Functional Group Chemistry | 官能团的化学性质

📚 Functional Group Chemistry | 官能团的化学性质

In IB Chemistry, organic chemistry is organised around functional groups — specific atoms or bonds within a molecule that determine its characteristic reactions. Understanding the chemical properties of these groups is essential for predicting reactivity, designing synthetic routes, and interpreting spectroscopic data.

在IB化学中，有机化学围绕官能团展开——官能团是分子内决定其特征反应的特定原子或化学键。理解这些基团的化学性质，对于预测反应活性、设计合成路线以及解读波谱数据都至关重要。

1. Overview of Functional Groups | 官能团概述

A functional group is an atom or group of atoms that gives an organic molecule its distinctive chemical behaviour. The same functional group undergoes similar reactions regardless of the rest of the molecule, although neighbouring groups can influence reactivity through steric and electronic effects.

官能团是赋予有机分子独特化学行为的原子或原子团。无论分子其余部分如何，同一官能团都会发生相似的反应，尽管相邻基团可能通过空间位阻和电子效应影响反应活性。

Common functional groups include alcohols (—OH), haloalkanes (—X), aldehydes (—CHO), ketones (—C(=O)—), carboxylic acids (—COOH), esters (—COOR), amines (—NH₂) and amides (—CONH₂).

常见官能团包括醇(—OH)、卤代烷(—X)、醛(—CHO)、酮(—C(=O)—)、羧酸(—COOH)、酯(—COOR)、胺(—NH₂)和酰胺(—CONH₂)。
Reactions generally occur at the functional group, while the hydrocarbon skeleton remains unchanged.

反应通常发生在官能团位置，而碳氢骨架保持不变。
In IB examinations, you must be able to identify functional groups from structural formulas and predict reaction products.

在IB考试中，你必须能够从结构式识别官能团并预测反应产物。

2. Alcohols: Oxidation | 醇：氧化反应

Primary alcohols can be oxidised to aldehydes and then to carboxylic acids, while secondary alcohols are oxidised to ketones. Tertiary alcohols do not undergo oxidation under ordinary conditions because the carbon bearing the —OH group has no hydrogen atom attached.

伯醇可以被氧化为醛，再进一步氧化为羧酸；仲醇被氧化为酮。叔醇在通常条件下不发生氧化反应，因为连接—OH基团的碳原子上没有氢原子。

RCH₂OH → RCHO → RCOOH

Acidified K₂Cr₂O₇ or KMnO₄ is commonly used as the oxidising agent. The colour change of K₂Cr₂O₇ from orange to green indicates a successful oxidation.

常用的氧化剂是酸化的K₂Cr₂O₇或KMnO₄。K₂Cr₂O₇由橙色变为绿色，表明氧化反应成功发生。
Distillation of the aldehyde product before further oxidation allows isolation of the aldehyde.

在醛进一步氧化之前通过蒸馏将其分离，可得到醛产物。
Secondary alcohols require milder conditions and produce ketones, which are resistant to further oxidation.

仲醇在较温和条件下生成酮，而酮对进一步氧化具有抵抗力。

3. Alcohols: Dehydration and Substitution | 醇：脱水与取代

Alcohols undergo elimination of water (dehydration) to form alkenes when heated with concentrated H₂SO₄ or H₃PO₄. Alternatively, the —OH group can be replaced by a halogen atom in a nucleophilic substitution reaction.

醇在浓H₂SO₄或H₃PO₄加热条件下发生脱水反应（消除反应）生成烯烃。另外，—OH基团也可以通过亲核取代反应被卤素原子替换。

CH₃CH₂OH → CH₂=CH₂ + H₂O

Dehydration follows Zaitsev’s rule: the more substituted alkene is preferred when more than one product is possible.

脱水反应遵循扎伊采夫规则：当可能生成多种产物时，更稳定的取代烯烃优先形成。
Reaction with hydrogen halides, e.g. HCl or HBr, converts alcohols to haloalkanes. The reactivity order is tertiary > secondary > primary.

与卤化氢（如HCl或HBr）反应可将醇转化为卤代烷。反应活性顺序为叔醇 > 仲醇 > 伯醇。
PCl₃, PCl₅ or SOCl₂ also convert alcohols to chloroalkanes with better yields.

PCl₃、PCl₅或SOCl₂也能将醇转化为氯代烷，且产率更高。

4. Haloalkanes: Nucleophilic Substitution | 卤代烷：亲核取代

Haloalkanes contain a polar C—X bond, making the carbon atom electron-deficient and susceptible to attack by nucleophiles. The halogen atom is replaced by the nucleophile in an Sₙ1 or Sₙ2 mechanism.

卤代烷含有极性的C—X键，使碳原子缺电子，容易受到亲核试剂的进攻。卤素原子在Sₙ1或Sₙ2机制中被亲核试剂取代。

Sₙ2 reactions are one-step bimolecular processes with inversion of configuration at the chiral carbon. They are favoured by primary haloalkanes and strong nucleophiles.

Sₙ2反应是一步双分子过程，手性碳构型发生翻转。伯卤代烷和强亲核试剂有利于Sₙ2反应。
Sₙ1 reactions proceed through a carbocation intermediate, giving racemic products from chiral haloalkanes. Tertiary haloalkanes favour Sₙ1 because of stable tertiary carbocations.

Sₙ1反应通过碳正离子中间体进行，手性卤代烷生成外消旋产物。叔卤代烷由于能形成稳定的叔碳正离子而倾向于Sₙ1反应。
Common nucleophiles include OH⁻ (forming alcohols), CN⁻ (forming nitriles) and NH₃ (forming amines).

常见亲核试剂包括OH⁻（生成醇）、CN⁻（生成腈）和NH₃（生成胺）。

5. Haloalkanes: Elimination | 卤代烷：消除反应

When haloalkanes are heated with a strong base such as alcoholic KOH or NaOH, they undergo elimination to form alkenes. The base removes a β-hydrogen atom while the halogen leaves simultaneously.

卤代烷与强碱（如醇溶液中的KOH或NaOH）加热时发生消除反应生成烯烃。碱同时夺取β-氢原子，卤素以离去基团形式离开。

CH₃CH₂Br + KOH → CH₂=CH₂ + KBr + H₂O

Elimination competes with substitution; alcoholic conditions favour elimination, while aqueous conditions favour substitution.

消除与取代相互竞争；醇溶液条件有利于消除，水溶液条件有利于取代。
The product distribution depends on the structure of the haloalkane, the base strength and temperature.

产物分布取决于卤代烷的结构、碱的强度和温度。
Zaitsev’s rule applies: the more substituted alkene is the major product.

扎伊采夫规则同样适用：取代程度更高的烯烃是主要产物。

6. Aldehydes and Ketones: Nucleophilic Addition | 醛和酮：亲核加成

The carbonyl group C=O is polarised with a partial positive charge on carbon. Aldehydes and ketones undergo nucleophilic addition reactions, where a nucleophile adds across the C=O double bond.

羰基C=O发生极化，碳原子带有部分正电荷。醛和酮发生亲核加成反应，亲核试剂加成到C=O双键上。

Reduction with NaBH₄ converts aldehydes to primary alcohols and ketones to secondary alcohols.

用NaBH₄还原可将醛转化为伯醇，将酮转化为仲醇。
Hydrogen cyanide (HCN) adds to form cyanohydrins, which are valuable in extending carbon chains.

氰化氢(HCN)加成生成氰醇，可用于延长碳链。
2,4-dinitrophenylhydrazine (Brady’s reagent) reacts with all aldehydes and ketones to give yellow-orange precipitates, providing a simple qualitative test.

2,4-二硝基苯肼（布雷迪试剂）与所有醛和酮反应生成黄橙色沉淀，可用于定性检验。

7. Aldehydes vs Ketones: Oxidation and Fehling’s Test | 醛与酮：氧化反应与斐林检验

Aldehydes are easily oxidised to carboxylic acids, whereas ketones resist oxidation under mild conditions. This difference forms the basis of distinguishing tests using Tollens’ reagent or Fehling’s solution.

醛容易被氧化为羧酸，而酮在温和条件下不易被氧化。这一差异构成了用多伦试剂或斐林溶液进行鉴别的基础。

Test	Aldehyde	Ketone
Tollens’ reagent (ammoniacal AgNO₃)	Silver mirror	No reaction
Fehling’s solution (Cu²⁺ in alkaline tartrate)	Brick-red Cu₂O precipitate	No reaction

Tollens’ reagent oxidises aldehydes to carboxylate ions while Ag⁺ is reduced to metallic silver.

多伦试剂将醛氧化为羧酸根离子，同时Ag⁺被还原为金属银。
Fehling’s solution is reduced from deep blue Cu²⁺ to brick-red Cu₂O.

斐林溶液从深蓝色的Cu²⁺被还原为砖红色的Cu₂O。
Ketones do not react because they lack a hydrogen atom attached to the carbonyl carbon.

酮不发生反应，因为羰基碳上没有连接氢原子。

8. Carboxylic Acids: Acidity and Esterification | 羧酸：酸性与酯化

Carboxylic acids are weak acids that partially dissociate in water. The carboxyl group —COOH releases a proton to form a carboxylate ion. The negative charge is stabilised by resonance, making carboxylic acids more acidic than alcohols or phenols.

羧酸是弱酸，在水中部分电离。羧基—COOH释放质子后形成羧酸根离子，负电荷通过共振离域而稳定，因此羧酸的酸性强于醇或酚。

RCOOH ⇌ RCOO⁻ + H⁺

Carboxylic acids react with bases and carbonates to form salts, and with metals to release hydrogen gas.

羧酸与碱和碳酸盐反应生成盐，与活泼金属反应释放氢气。
Esterification with an alcohol in the presence of concentrated H₂SO₄ produces an ester and water. This is a reversible equilibrium reaction.

在浓H₂SO₄催化下与醇发生酯化反应生成酯和水，该反应是可逆平衡反应。
The ester formed from ethanol and ethanoic acid is ethyl ethanoate, which has a characteristic fruity smell.

乙醇与乙酸反应生成的酯是乙酸乙酯，具有特征性水果香味。

9. Esters: Hydrolysis and Saponification | 酯：水解与皂化

Esters can be hydrolysed back to carboxylic acids and alcohols. Hydrolysis in acidic conditions is reversible, whereas alkaline hydrolysis (saponification) is irreversible and produces carboxylate salts.

酯可以水解回到羧酸和醇。酸性条件下的水解是可逆的，而碱性水解（皂化）不可逆，生成羧酸盐。

RCOOR’ + NaOH → RCOONa + R’OH

Acid-catalysed hydrolysis uses dilute H₂SO₄ or HCl and yields carboxylic acid and alcohol.

酸催化水解使用稀H₂SO₄或HCl，产物为羧酸和醇。
Saponification is used in soap manufacture: triglycerides (esters of glycerol) are hydrolysed with NaOH to form soap.

皂化用于制皂：甘油三酯（甘油的酯）与NaOH水解生成肥皂。
Ester hydrolysis is the reverse of esterification, so the same equilibrium constant applies in acidic conditions.

酯的水解是酯化的逆反应，因此在酸性条件下适用相同的平衡常数。

10. Amines: Basicity and Acylation | 胺：碱性与酰化

Amines are organic bases because the nitrogen atom has a lone pair of electrons that can accept a proton. Aliphatic amines are stronger bases than ammonia, while aromatic amines such as phenylamine are weaker due to delocalisation of the lone pair into the benzene ring.

胺是有机碱，因为氮原子有孤对电子可以接受质子。脂肪胺的碱性强于氨，而芳香胺（如苯胺）因孤对电子离域到苯环中而碱性较弱。

Amines react with acids to form ammonium salts, e.g. CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻.

胺与酸反应生成铵盐，例如CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻。
Primary amines react with acyl chlorides or acid anhydrides to form substituted amides in an acylation reaction.

伯胺与酰氯或酸酐发生酰化反应，生成取代酰胺。
This acylation is an important step in the synthesis of paracetamol (acetaminophen) from 4-aminophenol.

该酰化反应是对氨基苯酚合成扑热息痛（对乙酰氨基酚）的重要步骤。

11. Amides: Hydrolysis | 酰胺：水解

Amides are derived from carboxylic acids and ammonia or amines. They are neutral compounds with high boiling points due to hydrogen bonding. Unlike amines, amides do not show significant basicity because the nitrogen lone pair is delocalised with the carbonyl group.

酰胺由羧酸与氨或胺衍生而来。它们呈中性，由于氢键而具有较高沸点。与胺不同，酰胺不表现出明显碱性，因为氮的孤对电子与羰基共轭离域。

RCONH₂ + H₂O → RCOOH + NH₃

Acid-catalysed hydrolysis of amides produces carboxylic acids and ammonium salts.

酰胺的酸催化水解生成羧酸和铵盐。
Base-catalysed hydrolysis produces carboxylate salts and ammonia or amines.

碱催化水解生成羧酸盐和氨或胺。
Peptide bonds in proteins are amide linkages; their hydrolysis by enzymes is fundamental to protein digestion.

蛋白质中的肽键属于酰胺键；酶催化的水解是蛋白质消化的基础。

12. Phenols: Weak Acidity and Coupling Reactions | 酚：弱酸性与偶联反应

Phenols contain an —OH group attached directly to a benzene ring. They are weakly acidic, stronger than alcohols but weaker than carboxylic acids. The phenoxide ion is stabilised by resonance, explaining the enhanced acidity.

酚含有直接连接在苯环上的—OH基团，呈弱酸性，强于醇但弱于羧酸。苯氧负离子通过共振稳定，这解释了酚的酸性增强的原因。

C₆H₅OH ⇌ C₆H₅O⁻ + H⁺ (pKₐ ≈ 10)

Phenols do not react with carbonates or hydrogencarbonates, distinguishing them from carboxylic acids.

酚不与碳酸盐或碳酸氢盐反应，这可用于区分羧酸和酚。
Phenols undergo electrophilic aromatic substitution more readily than benzene. Bromine water decolorises, forming a white precipitate of 2,4,6-tribromophenol.

酚比苯更容易发生亲电芳香取代。溴水褪色并生成2,4,6-三溴苯酚白色沉淀。
Phenols couple with diazonium salts to form brightly coloured azo dyes.

酚与重氮盐偶联生成颜色鲜艳的偶氮染料。

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Functional Group Chemistry | 官能团的化学性质