Organic chemistry flashcards

Topic 4: Organic chemistry

Homologous series

A family with the same general formula and functional group, similar chemical properties and a trend in physical properties; each member differs by CH₂.

Isomers

Compounds with the same molecular formula but different structural formulae. A bent chain is not a new isomer.

Crude oil fractions, top to bottom, with a use for each

Refinery gases: bottled gas. Gasoline: petrol. Kerosene: aircraft fuel. Diesel: lorries, trains. Fuel oil: ships, power stations. Bitumen: roads. Going down: higher boiling point, more viscous, darker.

Complete vs incomplete combustion

Complete (plenty of oxygen): CO₂ and H₂O. Incomplete: CO and/or C (soot). CO is poisonous: it reduces the blood’s capacity to carry oxygen.

Nitrogen oxides vs sulfur dioxide from engines and power stations

Nitrogen oxides: N₂ and O₂ from the air react at high temperature. Sulfur dioxide: sulfur impurities in the fuel. Both cause acid rain.

Cracking: products, conditions and why it is done

Long-chain alkane → shorter alkane + alkene. Silica or alumina catalyst, 600–700 °C. Supply of long-chain fractions exceeds demand; demand for short-chain fractions such as gasoline exceeds supply.

Addition vs substitution

Alkenes add (one product), e.g. C₂H₄ + Br₂ → C₂H₄Br₂. Alkanes substitute in UV light (two products, one is HX), e.g. C₃H₈ + Cl₂ → C₃H₇Cl + HCl.

Test to tell an alkene from an alkane

Bromine water: an alkene decolourises it (orange → colourless); an alkane leaves it orange.

Making ethanol: hydration of ethene vs fermentation (Paper 2 only)

Hydration: C₂H₄ + H₂O → C₂H₅OH; phosphoric acid catalyst, about 300 °C, 60–70 atm. Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂; yeast enzymes, about 30 °C, absence of air.

Making an ester, with an example (Paper 2 only)

Alcohol + carboxylic acid ⇌ ester + water, with an acid catalyst. Ethanol + ethanoic acid → ethyl ethanoate, CH₃COOC₂H₅. Esters are used in food flavourings and perfumes.

Addition polymer

Many monomers joined as the C=C opens. The repeat unit has only single bonds in the backbone and extension bonds through the brackets.

Addition vs condensation polymerisation

Addition gives one product only. Condensation also gives water — e.g. a dicarboxylic acid + a diol → polyester + water (Paper 2 only).