Organic
Chemistry

• Crude oil is heated until it vaporises and fed into a fractionating column, which is hot at the bottom and cool at the top
• Vapours rise up the column and condense when they cool to a temperature at or below their boiling point
• Fractions with the longest chains (highest boiling points) condense near the bottom; fractions with the shortest chains (lowest boiling points) condense near the top and leave as a gas
• Each fraction is still a mixture of hydrocarbons with similar (not identical) chain lengths and boiling points

Trends from bottom to top of the column:

• Chain length: decreases
• Boiling point: decreases
• Volatility (how easily it evaporates): increases
• Viscosity (how easily it flows) and colour/sootiness of flame when burned: decreases

Complete combustion (excess oxygen):

Incomplete combustion (limited oxygen):

• Complete combustion: blue flame, no soot, produces CO₂ + H₂O
• Incomplete combustion: yellow/orange flame, soot, produces CO (poisonous) or C
• Carbon monoxide (CO) is dangerous — it binds to haemoglobin and prevents oxygen transport
• Used as fuels: methane = natural gas, propane/butane = camping gas, octane = petrol

• A hydrogen atom on the alkane is replaced (substituted) by a halogen atom
• UV light is needed to start (initiate) the reaction — does NOT work in the dark
• Further substitution is possible: CH₃Cl → CH₂Cl₂ → CHCl₃ → CCl₄
• Works with Cl₂ (chlorine) or Br₂ (bromine)
• Products: halogenoalkane + hydrogen halide (HCl or HBr)

• Cracking breaks long-chain alkanes into shorter, more useful molecules
• Two types: thermal cracking (high temp, high pressure) and catalytic cracking (lower temp, catalyst)
• Products: shorter alkanes (for petrol) + alkenes (for polymers and chemicals)
• Why? Long alkanes from crude oil are less useful — cracking converts them to petrol and alkenes
• The alkene products are very useful — they're used to make plastics, ethanol, and other chemicals

• The C=C double bond breaks and two H atoms add across it
• Product is an alkane (now fully saturated)
• Industrial use: converts unsaturated vegetable oils (liquids) into saturated fats (solids) — this is how margarine is made!
• Nickel catalyst, temperature around 150°C

• Bromine water (orange/brown) is decolourised → colourless
• This is the TEST for alkenes — alkanes do NOT do this at room temperature
• No catalyst needed
• Product: 1,2-dibromoethane (a dihalogenoalkane)

• Steam (H₂O) adds across the double bond to form ethanol (an alcohol)
• Conditions: phosphoric acid catalyst (H₃PO₄), high pressure (60–70 atm), ~300°C
• This is the industrial (non-renewable) route to ethanol — starting material is ethene from crude oil
• Compare to fermentation: fermentation uses glucose (renewable) but is slower

• Many small monomer molecules join together to form one large polymer chain
• The C=C double bond opens up and links to neighbouring monomers — no atoms are lost
• Examples: poly(ethene) = plastic bags & bottles; poly(propene) = ropes & crates; PVC = pipes; PTFE = non-stick coating
• Name the polymer: "poly" + (monomer name). E.g. ethene → poly(ethene)

• Alcohols burn with a clean blue flame and produce CO₂ + H₂O
• Ethanol is used as a biofuel — it is renewable (made from plant sugars)
• Balance by first balancing C, then H, then O

• CIE 5070 syllabus (11.6.1a): ethanol is manufactured by fermentation of aqueous glucose at 25–35°C, using yeast, in the absence of oxygen
• Yeast contains enzymes that convert glucose into ethanol and carbon dioxide
• Too hot (>35°C) → enzymes denature and stop working; too cold → reaction is too slow
• Fermentation stops naturally once the ethanol concentration reaches about 15% — it kills the yeast
• The mixture is then distilled to increase (concentrate) the ethanol content

• CIE 5070 syllabus (11.7.2a): the oxidising agent specified is acidified aqueous potassium manganate(VII), KMnO₄
• Colour change: KMnO₄ is purple → colourless as it is reduced while the alcohol is oxidised
• [O] represents "oxygen from the oxidising agent" — shorthand used for oxidation equations
• Bacterial oxidation (11.7.2b): in vinegar production, bacteria in the air oxidise ethanol in wine/cider to ethanoic acid — this is also why an open bottle of wine turns sour

• A water molecule (H₂O) is removed from the alcohol
• A C=C double bond forms → product is an alkene
• Concentrated H₂SO₄ (sulphuric acid) acts as catalyst, heated to ~170°C
• Aluminium oxide (Al₂O₃) can also be used as the catalyst
• This is the reverse of the hydration of alkenes!

• Alcohol + carboxylic acid → ester + water
• The ⇌ sign means it is a reversible reaction
• Concentrated H₂SO₄ is the catalyst (not used up)
• Esters have sweet, fruity smells — used in perfumes and food flavourings (e.g. pear drops)
• Naming: first word = alcohol part (ethanol → ethyl); second word = acid part (ethanoic acid → ethanoate)

• Acid + reactive metal → salt + hydrogen gas
• Test for H₂: burning splint makes a squeaky pop
• Reacts more slowly than mineral acids (HCl, H₂SO₄) because it is a weak acid
• Salt is named: metal name + carboxylate. Mg + ethanoic acid → magnesium ethanoate

• Acid + metal oxide → salt + water
• Acid + metal hydroxide → salt + water (neutralisation)
• Black copper(II) oxide dissolves in warm acid → blue-green copper ethanoate solution
• Universal indicator turns from red (acid) to green (neutral) as reaction proceeds

• Acid + carbonate → salt + water + carbon dioxide
• Visible bubbles of CO₂ are produced
• Test for CO₂: bubbles turn limewater milky
• Works with Na₂CO₃ (sodium carbonate), CaCO₃ (marble/limestone/chalk), NaHCO₃ (baking soda)

• Carboxylic acid + alcohol → ester + water
• Reversible reaction (⇌) — equilibrium is established
• Concentrated H₂SO₄ is the catalyst
• Esters have distinctive fruity smells — used in food flavouring and perfumes
• Naming: alcohol part first (ethyl), acid part second (ethanoate) → ethyl ethanoate

• Carboxylic acid + alcohol → ester + water
• The reaction is reversible (⇌) — an equilibrium is reached
• Concentrated sulphuric acid (H₂SO₄) is the catalyst — it speeds up the reaction but is not used up
• The mixture is warmed gently — too much heat favours decomposition back to reactants
• To improve yield: remove water as it forms, use excess of one reactant, or use a drying agent
• The –OH from the acid and –H from the alcohol combine to form the water molecule

• First word = from the alcohol. Change -ol to -yl (ethanol → ethyl)
• Second word = from the acid. Change -ic acid to -ate (ethanoic acid → ethanoate)
• To work backwards: split at the –COO– bond. Left side (–CO–) = acid part; right side (–O–) = alcohol part

Acid hydrolysis (with dilute acid + water):

Alkaline hydrolysis / saponification (with NaOH):

• Hydrolysis = splitting with water. The ester bond (–COO–) is broken
• Acid hydrolysis is reversible (⇌) — gives the carboxylic acid and alcohol back
• Alkaline hydrolysis is irreversible — the base reacts with the acid product to form a carboxylate salt
• Saponification is the alkaline hydrolysis of fats/oils (esters of glycerol) to make soap
• This is the basis of soap-making: fat + NaOH → soap (sodium salt of fatty acid) + glycerol

• Perfumes: esters have pleasant fruity/floral smells; evaporate easily from skin
• Food flavourings: artificial fruit flavours in sweets, drinks, yoghurt
• Solvents: ethyl ethanoate dissolves paints, varnishes, nail polish
• Plasticisers: added to PVC to make it flexible
• Biodiesel: plant oils (triglycerides = esters) are converted to methyl esters by reacting with methanol

• A diol (two –OH groups) reacts with a dicarboxylic acid (two –COOH groups)
• An ester linkage (–COO–) forms each time, and a water molecule is released
• Called condensation polymerisation because a small molecule (H₂O) is lost each time monomers join
• Unlike addition polymerisation (alkenes), atoms ARE lost as water
• Example: Terylene / PET (polyethylene terephthalate) — used in clothing, plastic bottles, and synthetic fibres

• A dicarboxylic acid (–COOH at both ends) reacts with a diamine (–NH₂ at both ends)
• An amide linkage (–CO–NH–) forms between each pair of monomers, releasing water
• Nylon is a synthetic polyamide — used in fabrics, ropes, and carpets
• The repeat unit alternates: acid section — amide link — amine section — amide link

• A dicarboxylic acid reacts with a diol (–OH at both ends)
• An ester linkage (–COO–) forms between each pair of monomers, releasing water
• PET (a polyester, sold as Terylene/Dacron) is used for clothing fibres and plastic bottles
• PET can be broken back down into its monomers and re-polymerised — this is the basis of PET recycling

• Proteins are natural polyamides built from amino acid monomers
• Each amino acid has the general structure H₂N–CH(R)–COOH, with an amine group and a carboxylic acid group on the same carbon
• The R group ("side-chain") differs between amino acids — this is what makes proteins so varied
• Amino acids join by condensation: the –COOH of one reacts with the –NH₂ of the next, forming an amide link and releasing water — exactly like nylon formation

• Landfill: most plastics are not biodegradable, so they persist in landfill sites for a very long time
• Ocean accumulation: plastic waste that reaches the sea builds up and harms marine life
• Burning: incinerating some plastics (e.g. PVC) releases toxic gases
• Recycling: PET and other polymers can be collected, broken down, and re-polymerised or reprocessed, reducing the need for new plastic