2026 NYJC Alkenes Exercise Questions

OC03 Alkenes H2 Chemistry 9476 Nanyang Junior College Page 1 JC2 / 2026 3 Alkenes Exercise 1 Draw the skeletal structures to show the isomers for alkenes of molecular formulae C5H10. Identify structures that can display cis-trans isomerism. 2 When 0.1 mol of a hydrocarbon Y reacts with hot acidified KMnO4, 4.80 dm3 of CO2 is produced under room temperature and pressure. What is the possible structural formula of Y? A CH3CH2CH2CH3. B CH3CH2CH=CH2 C CH2=CHCH2CH2CH=CHCH3 D CH2=CHCH2CH2CH2CH=CH2 3 The bond lengths in propyne differ from those which might be expected. The carbon-carbon bond length in ethane is 0.154 nm and in ethyne is 0.120 nm. The single C2–C3 bond in propyne, however, is shorter than the single bond in ethane: it is 0.146 nm. C H C CH3 1 2 3 0.146 nm propyne What helps to explain this C2–C3 bond length? A It has a partial sp2–sp2 character. B It is an sp–sp3 overlap. C The sp3–sp3 bonding is pulled shorter by a p–p (-bond) overlap. D The electrons in the C3 carbon atom are attracted the -bonds towards between C1 and C2.

OC03 Alkenes H2 Chemistry 9476 Nanyang Junior College Page 2 JC2 / 2026 4 Epoxy resins are polymers which are used as adhesives. One monomer used in their manufacture has the following structure. This is manufactured from propene in three stages: Stage I: Stage II: Stage III: (a) (i) What type of reaction has taken place between propene and chlorine gas in Stage I? (ii) Suggest what conditions are necessary for this reaction. (iii) Write out the mechanism for this reaction. (b) (i) What type of reaction has taken place between 3-chloroprop-1-ene and Br2(aq) in stage II? (ii) Outline the mechanism for this reaction.

OC03 Alkenes H2 Chemistry 9476 Nanyang Junior College Page 3 JC2 / 2026 5 Which of the following is the major product formed when compound X reacts with HBr? compound X A B C D 6 -selinene can be isolated from plant material. -selinene When -selinene reacts completely with HBr, the product mixture contains different compounds, all with the same molecular formula. Which row identifies the molecular formula of the products and the number of these products which are tertiary bromoalkanes? molecular formula of the products number of products which are tertiary bromoalkanes A C15H24Br2 2 B C15H24Br2 3 C C15H26Br2 2 D C15H26Br2 3

OC03 Alkenes H2 Chemistry 9476 Nanyang Junior College Page 4 JC2 / 2026 7 C4H8 can exist in 4 non-cyclic isomers forms, W, X, Y and Z. W has the structure as shown: W reacts with chlorine under two different conditions. Reaction I: In the absence of light, W reacts with Cl 2 dissolved in CCl 4 to give an equimolar mixture of two isomers A and B. Reaction II: W reacts with Cl2 gas under ultraviolet light to give CH2=CH(CH2CH2Cl). However, the presence of trace amount of nitrogen monoxide may decrease the rate of reaction. (a) Draw the isomeric structures of X, Y and Z and identify the types of isomerism present. (b) Draw the displayed formulae of isomers A and B in reaction I. (c) Explain why the following step rarely occurs in reaction II. CH2=CH(CH2CH3) + Cl • → CH2=CH(CH2CH2Cl) + H• (d) Suggest why the presence of nitrogen monoxide will slow down reaction II. 8 Give the structural formula of the product(s) formed when compound X reacts with each of the following reagents. (a) Cold acidified KMnO4 (b) Hot alkaline KMnO4 (c) HBr at room temperature

OC03 Alkenes H2 Chemistry 9476 Nanyang Junior College Page 5 JC2 / 2026 9 Which of the following is not a product formed when compound Z reacts with hot acidified KMnO4? A B C D 10(a) On complete combustion, 0.00754 mol of a hydrocarbon E gave 2.654g of CO 2 and 0.543 g of H2O. (i) Determine the molecular formula of E. (ii) Construct an equation for the complete combustion of E. (b) E burns with a smoky flame. 1 mol of E reacts with 1 mol of bromine molecules. (Hint: a benzene ring exist) (i) Draw a displayed formula of E. (ii) Draw the displayed formula of the product formed between E and bromine. (c) (i) What organic product would you expect if E is heated under reflux wit h concentrated alkaline potassium manganate(VII)? (ii) Suggest what colour change might be observed.

OC03 Alkenes H2 Chemistry 9476 Nanyang Junior College Page 6 JC2 / 2026 11 The oxo reaction is an important industrial process in which an alkene combines directly with carbon monoxide and hydrogen under suitable conditions. The reaction with ethene is shown below: CH2=CH2 + CO + H2 ⎯⎯⎯⎯→ CH3CH2CHO Which of the following structural formulae correctly represents the product of the oxo reaction starting with but-2-ene? A CH3CH2CH(CH3)CHO B CH3CH2CH2CH2CHO C CH3CH2COCH2CH3 D CH3COCH2CH2CH3 catalyst High T, p