The shape of the lesson
By the end of the lesson, learners can
- Stems, suffixes and prefixes: Draw molecules in the naming simulator and check your name against the generated one.
- Stem from the longest chain including the functional group.
- Suffix from the main group; halogens and alkyl groups are prefixes.
- Lowest locants; di/tri for repeats.
- Esters: alkyl + -oate.
One picture every idea returns to
Find the longest carbon chain containing the functional group; its length gives the stem (meth-, eth-, prop-, but-, pent-, hex-). The functional group gives the suffix (-ane, -ene, -ol, -al, -one, -oic acid, -nitrile, -amine) or a prefix (chloro-, bromo-, methyl-). Number the chain from the end that gives the lowest locants, list prefixes alphabetically, and use di-, tri- for repeats.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, A name that draws itself.. An IUPAC name is an instruction for drawing the molecule: how long the chain is, what is attached and where. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 30 min | Teach and check: Stems, suffixes and prefixes | Draw molecules in the naming simulator and check your name against the generated one. Project tab 2 of the lab (Organic chemistry lab, naming) and let a student drive it while the class predicts. | Rally Robin |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 15 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Stems, suffixes and prefixes, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Rally Robin
Pairs take turns to say one item each, back and forth: a definition, a unit, a step of the method. Keep it fast and oral; the point is retrieval, not writing.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Always find the longest chain, which may bend round a corner in a drawn structure; a “branch” at the end of a chain is just part of the chain. | Number from the end that gives the lowest locants, and in nitriles, acids and aldehydes the functional-group carbon is C1 and is included in the stem count. |
Naming organic compounds: worksheet
6 questions, 15 marks. Written in the style of the papers; no past paper question is reproduced.
Name: (a) CH3CH(OH)CH2CH3, (b) CH3COCH3, (c) HCOOCH3, (d) CH3CH2CH2COOH.
Draw structural formulae for (a) 2-methylpropan-1-ol, (b) pent-2-ene, (c) 1,2-dibromoethane.
A student names a compound 4-methylpentane. Explain the error and give the correct name.
A student names CH3CH2CH(CH2CH3)CH3 as 2-ethylbutane. Explain why this is wrong and give the correct name.
Name the ester formed from propanoic acid and methanol, and give its structural formula.
Name CH3CHClCH2Br and CH3CH2CH2NH2.
Answer key and marking notes
- (a) butan-2-ol.
- (b) propanone.
- (c) methyl methanoate.
- (d) butanoic acid.
- (a) (CH3)2CHCH2OH.
- (b) CH3CH=CHCH2CH3.
- (c) CH2BrCH2Br.
- The chain should be numbered from the other end to give the methyl group the lowest locant.
- Correct name: 2-methylpentane.
- The longest chain runs through the ethyl group: it has five carbons, not four.
- Correct name: 3-methylpentane.
- Methyl propanoate.
- CH3CH2COOCH3.
- 1-bromo-2-chloropropane (prefixes in alphabetical order).
- Propylamine (propan-1-amine).
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
What is the IUPAC name of (CH3)2CHCH2CH3?
- A2-methylbutane
- B3-methylbutane
- C2-ethylpropane
- Dpentane
What is the IUPAC name of C(CH3)4?
- A2,2-dimethylpropane
- B2-dimethylpropane
- C2,2-methylpropane
- Dtetramethylmethane
What is the IUPAC name of CH2=CHCH2CH3?
- Abut-1-ene
- Bbut-3-ene
- Cbut-2-ene
- Dbutane
What is the IUPAC name of CH3CH(OH)CH3?
- Apropan-2-ol
- Bpropan-1-ol
- Cpropan-2-one
- D1-methylethanol
What is the IUPAC name of CH3CH2COOH?
- Apropanoic acid
- Bethanoic acid
- Cpropanal
- Dpropanone
What is the IUPAC name of CH3CH2CH(CH3)CH(CH3)CH3?
- A2,3-dimethylpentane
- B3,4-dimethylpentane
- C2-ethyl-3-methylbutane
- D2,3-methylpentane
What is the IUPAC name of the ester CH3COOCH3?
- Amethyl ethanoate
- Bethyl methanoate
- Cmethyl methanoate
- Dpropanoic acid
Which compound is named correctly?
- ACH3CH2CN, propanenitrile
- BCH3CH2CH2CHO, butanone
- CCH3CHClCH3, 1-chloropropane
- DCH3CH2NH2, methylamine
Quiz key
The longest chain has four carbons (butane) with a methyl branch. Numbering from the end nearer the branch puts it on C2, giving 2-methylbutane. 3-methylbutane numbers from the wrong end; the rule is lowest locants. 2-ethylpropane misses the longest chain: an ethyl group on C2 of propane actually extends the chain to four carbons. Pentane is the unbranched isomer CH3(CH2)3CH3; it has the same molecular formula, C5H12, but a different structure.
The longest chain is three carbons (propane), and both methyl groups are on C2. Every branch needs its own locant and identical groups take di, so the name is 2,2-dimethylpropane. 2-dimethylpropane gives only one locant for two groups. 2,2-methylpropane leaves out di. Tetramethylmethane does not use the longest chain: the central carbon plus any two methyl carbons form a three-carbon chain.
The chain has four carbons and the C=C starts at C1 when numbered from the left, so the name is but-1-ene. But-3-ene numbers from the wrong end; the double bond must have the lowest locant. But-2-ene is CH3CH=CHCH3, with the double bond in the middle of the chain, a positional isomer. Butane has no C=C and has two more hydrogen atoms.
The chain has three carbons, the -ol suffix shows an alcohol and the OH is on C2, so the name is propan-2-ol, a secondary alcohol. Propan-1-ol has the OH on the end carbon (CH3CH2CH2OH). Propan-2-one (propanone) is the ketone CH3COCH3, with C=O, not C-OH. 1-methylethanol misses the longest chain: a methyl on C1 of ethanol extends the chain to three carbons.
Counting the COOH carbon, the chain has three carbons, and the -oic acid suffix shows a carboxylic acid: propanoic acid. Ethanoic acid (CH3COOH) results from not counting the COOH carbon. Propanal is the aldehyde CH3CH2CHO, which has no OH on the carbonyl carbon. Propanone is the ketone CH3COCH3.
The longest chain is five carbons (pentane), with methyl groups on adjacent carbons. Numbering from the right puts them on C2 and C3; from the left they would be on C3 and C4, so 2,3 is the lowest set and the name is 2,3-dimethylpentane. 3,4-dimethylpentane numbers from the wrong end. 2-ethyl-3-methylbutane misses the longest chain, because an ethyl branch extends the main chain to five carbons. 2,3-methylpentane leaves out the di needed for two identical groups.
The acid part, CH3CO-, has two carbons including the C=O carbon, giving ethanoate; the alkyl group on the other oxygen is methyl. So the name is methyl ethanoate (made from ethanoic acid and methanol). Ethyl methanoate, HCOOCH2CH3, reverses the two parts; it is an isomer, not the same compound. Methyl methanoate, HCOOCH3, has one carbon too few. Propanoic acid, CH3CH2COOH, is a functional group isomer with the same molecular formula, C3H6O2, but it has a COOH group, not an ester link.
CH3CH2CN has three carbons including the nitrile carbon, so propanenitrile is correct. CH3CH2CH2CHO is an aldehyde (CHO at the chain end), so it is butanal; butanone is the ketone CH3COCH2CH3. In CH3CHClCH3 the Cl is on the middle carbon, so it is 2-chloropropane; 1-chloropropane is CH3CH2CH2Cl. CH3CH2NH2 has a two-carbon chain, so it is ethylamine (ethanamine); methylamine is CH3NH2.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.