HSC Chemistry organic chemistry (Module 7): 2026 guide

What Module 7 asks

HSC Chemistry Module 7 (Organic Chemistry) is the most memorisation-heavy module in the course, typically accounting for a substantial share of marks in recent papers (NESA does not publish fixed module weightings). Students who treat organic as a system of named functional groups and predictable reactions do well; students who try to derive everything from first principles run out of time.

The content is structured around functional groups and the reactions that interconvert them.

Functional groups

Memorise these. Strong students can draw each from memory in under 5 seconds.

Naming organic compounds (IUPAC)

The rules:

1. Identify the longest carbon chain containing the highest-priority functional group. The chain length gives the prefix: meth (1), eth (2), prop (3), but (4), pent (5), hex (6), hept (7), oct (8).
2. Number the carbons from the end nearest the highest-priority functional group.
3. Add the appropriate suffix and locant (number) for the main functional group.
4. Identify substituents (methyl, ethyl, halogen, etc.) and add as prefixes with locants.

Worked example: name CH3-CH(OH)-CH2-CH3.

• Longest chain: 4 carbons (butane).
• Functional group: OH (alcohol, suffix -ol).
• Numbering: closest to OH, so the OH carbon is 2.
• Name: butan-2-ol.

Worked example: name CH3-COOCH2CH3.

• The compound is an ester (CH3-COO-CH2CH3).
• The acyl part (left of -COO-) is from ethanoic acid: name the alkyl part attached to the oxygen first (ethyl), then the acyl part (ethanoate).
• Name: ethyl ethanoate.

Reaction types

Substitution

Alkanes + halogens (Cl2, Br2) in the presence of UV light yield haloalkanes:

Mechanism is free-radical. Reactivity: F > Cl > Br > I.

Addition

Alkenes (and alkynes) undergo addition. The double bond opens and reagent adds across the carbons.

Hydrogenation: alkene + H2 (with Ni catalyst) → alkane.
Halogenation: alkene + Br2 → 1,2-dibromoalkane.
Hydration: alkene + H2O (with H2SO4 catalyst) → alcohol.
Hydrohalogenation: alkene + HX → haloalkane (Markovnikov's rule: H goes to the carbon with more H, X to the carbon with fewer H).

Worked example:

Oxidation

Alcohols are oxidised to aldehydes (primary alcohol with limited oxidiser) or ketones (secondary alcohol). Further oxidation of an aldehyde gives a carboxylic acid.

Common oxidising agents: KMnO4 (potassium permanganate), K2Cr2O7 (potassium dichromate).

(ethanol → ethanal → ethanoic acid)

Tertiary alcohols (no H on the carbon bearing OH) cannot be oxidised by these reagents.

Esterification

A carboxylic acid plus an alcohol, with H2SO4 catalyst, produces an ester plus water:

(ethanoic acid + ethanol → ethyl ethanoate + water)

This is a reversible reaction at equilibrium. Excess of one reagent (or removal of water) shifts the equilibrium toward the ester.

Esters give characteristic fruity smells (banana, pineapple, pear) and are used in fragrances and flavourings.

Polymerisation

Addition polymerisation: alkene monomers join via opening of the C=C double bond. No small molecule is lost.

Common addition polymers: polyethylene (from ethene), polypropylene (from propene), polyvinyl chloride (from chloroethene), polystyrene (from styrene).

Condensation polymerisation: monomers join with loss of a small molecule (usually water). Requires monomers with two reactive functional groups each.

Examples:

• Polyester (e.g. PET): diol + dicarboxylic acid → polyester + water.
• Nylon (e.g. nylon-6,6): diamine + dicarboxylic acid → polyamide + water.

Hydrocarbons as fuels

Combustion of hydrocarbons:

Complete combustion (sufficient oxygen): $C_nH_m + (n + m/4) O_2 \rightarrow n CO_2 + m/2 H_2O$. Produces only CO2 and water.

Incomplete combustion (insufficient oxygen): produces CO (toxic) and/or soot (carbon particles).

Biofuels include bioethanol (from fermentation of sugars), biodiesel (from transesterification of vegetable oils). Strong responses evaluate the trade-offs - reduced fossil fuel use vs land use, ethical and economic concerns.

Common HSC Module 7 traps

Confusing aldehydes and ketones

Aldehyde has the -CHO at the end of the chain. Ketone has -C(=O)- in the middle. Different naming, different reactivity (aldehydes can be oxidised further; ketones cannot).

Forgetting Markovnikov's rule

For asymmetric alkenes plus HX, the H adds to the carbon with MORE H atoms; the X adds to the carbon with FEWER H atoms. This is the major product.

Naming errors with locants

Always number from the end nearest the highest-priority functional group. If both ends give the same locant for the main group, choose the numbering that gives lower locants to substituents.

Mixing up addition and condensation polymerisation

Addition: no small molecule lost. Condensation: water (or similar) released per bond formed.

Forgetting the H2SO4 catalyst in esterification

Many students write the reaction without the catalyst. Markers may not award the mark.

How Module 7 is examined

In the HSC Chemistry exam:

• Multiple choice. Identify a compound from its structure. Name an organic compound. Predict products of a reaction.
• Section II short questions (3-5 marks). Draw a structural formula. Write a balanced equation for a reaction. Identify functional groups.
• Section II extended response (6-9 marks). Multi-step synthesis (e.g. propose a route from ethene to ethyl ethanoate). Spectra interpretation. Polymer evaluation.

Practice strategy

For HSC Chemistry Module 7:

• Term 3. Memorise functional groups and the standard reactions cold. Draw each from memory.
• Term 4. Past papers focused on Module 7. Multi-step synthesis questions repeat patterns; spot them.

Build a flowchart of how the functional groups interconvert (alkene → alcohol → aldehyde → carboxylic acid; carboxylic acid + alcohol → ester). This single diagram answers most of the synthesis questions.

Check your knowledge

A mix of definitional, calculation/explanation, and exam-style multi-part questions covering this topic. Aim to answer all under exam conditions, then check against the solutions block.

1. Define the term structural isomer and draw the three structural isomers of $C_4H_{10}O$ that are alcohols, naming each using IUPAC nomenclature. (4 marks)
2. (a) Write the balanced equation for the complete combustion of octane ($C_8H_{18}$), a major component of Australian unleaded petrol. (b) Calculate the volume of $CO_2$ at standard laboratory conditions (25 degrees C, 100 kPa, $V_m = 24.79$ L mol$^{-1}$) produced when 5.00 L of liquid octane (density 0.703 g mL$^{-1}$, $M = 114.23$ g mol$^{-1}$) is combusted. (5 marks)
3. The reaction $CH_3CH_2OH + CH_3COOH \rightleftharpoons CH_3COOCH_2CH_3 + H_2O$ is set up by mixing 0.100 mol ethanol with 0.100 mol ethanoic acid plus a few drops of concentrated $H_2SO_4$ in a sealed 1.00 L vessel. At equilibrium the vessel contains 0.667 mol ethyl ethanoate. (a) Calculate $K_c$. (b) State two ways the yield could be increased and justify each using Le Chatelier's principle. (c) Explain the role of the $H_2SO_4$. (6 marks)
4. Predict the major organic product of each of the following reactions, naming it and identifying the reaction type. (a) But-2-ene + HBr. (b) Propan-2-ol heated under reflux with acidified $K_2Cr_2O_7$. (c) Propan-1-ol + ethanoic acid with conc. $H_2SO_4$. (d) Ethene + steam at 300 degrees C with phosphoric acid catalyst. (8 marks)
5. (a, 3) Distinguish addition polymerisation from condensation polymerisation, with a balanced equation showing one repeat unit for polyethylene and one repeat unit for nylon-6,6 (formed from hexamethylenediamine and hexanedioic acid). (b, 3) Compare the chemical recyclability of these two polymers, justifying with reference to bond types. (c, 2) Identify one Australian context where condensation polymers have replaced traditional materials. (8 marks)
6. Compound X has the molecular formula $C_3H_6O$ and reduces acidified $K_2Cr_2O_7$ from orange to green. Compound Y has the same formula but does not react. (a) Identify a possible identity for X and Y. (b) Draw their structural formulas. (c) Write a balanced equation for the oxidation of X by acidified dichromate, generating a carboxylic acid. (5 marks)
7. Compare and contrast the substitution of chlorine with methane (under UV) and the addition of chlorine with ethene (in the dark). Address (a) the mechanism, (b) the structural feature in each hydrocarbon that determines the reaction type, and (c) the product mixture. (6 marks)
8. Australia produces approximately 9 billion litres of bioethanol annually from sugar-cane residue. (a) Write the balanced equation for fermentation of glucose to ethanol. (b) Discuss the renewability of bioethanol compared with fossil-derived ethanol (produced from petrochemical ethene plus water), referring to feedstock, $CO_2$ life-cycle, and land-use. (c) Evaluate the use of bioethanol-petrol blends (e.g. E10) as a transport fuel in Australia, addressing engine compatibility, emissions and Indigenous land-use considerations. Write a coherent extended response of approximately 200 to 300 words. (7 marks)