Chemistry • Year 12 • Module 7 • Lesson 2
IUPAC Nomenclature II: Functional Group Classes & Isomers
Lock in the structural signatures, suffixes/prefixes, and isomer vocabulary for all eight functional group classes covered in this lesson.
1. Term–definition match
Match each term in the left column to the correct definition. Write the term in the right-hand column. Terms: aldehyde, ketone, carboxylic acid, ester, amine, amide, haloalkane, structural isomer, chain isomer, position isomer, functional group isomer, primary alcohol. 12 marks
| # | Definition | Matching term |
|---|---|---|
| 1.1 | A compound with the structural formula R–CHO; the carbonyl carbon is terminal and has a hydrogen directly bonded to it. Suffix: -al. | |
| 1.2 | A compound with R–CO–R′; the carbonyl carbon is internal, flanked by two other carbons. Suffix: -one. | |
| 1.3 | A compound with R–COOH; terminal carbonyl plus a hydroxyl group on the same carbon. Suffix: -oic acid. | |
| 1.4 | Named as alkyl alkanoate; contains a –COO– linkage; the alkyl part (from the alcohol) is written first. | |
| 1.5 | A compound containing nitrogen bonded to one or more alkyl groups; a weak base because the lone pair on N is freely available. Suffix: -amine. | |
| 1.6 | Contains a –CONH2 group; neutral because the N lone pair is delocalised into the adjacent C=O. Suffix: -amide. | |
| 1.7 | Contains a halogen atom (F, Cl, Br, or I) bonded to a carbon chain; named with a prefix (fluoro-, chloro-, bromo-, iodo-) and a locant. | |
| 1.8 | Compounds that share the same molecular formula but have different structural arrangements of atoms. | |
| 1.9 | A pair of structural isomers with the same functional group and same molecular formula, but a different carbon skeleton (degree of branching). | |
| 1.10 | A pair of structural isomers with the same functional group and same carbon skeleton, but the functional group is attached to a different carbon. | |
| 1.11 | A pair of structural isomers with the same molecular formula but entirely different functional groups (e.g. an aldehyde and a ketone). | |
| 1.12 | An alcohol in which the carbon bearing the –OH group is bonded to exactly one other carbon. Classification determined by counting carbon neighbours of C–OH only. |
2. True or false — with correction
Circle T or F for each statement. If false, write the corrected version on the line provided. 10 marks (1 T/F + 1 correction)
2.1 Propanal and propanone are position isomers because the C=O group is at a different position on the same three-carbon chain. T / F
2.2 The IUPAC name for CH3COOC2H5 is ethyl ethanoate (alkyl group written first). T / F
2.3 Amides are weak bases because the nitrogen atom contains a lone pair that accepts H+ from acids, just like amines. T / F
2.4 The suffix –al always indicates an aldehyde, and a locant is never written for the aldehyde carbon because it is always C1. T / F
2.5 Butane (CH3CH2CH2CH3) and 2-methylpropane (CH3CH(CH3)CH3) are functional group isomers because they share the formula C4H10. T / F
3. Fill in the blanks — IUPAC naming rules
Complete the paragraph using the word bank below. Each word is used once. 10 marks
Word bank:
alkyl • alkanoate • locant • terminal • internal • delocalised • lowest • primary • halogen • -oic acid
When naming an alcohol, the chain is numbered from the end that gives the possible locant for the –OH group. An alcohol whose C–OH carbon is bonded to only one other carbon is classified as a alcohol. An aldehyde has its C=O group at the carbon, so no is needed. A ketone has its C=O group in an position between two carbon atoms. A carboxylic acid always uses the suffix and is also always at C1. An ester is named as + , with the part derived from the alcohol coming first. An amide is neutral because the lone pair on nitrogen is into the adjacent C=O group. Haloalkanes are named using the as a prefix (fluoro-, chloro-, bromo-, or iodo-) with a locant.
4. Function recall
Answer each question in 1–2 sentences using precise lesson vocabulary. 8 marks (2 each)
4.1 Explain why a locant is always written for an alcohol but is never written for an aldehyde or carboxylic acid.
4.2 Describe the key structural difference between propan-1-ol and propan-2-ol that makes one a primary alcohol and the other a secondary alcohol.
4.3 State what the terms ‘chain isomers’, ‘position isomers’, and ‘functional group isomers’ all have in common before they differ.
4.4 Explain why amines are weak bases while amides are neutral, referring to the lone pair on nitrogen in each case.
5. Build a concept map
Draw labelled arrows between the six terms to show how they connect. Each arrow must carry a linking phrase (e.g. “is a type of”, “uses suffix”, “is identified by”). Aim for at least 6 labelled arrows. 6 marks
Terms: functional group • IUPAC suffix/prefix • structural isomer • same molecular formula • carbon skeleton • locant.
Q1 — Term–definition match
1.1 aldehyde • 1.2 ketone • 1.3 carboxylic acid • 1.4 ester • 1.5 amine • 1.6 amide • 1.7 haloalkane • 1.8 structural isomer • 1.9 chain isomer • 1.10 position isomer • 1.11 functional group isomer • 1.12 primary alcohol.
Q2 — True / false
2.1 False. Propanal and propanone are functional group isomers. Both have the formula C3H6O but propanal is an aldehyde (terminal C=O with H) and propanone is a ketone (internal C=O between two carbons) — entirely different functional groups, not different positions of the same group.
2.2 True. CH3COOC2H5: ethanoate (from CH3COO–, the acid part) + ethyl (from –OC2H5, the alcohol part). Alkyl first → ethyl ethanoate.
2.3 False. Amides are neutral, not weak bases. The lone pair on the amide nitrogen is delocalised by resonance into the adjacent C=O and is not available to accept a proton. Amines (R–NH2) have an undelocalised lone pair that freely accepts H+ and are weak bases.
2.4 True. The aldehyde C=O is always at C1, so there is only one possible arrangement and no locant is required.
2.5 False. Butane and 2-methylpropane are chain isomers, not functional group isomers. Both are alkanes (same functional group class); only the shape of the carbon skeleton differs (straight vs branched).
Q3 — Cloze answers (in order)
lowest • primary • terminal • locant • internal • -oic acid • alkyl • alkanoate • delocalised • halogen.
Q4.1 — Locants for alcohols vs. aldehydes/acids
Alcohols need a locant because the –OH group can be placed at different positions along the chain (e.g. C1 or C2), giving structurally different compounds with different properties. Aldehydes and carboxylic acids do not need a locant because by definition their functional carbon (C=O + H for aldehyde; C=O + OH for acid) is always C1 at the chain terminus — there is only one possible position.
Q4.2 — Primary vs. secondary alcohol classification
In propan-1-ol, the carbon bearing the –OH group (C1) is bonded to only one other carbon (C2) → primary. In propan-2-ol, the carbon bearing the –OH (C2) is bonded to two other carbons (C1 and C3) → secondary. Classification counts only carbon neighbours of C–OH; H atoms and the O atom are ignored.
Q4.3 — What all structural isomers share
All structural isomers share the same molecular formula (same atoms, same count) but differ in the structural arrangement of those atoms. The difference can be in the carbon skeleton shape (chain isomers), the position of the functional group (position isomers), or the type of functional group itself (functional group isomers).
Q4.4 — Amine (base) vs. amide (neutral)
In an amine (R–NH2), the lone pair on nitrogen is not delocalised and is freely available to accept a proton from an acid → weak base. In an amide (R–CONH2), the lone pair on nitrogen is delocalised by resonance into the adjacent C=O bond — it is spread across the C–N region and cannot accept H+ → neutral.
Q5 — Sample concept map connections
Acceptable arrows include: functional group → is identified by → IUPAC suffix/prefix; IUPAC suffix/prefix → may include → locant; locant → specifies position on → carbon skeleton; structural isomer → requires → same molecular formula; structural isomer → may differ in → carbon skeleton; structural isomer → may differ in → functional group. Award 1 mark per biologically/chemically valid labelled arrow (up to 6).