Chapter 2: Carbon Compound

2.1 Types of Carbon Compounds

• Organic compounds: from living things; carbon bonded covalently to H, N, S, P etc. Inorganic carbon compounds: oxides of carbon, carbonates, cyanides. (p.64)
• Hydrocarbons contain only carbon and hydrogen; saturated hydrocarbons have only single bonds, unsaturated have at least one double or triple bond. Non hydrocarbons contain other elements (O, N, P, halogens). (p.65)
• Petroleum is a mixture of hydrocarbons refined by fractional distillation and cracking. (p.66)
• In fractional distillation, lower boiling point fractions rise to the top; higher boiling point fractions collect at the bottom. Boiling point rises with molecule size due to stronger van der Waals forces. (p.66)
• Fractions: petroleum gas (C₁–C₄, cooking gas); petrol; naphtha (petrochemical raw material); kerosene (aircraft); diesel (buses, lorries); lubricating oil; fuel oil (ships, power stations); bitumen (roads). (p.67)
• Small molecules: low boiling point, bright colour, highly combustible, less viscous. Big molecules: high boiling point, dark colour, low combustibility, more viscous. (p.67)
• Cracking breaks long chain hydrocarbons into smaller ones at high temperature and pressure using Al₂O₃/SiO₂ catalyst; products include petrol and short alkanes/alkenes for polymers, detergents etc. (p.68)
• Example: C₁₀H₂₂ → 2C₅H₁₀ + H₂; C₇H₁₆ → C₂H₄ + C₅H₁₂. (p.68)
• Alternative sources (renewable, from biomass): biodiesel, bioethanol, biogas. (p.70)

2.2 Homologous Series

• Homologous series characteristics: same general formula, same functional group, same chemical properties, consecutive members differ by CH₂ (14), gradual change in physical properties. (p.71)
• General formulae: alkane C_nH_2n+2; alkene C_nH_2n; alkyne C_nH_2n−2; alcohol C_nH_2n+1OH; carboxylic acid C_nH_2n+1COOH; ester C_mH_2m+1COOC_nH_2n+1. (p.71)
• Functional groups: alkane C–C single bond; alkene C=C; alkyne C≡C; alcohol hydroxyl (–OH); carboxylic acid carboxyl (–COOH); ester carboxylate (–COO–). (p.71)
• Root names: meth, eth, prop, but, pent, hex, hept, oct, non, dec (1–10 carbons). (p.72)
• Suffixes: alkane “ane”; alkene “ene”; alkyne “yne”; alcohol “ol”; carboxylic acid “oic”; ester “oate”. (p.72)
• Alkanes are saturated hydrocarbons (C_nH_2n+2) with only single bonds. (p.73)
• Alkenes (C_nH_2n, n ≥ 2) contain a C=C double bond; ethene is the first member and is produced by ripening fruit. (p.74)
• Alkynes (C_nH_2n−2, n ≥ 2) contain a C≡C triple bond; ethyne is used for metal cutting. (p.75)
• Alcohol naming: replace the “e” of the alkane with “ol” (e.g. propan-1-ol). The hydroxyl group is not the same as the hydroxide ion. (p.76)
• Carboxylic acid naming: replace “e” with “oic acid”, e.g. methanoic acid HCOOH (ant bites), ethanoic acid CH₃COOH (vinegar). First value of n is 0. (p.77)
• Physical properties of alkanes, alkenes and alkynes: insoluble in water, soluble in organic solvents, do not conduct electricity, low melting/boiling points that increase with molecular size, less dense than water. (p.78)
• Alcohols and carboxylic acids have relatively high boiling points; solubility in water decreases as molecule size increases. (p.79)

2.3 Chemical Properties

• Alkanes are unreactive because C–C and C–H bonds are strong; they undergo combustion and substitution. (p.80)
• Complete combustion: CH₄ + 2O₂ → CO₂ + 2H₂O. Incomplete combustion produces soot (C), poisonous CO and water. (p.80)
• Substitution with halogens needs UV light; hydrogen atoms are replaced one by one (CH₄ → CH₃Cl → CH₂Cl₂ → CHCl₃ → CCl₄). (p.81)
• Alkenes are more reactive due to the double bond: combustion, addition and addition polymerisation. Alkenes burn with a sootier flame than alkanes because of a higher percentage of carbon by mass. (p.82)
• Hydrogenation: C_nH_2n + H₂ → C_nH_2n+2 (Ni catalyst, 180 °C). Halogenation: ethene decolourises bromine water (C₂H₄ + Br₂ → C₂H₄Br₂). (p.83)
• Addition of HBr: C₂H₄ + HBr → C₂H₅Br. Hydration: C₂H₄ + H₂O → C₂H₅OH (H₃PO₄, 300 °C, 60 atm). (p.84)
• Alkenes decolourise acidified KMnO₄; two –OH groups add across the double bond (ethene → ethane-1,2-diol). (p.84)
• Addition polymerisation: ethene forms polythene (200 °C, 1200 atm). (p.85)
• Alkenes and alkanes can be distinguished by bromine water and acidified KMnO₄: alkenes decolourise both, alkanes do not. (p.88)
• %C by mass: propane 81.82%; propene 85.71%. Greater %C gives a sootier flame. (p.87)
• Ethanol is prepared by fermentation of glucose (zymase enzyme): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂, and by hydration of ethene. (p.88)
• Fermentation product is purified by fractional distillation (ethanol collected at 78 °C); limewater tests for CO₂. (p.89)
• Alcohols burn with a blue flame without soot: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. (p.90)
• Oxidation of alcohols gives carboxylic acids: C₂H₅OH + 2[O] → CH₃COOH + H₂O. Acidified KMnO₄ goes colourless; acidified K₂Cr₂O₇ turns orange to green. (p.91)
• Dehydration of alcohols over porcelain chips/Al₂O₃ removes water to form alkenes: C₂H₅OH → C₂H₄ + H₂O. (p.91)
• Alkene from dehydration burns with a yellow sooty flame and decolourises bromine water and acidified KMnO₄. (p.92)
• Reflux (Liebig condenser upright) ensures ethanol reacts completely with the oxidising agent. (p.94)
• Ethanoic acid is a weak acid; it reacts with bases, metal carbonates and metals to form salts (e.g. 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂; 2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂). (p.95)
• Esterification: carboxylic acid + alcohol → ester + water, with concentrated H₂SO₄ catalyst. (p.95)
• Ethyl ethanoate is a colourless, sweet-smelling liquid that is insoluble in water and floats on it. (p.96)
• Esters: general formula C_mH_2m+1COOC_nH_2n+1; the fragrant smell of flowers and fruits is mostly due to esters. (p.97)
• Ester naming: first part from the alcohol (“ol” → “yl”), second part from the acid (“oic acid” → “oate”), e.g. ethyl ethanoate. (p.98)
• Physical properties of esters: neutral, sweet fruity smell, insoluble in water, low density, easily vaporise, simple esters are colourless liquids. (p.99)

2.4 Isomers and IUPAC Naming

• Isomers have the same molecular formula but different structural formulae. Chain isomerism: different carbon chain arrangement. Position isomerism: different position of the functional group. (p.101)
• Isomers have the same chemical properties but different physical properties; more branches means lower melting and boiling points. (p.101)
• Alkane isomers are chain isomers only; alkene, alkyne and alcohol isomers include chain and position isomers. (p.101)
• Name = prefix (branch) + root + suffix. Alkyl groups: methyl (–CH₃), ethyl (–C₂H₅), propyl (–C₃H₇). Use “–” between number and name, “,” between numbers. (p.102)
• Steps: identify longest chain (containing the functional group), identify branches, number the chain so the functional group/branch gets the lowest number, state positions and names. Examples: 2,2-dimethylpropane, 3-methylbut-1-ene. (p.103)
• Examples: 3-methylbut-1-yne; 2-methylpropan-2-ol. (p.104)
• Methane, ethane and propane have no isomers; isomerism in alkanes begins with butane. Propanol has 2 isomers; butanol has 4. (p.105)
• Alkanes are fuels and petrochemical raw materials (ethane, butane, LPG). Alkenes are raw materials for polythene, PVC, polystyrene and synthetic rubber. (p.106)
• Uses of alcohol: fuel (gasohol), solvent (paint, perfume), antiseptics and medicine, raw material for vinegar and explosives. (p.107)
• Uses of carboxylic acids: ethanoic acid as preservative in sauces; methanoic acid to coagulate latex; fatty acids for soap; polyester and nylon. Misuse of alcohol harms the liver, brain and foetus. (p.108)
• Uses of esters: food flavourings (methyl butanoate = apple, ethyl butanoate = pineapple, pentyl ethanoate = banana), perfumes, solvents, soap, polyester. (p.109)