📚 Organic Chemistry | 有机化学
Organic chemistry is the study of carbon-based compounds and their reactions. In the IB Chemistry course, it spans from identifying functional groups to understanding reaction mechanisms and spectroscopic analysis. Mastering organic chemistry is essential for success in both Standard Level and Higher Level assessments.
有机化学是研究碳基化合物及其反应的学科。在IB化学课程中，它涵盖从识别官能团到理解反应机理和光谱分析等广泛内容。掌握有机化学对于在标准级别和高级别评估中取得优异成绩至关重要。
1. Fundamentals: Functional Groups, Nomenclature and Isomerism | 有机化学基础：官能团、命名与异构
Organic compounds are grouped into homologous series, each member differing by a –CH₂– unit. The functional group determines the chemical reactivity of the molecule. A table of common series is shown below.
有机化合物按照同系物分组，每个成员相差一个–CH₂–单元。官能团决定了分子的化学反应性。下表列出了一系列常见的同系物。
| 系列 (Homologous Series) | 官能团 (Functional Group) | 通式 (General Formula) |
|---|---|---|
| Alkane | C–C, C–H single bonds | CₙH₂ₙ₊₂ |
| Alkene | C=C double bond | CₙH₂ₙ |
| Alkyne | C≡C triple bond | CₙH₂ₙ₋₂ |
| Alcohol | –OH (hydroxyl) | CₙH₂ₙ₊₁OH |
| Aldehyde | –CHO | CₙH₂ₙO |
| Ketone | >C=O | CₙH₂ₙO |
| Carboxylic acid | –COOH | CₙH₂ₙO₂ |
| Ester | –COO– | CₙH₂ₙO₂ |
| Amine | –NH₂ | CₙH₂ₙ₊₃N |
| Halogenoalkane | –X (F, Cl, Br, I) | CₙH₂ₙ₊₁X |
IUPAC nomenclature follows a systematic set of rules: identify the longest continuous carbon chain, number the chain so that the functional group or multiple bond receives the lowest possible locant, and list substituents alphabetically with their position numbers. For example, the molecule with a five-carbon chain and a methyl group on the second carbon is named 2-methylpentane.
IUPAC命名遵循一套系统规则：确定最长的连续碳链，对链进行编号，使官能团或多重键得到尽可能小的位次，并按字母顺序列出取代基及其位置编号。例如，含五个碳原子的链且在第二个碳上有一个甲基的分子被命名为2-甲基戊烷。
requires two different groups on each carbon of a C=C bond, and optical isomerism occurs in molecules containing a chiral centre, giving non-superimposable mirror images.
当化合物具有相同的分子式但排列不同时，就产生异构现象。构造异构包括碳链异构、位置异构和官能团异构。立体异构则连接顺序相同，但空间排列不同：几何（顺/反）异构要求双键每个碳上连有两个不同的基团，而光学异构发生在含有手性中心的分子中，呈现出不可重合的镜像。
2. Alkanes: Combustion and Free-Radical Substitution | 烷烃：燃烧与自由基取代
Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂. They are relatively unreactive due to strong C–C and C–H bonds, but they undergo complete combustion in excess oxygen to produce carbon dioxide and water, and incomplete combustion to give carbon monoxide or soot.
烷烃是饱和烃，通式为CₙH₂ₙ₊₂。由于牢固的C–C和C–H键，它们相对不活泼，但在过量氧气中能发生完全燃烧生成二氧化碳和水，不完全燃烧则生成一氧化碳或碳粒。
The key reaction of alkanes is free-radical substitution with halogens in the presence of UV light. The mechanism involves three stages: initiation, where halogen molecules split into radicals; propagation, where a radical abstracts a hydrogen to form hydrogen halide and another radical; and termination, where two radicals combine.
烷烃的关键反应是在紫外光下与卤素的自由基取代。该机理包括三个阶段：引发阶段卤素分子分裂成自由基；链增长阶段，一个自由基夺取氢原子生成卤化氢并产生另一个自由基；链终止阶段，两个自由基结合。
Cl₂ → 2 Cl•
CH₄ + Cl• → •CH₃ + HCl
•CH₃ + Cl₂ → CH₃Cl + Cl•
2 Cl• → Cl₂, etc.
Further substitution can lead to a mixture of chlorinated products. The reaction is used to introduce halogen atoms into an alkane skeleton for further functionalisation.
进一步取代会导致氯化产物的混合物。该反应用于向烷烃骨架引入卤素原子，以实现进一步转化。
3. Alkenes: Electrophilic Addition | 烯烃：亲电加成
are much more reactive than alkanes. The typical reaction is electrophilic addition, where the electron-rich π bond attracts an electrophile. Addition of bromine water (orange to colourless) serves as a test for unsaturation.
烯烃含有C=C双键，比烷烃活泼得多。其典型反应为亲电加成，富电子的π键吸引亲电试剂。加入溴水（橙色变为无色）可用作不饱和性的检验。
Addition of hydrogen halides follows Markovnikov's rule: the hydrogen atom adds to the carbon with more hydrogen atoms already attached. For example, propene with HBr gives mainly 2-bromopropane. The mechanism proceeds via formation of the more stable carbocation intermediate.
卤化氢的加成遵循马氏规则：氢原子加在原来连有较多氢原子的碳上。例如，丙烯与HBr主要生成2-溴丙烷。机理通过形成更稳定的碳正离子中间体进行。
CH₃CH=CH₂ + HBr → CH₃CHBrCH₃ (major product)
Hydration of alkenes with steam and phosphoric acid catalyst produces alcohols. Overall, alkenes are essential intermediates in synthesis and polymerisation.
在磷酸催化下，烯烃与水蒸气发生水合反应生成醇。总之，烯烃在合成与聚合中都是极其重要的中间体。
4. Halogenoalkanes: Nucleophilic Substitution | 卤代烷：亲核取代
Halogenoalkanes contain a polar C–X bond, making the carbon atom susceptible to attack by nucleophiles. Nucleophilic substitution can proceed via two distinct mechanisms: SN1 and SN2. The SN2 mechanism is a concerted, single-step process with backside attack and inversion of configuration, favoured by primary halogenoalkanes.
卤代烷含有极性的C–X键，使碳原子易受亲核试剂进攻。亲核取代可通过两种不同机理进行：SN1和SN2。SN2是协同的一步过程，背面进攻并伴随构型翻转，倾向发生在伯卤代烷中。
The SN1 mechanism operates in two steps: slow ionisation to form a planar carbocation, followed by rapid nucleophilic attack, leading to racemisation if the carbon is chiral. Tertiary halogenoalkanes favour SN1 because of carbocation stability.
SN1机理分两步进行：缓慢电离生成平面碳正离子，随后快速的亲核进攻；若碳为手性，则导致外消旋化。叔卤代烷因碳正离子稳定性而倾向SN1。
Typical nucleophiles include hydroxide ions (forming alcohols), ammonia (forming amines) and cyanide ions (extending the carbon chain). Halogenoalkanes also undergo elimination to form alkenes when heated with ethanolic NaOH, with the major product predicted by Zaitsev's rule.
常见的亲核试剂包括氢氧根离子（生成醇）、氨（生成胺）和氰根离子（延长碳链）。卤代烷与氢氧化钠的乙醇溶液加热时还可发生消除反应生成烯烃，主产物可由扎依采夫规则预测。
5. Alcohols: Oxidation and Elimination | 醇：氧化与消除
Alcohols are classified as primary, secondary or tertiary according to the number of alkyl groups attached to the carbon bearing the –OH group. Their most important reaction is oxidation: primary alcohols can be oxidised to aldehydes (distillation) and then to carboxylic acids (reflux), while secondary alcohols yield ketones. Tertiary alcohols resist oxidation under normal conditions.
醇按与–OH所在碳相连的烷基数目分为伯、仲、叔醇。它们最重要的反应是氧化：伯醇可被氧化成醛（蒸馏）再氧化成羧酸（回流），仲醇生成酮；叔醇在常规条件下难以被氧化。
CH₃CH₂OH + [O] → CH₃CHO + H₂O
CH₃CHO + [O] → CH₃COOH
Common oxidising agents are acidified potassium dichromate(VI) or potassium manganate(VII). Alcohols also undergo dehydration to alkenes when heated with concentrated sulfuric acid or over an aluminium oxide catalyst.
常用氧化剂为酸化重铬酸钾(VI)或高锰酸钾(VII)。醇在浓硫酸加热或在氧化铝催化下还可发生脱水反应生成烯烃。
6. Carbonyl Compounds: Aldehydes and Ketones | 羰基化合物：醛和酮
ve at least one hydrogen atom attached to the carbonyl carbon, which enables them to be oxidised to carboxylic acids. Ketones lack this hydrogen and are therefore resistant to mild oxidation.
醛和酮都含有羰基C=O。醛在羰基碳上至少连有一个氢原子，这使得它们能氧化成羧酸。酮没有这个氢，因此对温和氧化有抵抗力。
Because of this difference, aldehydes reduce Tollens' reagent (silver mirror) and Fehling's solution (red precipitate), while ketones give no reaction. Both carbonyl compounds undergo nucleophilic addition; for instance, with hydrogen cyanide to form hydroxynitriles, a useful reaction for chain extension.
由于这种区别，醛能还原托伦试剂（银镜反应）和斐林溶液（红色沉淀），而酮则无反应。两类羰基化合物均可发生亲核加成；例如，与氰化氢反应生成羟腈，这是增长碳链的有用反应。
Reduction with NaBH₄ or LiAlH₄ converts aldehydes to primary alcohols and ketones to secondary alcohols. Methyl ketones and acetaldehyde also give the iodoform reaction, a pale yellow precipitate of CHI₃ with iodine and alkali.
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