📚 IB Chemistry: Core Organic Chemistry Knowledge | IB化学：有机化学核心知识
Organic chemistry is the study of carbon-containing compounds and their reactions. It is central to the IB Chemistry syllabus, appearing across both SL and HL papers, and requires a firm grasp of structure, reactivity, and analysis.
有机化学是研究含碳化合物及其反应的学科。它是IB化学课程的核心内容，在标准级（SL）和高级级（HL）考试中都会出现，要求掌握结构、反应性和分析的基本概念。
1. Functional Groups and Naming | 官能团与命名
A functional group is the reactive part of a molecule that gives it characteristic properties. Common ones include alkenes (C=C), alcohols (–OH), aldehydes (–CHO), ketones (–C=O), carboxylic acids (–COOH), esters (–COO–), amines (–NH₂), and amides (–CONH–).
官能团是分子中具有特征反应性的部分。常见的官能团包括烯烃（C=C）、醇（–OH）、醛（–CHO）、酮（–C=O）、羧酸（–COOH）、酯（–COO–）、胺（–NH₂）和酰胺（–CONH–）。
IUPAC naming uses a root from the longest carbon chain, a suffix for the principal functional group, and numbers/prefixes for substituents. For example, CH₃CH₂CH₂OH is propan-1-ol; CH₃CH₂COOH is propanoic acid.
IUPAC命名法选取最长碳链作为主链，用后缀表示主要官能团，并用编号和前缀表示取代基。例如，CH₃CH₂CH₂OH 是丙-1-醇；CH₃CH₂COOH 是丙酸。
2. Isomerism | 同分异构
Isomers are molecules with the same molecular formula but different structures. They can be classified as structural (constitutional) or stereoisomers.
同分异构体是具有相同分子式但结构不同的分子。它们可分为结构异构体和立体异构体。
Structural isomerism includes chain isomerism (e.g. butane and 2-methylpropane), position isomerism (e.g. butan-1-ol and butan-2-ol), and functional group isomerism (e.g. propanal and propanone).
结构异构包括碳链异构（如丁烷和2-甲基丙烷）、位置异构（如丁-1-醇和丁-2-醇）以及官能团异构（如丙醛和丙酮）。
Stereoisomerism includes E/Z (cis-trans) isomerism in alkenes, and optical isomerism where an asymmetric carbon gives mirror-image forms that rotate plane-polarised light in opposite directions.
立体异构包括烯烃中的E/Z（顺反）异构，以及光学异构——不对称碳原子产生的镜像体，使平面偏振光向相反方向旋转。
3. Reaction Mechanisms and Curly Arrows | 反应机理与弯箭头
A reaction mechanism shows the step-by-step movement of electrons during a reaction. Curly arrows indicate electron pair movement: a full arrow shows the movement of a lone pair or bond pair, while a half-headed arrow shows the movement of a single electron.
反应机理展示反应过程中电子的逐步转移。弯箭头表示电子对的移动：全箭头表示孤对电子或成键电子的移动，半箭头表示单电子的移动。
Two key mechanisms in IB are nucleophilic substitution (SN1 and SN2) and electrophilic addition. In SN2, the nucleophile attacks in one step with inversion of configuration; in SN1, a carbocation intermediate is formed first.
IB中两个关键机理是亲核取代（SN1和SN2）和亲电加成。在SN2中，亲核试剂一步进攻并伴随构型翻转；在SN1中，首先形成碳正离子中间体。
4. Substitution Reactions | 取代反应
A substitution reaction replaces one atom or group with another. Two important types are nucleophilic substitution and electrophilic substitution.
取代反应是用另一个原子或基团替换原有的一个原子或基团。两种重要类型是亲核取代和亲电取代。
Halogenoalkanes undergo nucleophilic substitution with aqueous NaOH to form alcohols, with ammonia to form amines, and with cyanide ions to form nitriles, which can be hydrolysed to carboxylic acids.
卤代烷烃与NaOH水溶液发生亲核取代生成醇，与氨反应生成胺，与氰根离子反应生成腈，腈再水解得到羧酸。
Benzene undergoes electrophilic substitution, e.g. nitration with HNO₃/H₂SO₄ and halogenation with a halogen carrier. The delocalised π system stabilises the intermediate and retains the aromatic ring after loss of a proton.
苯发生亲电取代反应，例如用HNO₃/H₂SO₄进行硝化，或在载体存在下卤化。离域π体系稳定中间体，并在失去质子后恢复芳环结构。
5. Addition Reactions | 加成反应
Addition reactions occur when two reactants combine to form a single product with no other products. They are typical of unsaturated compounds such as alkenes.
加成反应是指两种反应物结合生成单一产物且没有其他副产物的反应。烯烃等不饱和化合物通常发生此类反应。
Electrophilic addition of HX to an alkene follows Markovnikov’s rule: the hydrogen attaches to the carbon with the most hydrogen atoms, forming the more stable carbocation. For example, propene with HBr gives 2-bromopropane as the major product.
烯烃与HX的亲电加成遵循马尔科夫尼科夫规则：氢原子加到含氢较多的碳上，形成更稳定的碳正离子。例如，丙烯与HBr反应主要生成2-溴丙烷。
Alkenes also undergo catalytic hydrogenation (H₂/Pt), halogenation (Br₂), and hydrolysis to form alcohols. Bromine water is a standard test for unsaturation; the orange colour disappears.
烯烃还能发生催化加氢（H₂/Pt）、卤化（Br₂）和水合生成醇。溴水是检验不饱和键的常用试剂；橙色会褪去。
6. Elimination Reactions | 消除反应
An elimination reaction removes a small molecule (e.g. H₂O or HX) from a saturated compound to form an unsaturated compound, usually an alkene.
消除反应是从饱和化合物中脱去一个小分子（如水或卤化氢），形成不饱和化合物，通常是烯烃。
Halogenoalkanes undergo elimination with ethanolic KOH (or NaOH) when heated, producing an alkene. For example, 2-bromopropane with ethanolic KOH gives propene.
卤代烷烃在加热条件下与醇制KOH（或NaOH）溶液反应发生消除，生成烯烃。例如，2-溴丙烷与乙醇钾溶液反应生成丙烯。
Elimination and substitution compete; the choice of solvent is critical. Aqueous conditions favour substitution, whereas ethanolic (alcoholic) conditions favour elimination.
消除与取代是竞争反应；溶剂的选择至关重要。水溶液条件利于取代，醇溶液条件利于消除。
7. Oxidation and Reduction | 氧化与还原
In organic chemistry, oxidation often means adding oxygen or removing hydrogen, while reduction means adding hydrogen or removing oxygen. Redox can also be viewed in terms of electrons.
在有机化学中，氧化通常指增加氧或减少氢，还原指增加氢或减少氧。氧化还原也可以从电子的角度理解。
Primary alcohols are oxidised to aldehydes and then to carboxylic acids by acidified K₂Cr₂O₇ (orange to green). Secondary alcohols are oxidised to ketones; tertiary alcohols are not oxidised under these conditions.
伯醇被酸性K₂Cr₂O₇氧化成醛，再进一步氧化成羧酸（橙色变绿色）。仲醇被氧化成酮；叔醇在这种条件下不被氧化。
Aldehydes are easily oxidised to carboxylic acids, and they reduce Tollens’ reagent (silver mirror) and Fehling’s solution (brick-red precipitate). Ketones do not react in these tests.
醛很容易被氧化成羧酸，并能还原托伦斯试剂（银镜）和斐林试剂（砖红色沉淀）。酮在这些测试中不反应。
Carboxylic acids can be reduced to primary alcohols using strong reducing agents such as lithium aluminium hydride (LiAlH₄).
羧酸可用强还原剂如氢化铝锂（LiAlH₄）还原成伯醇。
8. Acidity and Basicity | 酸性与碱性
Organic acids release H⁺ from an O–H or C–H bond. Their strength depends on the stability of the conjugate base formed after deprotonation.
有机酸从O–H或C–H键中释放H⁺。其强度取决于去质子后生成的共轭碱的稳定性。
Carboxylic acids are weak acids (pKa ≈ 4–5) because the carboxylate anion is stabilised by resonance and the inductive effect of the carbonyl oxygen. Phenol is weakly acidic (pKa ≈ 10) due to delocalisation of the phenoxide negative charge. Alcohols are almost neutral (pKa ≈ 16–18).
羧酸是弱酸（pKa约4–5），因为羧酸根负离子通过共振和羰基氧的诱导效应而稳定。苯酚具有弱酸性（pKa约10），因为苯氧负离子的负电荷可以离域。醇几乎呈中性（pKa约16–18）。
Amines are weak bases. The lone pair on nitrogen accepts a proton. Aliphatic amines are stronger bases than aromatic amines because in aromatic amines the lone pair is partly delocalised into the ring.
胺是弱碱。氮原子上的孤对电子可以接受质子。脂肪胺的碱性比芳香胺强，因为芳香胺中孤对电子部分离域到环上。
9. Polymerisation | 聚合反应
Polymers are large molecules made from repeating monomer units. Two main types are addition polymers and condensation polymers.
聚合物是由重复的单体单元组成的大分子。主要分为加成聚合物和缩合聚合物两类。
Addition polymerisation requires unsaturated monomers, e.g. ethene forms poly(ethene). The reaction involves opening the C=C double bond and linking monomers without loss of any small molecule.
加成聚合需要不饱和单体，例如乙烯生成聚乙烯。该反应打开C=C双键并将单体连接起来，没有小分子副产物损失。
Condensation polymerisation occurs between monomers with two functional groups, releasing a small molecule such as water. Polyesters form from a dicarboxylic acid and a diol; polyamides form from a dicarboxylic acid and a diamine (e.g. nylon-66).
缩合聚合发生在具有两个官能团的单体之间，释放水等小分子。聚酯由二元羧酸和二元醇形成；聚酰胺由二元羧酸和二元胺形成（如尼龙-66）。
10. Spectroscopy and Structure Elucidation | 光谱与结构鉴定
Spectroscopic techniques help determine the structure of organic compounds. IB Chemistry requires interpretation of mass spectra, IR spectra, and ¹H NMR spectra.
光谱技术有助于确定有机化合物的结构。IB化学要求解析质谱、红外光谱和¹H核磁共振谱。
Mass spectrometry gives the molecular mass (M⁺) and fragmentation patterns. The molecular ion peak with the highest m/z gives the relative molecular mass, and isotope peaks (e.g. M+2 for chlorine/bromine) provide structural clues.
质谱提供分子质量（M⁺）和碎片模式。质荷比最高的分子离子峰给出相对分子质量，同位素峰（如氯/溴的M+2峰）提供结构线索。
Infrared spectroscopy identifies functional groups through characteristic absorption bands: O–H around 3200–3600 cm⁻¹, C=O around 1680–1750 cm⁻¹, and N–H around 3300 cm⁻¹.
红外光谱通过特征吸收峰识别官能团：O–H在3200–3600 cm⁻¹，C=O在1680–1750 cm⁻¹，N–H在3300 cm⁻¹附近。
¹H NMR shows the number of hydrogen environments (number of peaks or signals), the integration (relative area), and chemical shifts. Spin-spin splitting (e.g. triplet from neighbouring CH₂) indicates adjacent hydrogen count.
¹H核磁共振谱显示氢环境的种类（峰数）、积分面积（相对氢数）和化学位移。自旋-自旋裂分（如相邻CH₂产生的三重峰）可推断相邻氢的数目。
11. Organic Synthesis Strategies | 有机合成策略
Synthetic design involves converting a starting material into a target molecule through a sequence of reactions. IB students should be able to devise routes using their knowledge of functional group transformations.
合成设计是指通过一系列反应将原料分子转化为目标分子。IB学生应能运用官能团转化知识设计合成路线。
Key interconversions include: alcohol ↔ halogenoalkane, alcohol → aldehyde/ketone → carboxylic acid, halogenoalkane → amine via NH₃, and alkene → alcohol via hydration. Reaction conditions and reagents must be chosen carefully, e.g. acidified K₂Cr₂O₇ for oxidation, LiAlH₄ for reduction.
关键的转化包括：醇↔卤代烷烃，醇→醛/酮→羧酸，卤代烷烃经NH₃转化为胺，烯烃经水合生成醇。必须小心选择试剂和条件，例如氧化用酸性K₂Cr₂O₇，还原用LiAlH₄。
Retrosynthetic thinking begins with the target molecule and works backwards to simpler precursors. This helps identify possible starting materials and bond disconnections.
逆合成分析从目标分子出发，反向推导到更简单的前体。这有助于确定可能的原料和断键位置。
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