HKDSE Chemistry Core
Section 11: Chemistry of Carbon Compounds | 碳化合物的化學

🌡️ Melting/Boiling Points & Density | 熔點/沸點與密度

• 1. Hydrogen Bonding (氫鍵): Alcohols, carboxylic acids, and amides have much higher m.p. and b.p. than alkanes/alkenes of similar mass due to the presence of strong intermolecular hydrogen bonds. 醇、羧酸和酰胺由於存在強大的分子間氫鍵，其熔點和沸點遠高於質量相若的烷烴/烯烴。
• 2. Polar Molecules (極性分子): Compounds with polar functional groups (e.g., aldehydes, ketones, haloalkanes) experience dipole-dipole interactions, giving them higher m.p./b.p. than non-polar hydrocarbons of similar size, but lower than those with hydrogen bonds. 帶有極性官能基的化合物（如醛、酮、鹵代烷）具有偶極-偶極引力，其熔點/沸點高於體積相若的非極性烴類，但低於具有氫鍵的分子。
• 3. Molecular Size (分子體積): For molecules in the same homologous series, as the carbon chain gets longer, the molecular size increases, leading to stronger van der Waals’ forces (dispersion forces) between molecules. Thus, m.p., b.p., and density increase. 對於同一同系物，碳鏈越長，分子體積越大，分子間的范德華力（色散力）越強。因此熔點、沸點和密度上升。
• 4. Shape (分子形狀): For isomers, a straight chain provides a larger surface area for intermolecular contact, strengthening van der Waals’ forces and favoring a higher boiling point (b.p.). On the other hand, a highly branched chain makes the molecule more spherical and symmetrical, allowing it to pack more closely in a solid crystal lattice, which favors a higher melting point (m.p.) and density. 對於異構體，直鏈提供較大的分子間接觸表面積，增強范德華力，有利於較高的沸點（b.p.）。另一方面，高度支鏈使分子更接近球體且對稱，使其在固體晶格中能更緊密地堆積，從而有利於較高的熔點（m.p.）和密度。

💧 Solubility in Water | 水溶性

“Like dissolves like” (相似相溶):

• Hydrocarbons (Alkanes, Alkenes) and Haloalkanes are insoluble in water (hydrophobic). 烴類和鹵代烷不溶於水（疏水性）。
• Lower alcohols, aldehydes, ketones, and carboxylic acids (1-3 carbons) are soluble in water because their hydrophilic functional groups can form hydrogen bonds with water. 低級醇、醛、酮和羧酸可溶於水，因為其親水官能基能與水形成氫鍵。
• As the carbon chain lengthens, the hydrophobic effect dominates, and solubility in water decreases. 隨著碳鏈變長，疏水效應佔優，水溶性下降。

⚠️ Exam Trap: Markovnikov’s Rule | 考試陷阱：馬可尼科夫法則

When adding \( \text{HX} \) or \( \text{H}_2\text{O} \) to an unsymmetrical alkene, the Hydrogen atom attaches to the carbon of the double bond that already has more hydrogen atoms. This forms the more stable carbocation intermediate, leading to the major product. 當 \( \text{HX} \) 加成到不對稱烯烴時，氫原子會連接到原本已帶有較多氫原子的雙鍵碳上。這會形成較穩定的碳陽離子中間體，從而產生主產物。

🧼 1. Soap and Detergents | 肥皂與清潔劑

• Saponification (皂化反應): Fat/Oil + \( \text{NaOH(aq)} \xrightarrow{\text{heat}} \) Soap (Sodium salt of fatty acid) + Glycerol (丙三醇).
• Cleaning Action: Soap has a hydrophilic ionic head (dissolves in water) and a hydrophobic hydrocarbon tail (dissolves in oil/grease). It acts as an emulsifier, breaking oil into tiny droplets (micelles) suspended in water. 肥皂具有親水性離子頭（溶於水）和疏水性碳氫尾（溶於油污）。它作為乳化劑，將油污分解成懸浮在水中的微小液滴。

💊 2. Aspirin | 阿士匹靈

• Aspirin is an analgesic (painkiller). It is synthesized via Esterification (酯化反應).
• Reactants: Salicylic acid (水楊酸) + Ethanoic anhydride (乙酸酐) or Ethanoyl chloride.
• Note: Ethanoic acid can be used with conc. \( \text{H}_2\text{SO}_4 \), but ethanoic anhydride is preferred as it gives a higher yield and doesn’t produce water (which could reverse the reaction). 乙酸酐是更佳選擇，因為產率較高且不產生水。

🔗 3. Polymers | 聚合物