Coaching Centre
Organic chemistry review
A summary of all of Module 7 Organic Chemistry, how the topics connect, key words, and a mixed HSC-style test covering naming, isomers, properties, hydrocarbon and alcohol reactions, enthalpy of combustion, esters, soaps and detergents, reaction pathways and polymers.
Use this page to check the whole module. Read the summary, make sure you can explain every key word, then do the test under exam conditions before checking any answers.
Module summary
| Topic | What you need to know |
|---|---|
| 7A Naming hydrocarbons | Find the longest chain containing the C=C or C≡C; number from the end that gives the multiple bond (then substituents) the lowest locants; list substituents alphabetically with di-, tri- prefixes; commas between numbers, hyphens between numbers and words. Alkanes CₙH₂ₙ₊₂, alkenes CₙH₂ₙ, alkynes CₙH₂ₙ₋₂; cycloalkanes CₙH₂ₙ. |
| 7B Isomers and shape | Structural isomers: same molecular formula, different connectivity. Chain, position and functional group isomers. Molecular, structural, condensed and skeletal formulae. Tetrahedral 109.5° (single bonds), trigonal planar 120° (C=C), linear 180° (C≡C). No rotation about C=C. |
| 7C Functional groups | Suffixes and priority: carboxylic acid (-oic acid) > amide (-amide) > aldehyde (-al) > ketone (-one) > alcohol (-ol) > amine (-amine); haloalkanes use prefixes (chloro-). Esters are named alkyl alkanoate. Alcohols are primary, secondary or tertiary. |
| 7D Properties | Boiling point rises with chain length (dispersion forces) and falls with branching (less contact). Polar groups add dipole–dipole; –OH, –COOH, –NH₂, –CONH₂ add hydrogen bonding. Small polar molecules are water soluble; solubility falls as the hydrocarbon chain grows. |
| 7E Hydrocarbon reactions | Alkenes undergo addition: H₂ (Ni), X₂, HX, H₂O (acid catalyst). Bromine water decolourises with alkenes instantly (test for unsaturation); alkanes react only by substitution in UV light. Unsymmetrical alkenes give two products. |
| 7F Hydrocarbons and society | Fractional distillation and cracking of crude oil; uses of fractions. Toxicity and flammability of hydrocarbons; benzene is carcinogenic. Environmental impacts: spills, microplastics, greenhouse gases; safe handling and disposal. |
| 7G Combustion of alcohols | Complete combustion → CO₂ + H₂O. $\Delta_c H = -\dfrac{mc\Delta T}{n}$ (heat from fuel = heat gained by water). Experimental values are smaller than data values due to heat loss and incomplete combustion. Each extra CH₂ adds about −650 kJ mol⁻¹. |
| 7H Alcohol reactions and production | Dehydration (conc. H₂SO₄) → alkene; substitution (HX) → haloalkane; oxidation with acidified Cr₂O₇²⁻ (orange → green) or MnO₄⁻: 1° → aldehyde (distil) → acid (reflux); 2° → ketone; 3° no reaction. Ethanol from fermentation (yeast, anaerobic, C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂) or hydration of ethene. Biofuels. |
| 7I Acids, bases and esters | Carboxylic acids are weak acids; amines are weak bases. Esterification: acid + alcohol ⇌ ester + water, conc. H₂SO₄ catalyst, reflux to avoid losing volatile chemicals; purify by washing with Na₂CO₃, separating and distilling. Amides from acid + amine. |
| 7J Soaps and detergents | Saponification: fat + NaOH → glycerol + soap. Surfactants have a polar (hydrophilic) head and non-polar (hydrophobic) tail and form micelles around grease. Soap forms scum in hard water and fails in acid; anionic, cationic and non-ionic detergents have different heads and uses. |
| 7K Reaction pathways | Work backwards from the target; draw a flow chart with intermediates and reagents/conditions on each arrow. Overall yield = product of step yields. Choose routes by yield, atom economy, cost, safety and waste. |
| 7L Addition polymers | C=C monomers; initiation, propagation, termination. LDPE branched (soft, 0.92 g/cm³) vs HDPE linear (rigid, crystalline). PVC (C–Cl dipoles, plasticisers), polystyrene (bulky ring, rigid), PTFE (strong C–F, inert, non-stick). |
| 7M Condensation polymers | Two functional groups per monomer; water lost per link. Polyesters (diacid + diol: PET; PLA from lactic acid) and polyamides (diacid + diamine: nylon 6,6; nylon 6) with hydrogen bonds between chains. Proteins and cellulose are natural condensation polymers. |
Putting it together
The whole module rests on one idea: the functional group decides how a molecule behaves. The carbon skeleton and its name (7A–7C) tell you what you're dealing with. The functional group then sets the intermolecular forces, and so the boiling point and solubility (7D). It also sets the reactions: a C=C adds (7E, 7L), an –OH can be dehydrated, substituted or oxidised (7H), a –COOH condenses with –OH to make an ester (7I) or, with two of each, a polyester (7M). Put these reactions together and you can travel from crude oil or sugar to almost any molecule in the module (7K). Underneath it all is the practical side: how much energy fuels release (7G), how to reflux and purify a product (7I), and how the products we make, from soap to plastic, affect people and the environment (7F, 7J, 7M).
Key words
addition polymer · addition reaction · alcohol (primary, secondary, tertiary) · aldehyde · alkane · alkene · alkyne · amide · amine · biofuel · carboxylic acid · chain isomer · condensation polymer · cracking · dehydration · detergent · dipole–dipole force · dispersion force · enthalpy of combustion · ester · esterification · fermentation · fractional distillation · functional group · functional group isomer · haloalkane · homologous series · hydrogen bond · hydrophilic · hydrophobic · initiation · ketone · micelle · monomer · oxidation · polyamide · polyester · position isomer · propagation · reflux · repeating unit · retrosynthesis · saponification · saturated · structural isomer · substitution reaction · surfactant · termination · thermoplastic · unsaturated
Test yourself
What is the IUPAC name of CH₃CH(CH₃)CH₂CH(OH)CH₃?
The –OH gets the lowest locant: number from the right, giving pentan-2-ol with a methyl on C4.
Which pair are functional group isomers?
Both are C₃H₆O, one an aldehyde and one a ketone.
Which compound has the highest boiling point?
All have similar molar masses (72–74 g/mol). Carboxylic acids form two hydrogen bonds per pair of molecules (dimers), so propanoic acid boils highest (141 °C vs 117 °C for butan-1-ol).
A compound decolourises bromine water quickly and has the formula C₄H₈. Which could it be?
C₄H₈ could be an alkene or a cycloalkane; only the alkene reacts quickly with bromine water.
2-methylpropan-2-ol is warmed with acidified potassium dichromate. The mixture
A tertiary alcohol has no H on the carbon bearing the –OH, so it isn't oxidised.
In a spirit burner experiment, 0.52 g of ethanol heated 200 g of water by 15.0 °C. The experimental enthalpy of combustion is closest to
q = 200 × 4.18 × 15.0 = 12 540 J; n = 0.52 ÷ 46.07 = 0.01129 mol; ΔcH = −12.54 ÷ 0.01129 = −1111 kJ mol⁻¹.
Which statement about the esterification of ethanoic acid with ethanol is correct?
Excess reactant shifts the equilibrium right. A catalyst only speeds it up (although conc. H₂SO₄ also absorbs some water); reflux keeps volatile chemicals in the flask; Na₂CO₃ is used to remove acids.
Which part of a soap anion dissolves in grease?
The non-polar tail mixes with non-polar grease by dispersion forces; the ionic head stays in the water.
The polymer –[CH₂–CCl₂]ₙ– is made from
Put the C=C back between the two backbone carbons: CH₂=CCl₂, with both chlorines on C1.
Which monomer could form a polymer by itself through condensation?
It has both –NH₂ and –COOH, so it can form amide links at both ends (it's the amino acid alanine).
Name each functional group class on the map.
Classify each reaction.
Order these compounds from lowest to highest boiling point.
A molecule with a polar head and a non-polar tail is a . Ethanol made from sugars by yeast is produced by . Heating a reaction mixture with a vertical condenser so vapours return to the flask is called . The reaction of a fat with sodium hydroxide is . A polymer made from a diol and a diacid is a .
Starting from ethene and using any inorganic reagents, a student wants to make ethyl ethanoate. Construct a flow chart for the synthesis including reagents and conditions, explain why reflux is used in the final step, and evaluate the student's claim that "ethanol made from ethene is better for the environment than ethanol made by fermentation".
Flow chart. Ethene —(H₂O steam, H₃PO₄ catalyst, ~300 °C, 6–7 MPa)→ ethanol. Part of the ethanol —(acidified K₂Cr₂O₇, heat under reflux)→ ethanoic acid. Ethanoic acid + ethanol —(a few drops of conc. H₂SO₄, heat under reflux)→ ethyl ethanoate + water.
Reflux. Esterification is slow, so the mixture must be heated, but ethanol (78 °C) and ethyl ethanoate (77 °C) are volatile and flammable. A vertical condenser cools vapours so they condense and drip back into the flask: the mixture can be heated for a long time without losing reactants or product, and flammable vapour doesn't escape.
Evaluation. Hydration of ethene is fast, continuous and gives nearly pure ethanol with 100% atom economy, and it needs no farmland. However, ethene comes from cracking crude oil or natural gas, a non-renewable feedstock, and the process needs high temperature and pressure, so burning that ethanol adds fossil carbon to the atmosphere. Fermentation uses renewable sugars; the CO₂ released was recently absorbed by the plants, so it is closer to carbon neutral, although fertiliser, farm machinery and distillation all use energy, and land used for fuel crops can compete with food. On balance, the claim is not supported: for the environment, fermentation ethanol is generally better, especially when made from waste such as molasses (as at Sarina in Queensland), even though ethene hydration is more efficient as a chemical process.
Explain the trend in boiling points: butane −1 °C, butan-1-ol 117 °C, hexan-1-ol 157 °C. Refer to the intermolecular forces present.
Butane is non-polar, so only weak dispersion forces act between its molecules, and little energy is needed to separate them: it boils at −1 °C. Butan-1-ol has a similar size but its –OH group forms hydrogen bonds between molecules (as well as dipole–dipole and dispersion forces). Much more energy is needed to break these, so it boils 118 °C higher. Hexan-1-ol has the same hydrogen bonding but two extra CH₂ groups; its larger electron cloud and greater contact area give stronger dispersion forces, so it boils 40 °C higher than butan-1-ol.