Which compound has the empirical formula CH2O?
- butane-2,3-diol
- ethanol
- methyl methanoate
- propanoic acid
Show answer and explanation
Answer: C. methyl methanoate
Methyl methanoate is C2H4O2, which simplifies to CH2O.
A Level Chemistry: Organic chemistry intro, questions with answers
Practise 15 real questions on Organic chemistry intro from 2021 to 2026. See the answer and explanation as soon as you answer.
15real questions
15multiple choice
8exam sessions
About Organic chemistry intro in A Level Chemistry
Organic chemistry intro is one of the 18 main topics in our A Level Chemistry (Cambridge (CAIE) 9701) question bank, and about 2% of its real questions come from it. Tayyari Karo has 15 real questions on this topic from 2021 to 2026, from Paper 1; 15 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 8 hard, 6 medium, 1 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
Try 6 real questions
These are real past-paper questions. Think of your answer first, then open the explanation.
Structural isomerism and stereoisomerism should be taken into account. 3-methylcyclobutene (a cyclobutene ring with a methyl substituent on C3) is treated as a mixture of all its stereoisomers with HBr, producing a mixture of isomeric bromomethylcyclobutanes. How many stereoisomers does 3-methylcyclobutene have, and how many isomeric bromomethylcyclobutanes are present in the product mixture?
- 2 stereoisomers; 4 bromomethylcyclobutanes
- 2 stereoisomers; 6 bromomethylcyclobutanes
- 4 stereoisomers; 4 bromomethylcyclobutanes
- 4 stereoisomers; 8 bromomethylcyclobutanes
Show answer and explanation
Answer: B. 2 stereoisomers; 6 bromomethylcyclobutanes
3-methylcyclobutene has one stereocentre (C3) giving 2 stereoisomers (enantiomers); electrophilic addition of HBr across the ring double bond can occur with either regiochemistry and generates new stereocentres, giving 6 isomeric bromomethylcyclobutane products overall.
Which compound has the greatest number of stereoisomers?
- 2-methylhex-2-ene
- 3-methylhex-2-ene
- 4-methylhex-2-ene
- 5-methylhex-2-ene
Show answer and explanation
Answer: C. 4-methylhex-2-ene
4-methylhex-2-ene, CH3–CH=CH–CH(CH3)–CH2–CH3, has E/Z isomerism about the C2=C3 double bond (2 forms) as well as a chiral centre at C4 (2 forms), giving 2×2 = 4 stereoisomers in total — more than the other options, which each have at most simple E/Z isomerism (2 isomers) or none.
An organic molecule W contains 3 carbon atoms. It requires 4.5 molecules of oxygen for complete combustion. What could W be?
- propane
- propanoic acid
- propanone
- propan-1-ol
Show answer and explanation
Answer: D. propan-1-ol
C3H8O + 4.5O2 → 3CO2 + 4H2O balances exactly for propan-1-ol (C3H7OH), needing 4.5 mol O2 per mole of alcohol.
The sweetener aspartame has the structure HOOC–CH2–CH(NH2)–C(=O)–NH–CH(CH2C6H5)–C(=O)–O–CH3 (an aspartic acid unit linked to the methyl ester of phenylalanine). Aspartame is chiral (there are no chiral carbon atoms in the C6H5 ring). How many chiral carbon atoms are present in a molecule of aspartame?
- 1
- 2
- 3
- 4
Show answer and explanation
Answer: B. 2
The two carbons bearing four different groups are the CH(NH2) carbon of the aspartic acid residue and the CH(CH2C6H5) carbon of the phenylalanine residue — 2 chiral centres.
Which pair of reagents react together in a redox reaction?
- CH3CHCH2 + Br2
- CH3CH2CH2OH + concentrated H3PO4
- CH3COCH3 + HCN
- HCO2C2H5 + dilute H2SO4
Show answer and explanation
Answer: A. CH3CHCH2 + Br2
Addition of Br2 across the alkene double bond of propene is a redox (addition) reaction in which bromine is reduced and the alkene carbons are oxidised; the other options are substitution/addition-elimination or hydrolysis reactions without oxidation state change at carbon overall.
Sessions with Organic chemistry intro questions
| Session | Paper 1 |
|---|---|
| May/June 2026 | 3 |
| October/November 2025 | 2 |
| May/June 2024 | 3 |
| October/November 2024 | 2 |
| May/June 2023 | 1 |
| October/November 2023 | 2 |
| October/November 2022 | 1 |
| May/June 2021 | 1 |
Common questions
What does the Organic chemistry intro topic cover on this page?
15 real A Level Chemistry (9701) questions on Organic chemistry intro from 2021 to 2026, from Paper 1. Each one shows the year, session and paper it came from.
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Yes. Every question shows the correct answer and a short explanation the moment you answer.
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Other Chemistry topics
- Group 2 41
- Periodic Table periodicity 38
- Chemical bonding 36
- Hydrocarbons 36
- Carboxylic acids 33
- Atoms/molecules/stoichiometry 30
- Equilibria 30
- Group 17 30
- Carbonyl compounds 30
- Chemical energetics 29
- Reaction kinetics 29
- Halogen compounds 29
- Hydroxy compounds 28
- Atomic structure 26
- Nitrogen and sulfur 25
- Analytical techniques 22
- Electrochemistry 17