JPJC 2026 Alkene Assignment Answer

2026 JPJC J1 H2 Chemistry (9476) 1 [Turn Over JURONG PIONEER JUNIOR COLLEGE 2026 JC1 H2 Chemistry (9476) Topical Assignment Topic 10: Alkenes Name : __________________________________________ 10 Class : 26S ___ Date : ____________ Duration : 15 minutes 1 Cyclohexene, C6H10, is one of the important precursors to produce hexanedioic acid, which is widely used to manufacture nylon. Some reactions of cyclohexene are shown in Figure 1. Fig. 1 (a) (i) State the reagents and conditions for reactions 1 to 4. reaction 1: …………………………………………………………………………… reaction 2: …………………………………………………………………………… reaction 3: …………………………………………………………………………… reaction 4: …………………………………………………………………………… [4] concentrated H3PO4, heat (or Al2O3, high temperature) [1] KMnO4(aq) in H2S04(aq), heat [1] Br2 in CCl4 (or Br2 in inert organic solvent), absence of light (or in the dark) [1] OH reaction 4 steam (or H2O(g)), H3PO4, high temperature, high pressure [1] reaction 5 Extension 1: State the type of reaction for reactions 1 to 5. 1: Elimination 2: Oxidation 3: Electrophilic addition 4: Electrophilic addition 5: (mild) oxidation

2026 JPJC J1 H2 Chemistry (9476) 2 (ii) Draw the displayed formula for compound B. [1] (b) But-1-ene is also a common monomer that is used to produce polyalkenes. (i) Predict the major product, P, when but-1-ene is reacted with HBr(g) in the dark. State and draw the mechanism for this reaction for the formation of P. Show any relevant lone pairs, dipoles and charges, and indicate the movement of electron pairs with curly arrows. Major product, P: Mechanism: Electrophilic addition (✓1) (✓1): name of reaction (✓2): + on H and − on Br of H–Br bond (✓3): full arrow from  bond of C=C to H+ of H–Br bond (✓4): full arrow from  bond of H–Br bond to Br− of H–Br bond (✓5): more stable carbocation and balanced equation for slow step (✓6): full arrow from lone pair on Br– to C+ of carbocation and balanced eqn for fast step. (*✓7): indicate “slow” and “fast” steps. 7✓: [2], 3-6✓: [1] [3] [1] (✓2) (✓3) (✓4) (✓5) (✓6) : (*✓7) (*✓7) Must show all the bonds including O—H bonds. [1] Br CH3CHCH2CH3 Br OR OR

2026 JPJC J1 H2 Chemistry (9476) 3 [Turn Over Extension 2: Use your mechanism to explain why P is the major product. 2o carbocation to form P 1o carbocation to form the minor product The secondary (2o) carbocation intermediate to form P is more stable as it has more electron–donating alkyl group attached to C+ such that its positive charge is more dispersed than the primary (1o) carbocation.  the 2o carbocation intermediate is formed more readily and hence P is the major product. (ii) Suggest a simple laboratory test to distinguish between cyclohexene and but-1-ene. State your observations for the test. Test: ……………………………………………………………………………………... ……………………………………………………………………………………………. Observations: …………………………………………………………………………… ……………………………………………………………………………………………. …………………………………………………………………………………………….. [2] Extension 3: Write equations for the reactions that have occurred in the test you used, if any. [Total: 10] To each test sample, add KMnO4(aq) and H2SO4(aq), then heat. Pass any gas evolved through limewater. [1] Both compounds decolourise purple KMnO4. For but-1-ene, effervescence (or gas bubbles) of CO2 is observed and the gas evolved forms a white ppt. with limewater. For cyclohexene, no effervescence of CO2 is formed. [1] both observations