond decolourises the orange solution. Addition across that double bond gives a single product, whether the partner is bromine, hydrogen over nickel or steam over an acid catalyst.
乙醇的两种制法与反应条件
11.6 要求同时掌握发酵与催化水合两条路线。发酵用葡萄糖水溶液，酵母在无氧条件下完成转化。温度要控制在 25 至 35 摄氏度，产物是乙醇与二氧化碳。催化水合让乙烯与蒸汽在酸催化剂存在下反应。条件是 300 摄氏度与 6000 千帕，也就是 60 个大气压。Extended 还要比较两条路线的优劣。发酵用可再生原料，设备简单，但速度慢且只能间歇生产。水合路线速度快、产品纯、可以连续运行，代价是高温高压与不可再生的乙烯。乙醇的燃烧与溶剂、燃料两个用途也在这一节里。
Ethanol can be made by fermenting aqueous glucose with yeast in the absence of oxygen at 25 to 35 degrees Celsius, or by adding steam to ethene at 300 degrees Celsius and 60 atmospheres over an acid catalyst. Fermentation runs on renewable material and needs little energy, yet it works in slow batches and gives an impure product, while hydration is fast, continuous and pure but depends on non-renewable ethene. Both routes give the same molecule, so the exam question is normally about conditions and trade-offs rather than about the reaction itself.
羧酸：弱酸性、盐的命名与反应
11.7 先处理物理性质，甲酸与乙酸都能溶于水，水溶液显酸性但只属于弱酸。它们与金属、碱、碳酸盐都能反应，考纲要求会写生成盐的名字，甲酸给出的盐叫甲酸盐，乙酸给出的叫乙酸盐。羧酸与醇在酸催化下生成酯，这个反应叫酯化。产物有甜味，常被用作香精与香水，所以酯的命名要写得准确。常见的错误是把酯化与中和混在一起，中和生成盐和水，酯化生成酯和水。弄清楚反应物里有没有醇，两条路线就不会混。
Aqueous solutions of methanoic acid and ethanoic acid turn litmus red but only partially ionise, which is what makes them weak acids rather than strong ones. They still show the full pattern of acid reactions with metals, bases and carbonates, and the salt formed takes the -oate ending that matches the acid. With an alcohol and an acid catalyst the same -COOH group forms an ester, a sweet-smelling compound used in flavourings and perfumes, and the ester name is built from both starting materials.
加聚反应与单体识别
11.8 的核心是加聚，乙烯分子里的双键打开，成千上万个单体首尾相连成聚乙烯。命名有规律可循：聚乙烯来自乙烯，聚丙烯来自丙烯，聚氯乙烯来自氯乙烯，聚四氟乙烯来自四氟乙烯。拿到聚合物的名字，去掉 poly 与括号就是单体，反过来也一样。Core 只要求聚乙烯这一例，但结构与命名的对应关系在考试里反复出现。塑料制品的处理也在这节，难降解、燃烧可能放出有毒气体、回收与再利用三条都要能写。阅卷时常见的一种答案只写聚合物很稳定，没有说清稳定与难降解之间的联系。
In addition polymerisation the double bond opens and thousands of identical monomers join end to end, so the polymer name is simply the monomer name wrapped in poly(), as in poly(ethene) from ethene and poly(chloroethene) from chloroethene. The syllabus asks for poly(ethene) by name, plus the environmental argument that these plastics break down very slowly and can release toxic gases when burned. Reading the monomer straight off the bracket is a skill that saves memory work in the exam.
缩聚反应：聚酰胺与聚酯
Extended 部分要求把缩聚讲清楚：单体各带两个功能团，每连一次就脱掉一个小分子，通常是水。二羧酸与二胺生成聚酰胺，尼龙是例子，连接处是酰胺键，写作 -CONH-。二羧酸与二醇生成聚酯，PET 是例子，连接处是酯键，写作 -COO-。蛋白质可以看作天然聚酰胺，单体是氨基酸，一端是氨基一端是羧基，脱水后形成同样的酰胺键。加聚与缩聚的差别集中在两点：单体需要几个功能团，以及生成物里有没有小分子。把 PET 水解回单体再重新聚合属于化学回收，这也是饮料瓶要单独收集的原因。
Condensation polymerisation needs monomers with a functional group at each end, and every new link costs a small molecule, normally water; a dicarboxylic acid with a diamine gives a polyamide such as nylon, while the same acid with a diol gives a polyester such as PET. Proteins are natural polyamides built from amino acids, using exactly the same -CONH- linkage that nylon uses. Because the ester linkage in PET can be hydrolysed back to its monomers, chemical recycling recovers material that addition polymers would simply lose.
溴水检验、酯化回流与实验题评分点
实验卷与替代实验卷都会回到有机化学，最常见的是溴水检验与酯化装置。溴水检验只要求观察褪色，操作描述里要有振荡与观察颜色两步。酯化装置要答出回流、水浴加热与闻气味的方法，直接对着试管口闻是错的。Paper 6 一类书面实验题还会问分馏装置里温度计水银球的位置，答案是支管口处。摄氏度与压力的写法也算细节分，压力写成 60 个大气压比只写 60 更清楚。这些细节的分数不高，却是核心内容都答对之后最容易漏掉的部分。
Practical questions on this topic usually come down to technique: shake the tube and record the colour change for the bromine test, or heat the acid and alcohol mixture under reflux in a water bath for esterification. Written alternative-to-practical papers ask where the thermometer bulb sits in a fractionating column, which is at the side arm rather than in the liquid. Marks here are small but reliable, so a candidate who has memorised the organic content still loses them without the apparatus detail.
四周推进顺序：分子式、功能团、反应、聚合物
四周的分配可以按依赖关系来。第一周只做 11.1 与 11.2，把通式、功能团与命名练到看见结构就能写名字。第二周做 11.3 与 11.4，分馏的八个馏分与烷烃的取代反应要背到能默写方程式。第三周做 11.5 与 11.6，裂化、溴水检验、加成反应与乙醇的两条路线放在一起对比。第四周留给 11.7 与 11.8，羧酸、酯化、加聚与缩聚连着写一遍，再回头做真题。每周留一次 20 分钟的自测，只默写功能团、通式与产物结构，不做计算题。
A four-week sequence works because the topic is layered: naming depends on functional groups, the reaction sections depend on the two families of hydrocarbons, and polymers depend on alkenes. Weeks one and two cover formulae, naming, fuels and alkanes, while weeks three and four pair cracking and addition reactions with alcohols before closing on carboxylic acids, esters and the two polymer mechanisms. One short weekly self-test on functional groups, general formulae and product structures keeps the vocabulary active without eating into calculation practice.
三类高频错误：命名、反应条件与产物结构
最后一节把最容易丢分的三类错误集中处理。命名类的错误集中在酯的名字顺序与后缀混用，把 -ol 与 -oic acid 弄反的情况每场都有。条件类的错误集中在发酵温度与光化学反应，25 至 35 摄氏度与紫外线这两处几乎每年都考。结构类的错误集中在羧基的两个氧原子，把 CH3COOH 写成 CH3COH 就不再是乙酸。自查的方法是拿一张白纸默写八个通式与八类反应，写不出来的那一栏就是当天的复习重点。错得最多的是酯的命名，因为它同时考了语言顺序与结构理解。
Most lost marks in this topic fall into three groups: ester names written back to front, reaction conditions such as 25 to 35 degrees Celsius for fermentation or ultraviolet light for chlorination, and structures that drop one of the two oxygen atoms in a carboxylic acid. A blank-page test is the quickest check, because writing the eight general formulae and the main reaction types from memory exposes the one column that is still shaky. Ester naming deserves the extra repetition, since it tests language order and structure at the same time.
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