2024 VJC Alkenes Tutorial

1 Victoria Junior College 2024 JC1 H2 Organic Chemistry Tutorial: Alkenes Summary of Reactions Complete the following table. 1 Preparation of Alkenes Starting compound Reaction type Reagents & Conditions Products formed CH3CH2CH2OH Elimination Excess conc. H2SO4, heat OR Al2O3, heat CH3CH(Br)CH2CH3 2 Reactions of Alkenes Starting compound Reaction type Reagents & Conditions Carbon-containing product(s) CH3CH2CH=CH2 HBr(g) CH3CH2CH(Br)CH2Br Br2(aq) CH3CH2CH(OH)CH3 CH3CH2CH2CH3 Oxidation cold KMnO4 in NaOH(aq) KMnO4 in H2SO4(aq), heat Note: If no heat is written for a reaction, it means that the reaction can take place at room temperature.

2 Introduction 1 Write down the skeletal formula for each of the following. (a) 4–bromopent–1–ene (b) cis–2,2–dimethylhex–3–ene 2 Give the IUPAC name for each of the following. (a) (CH3)2C=CHCH3 (b) Reaction mechanism 3 (a) Name the type of reaction and describe the mechanism for the reaction between but–1–ene and hydrogen bromide to form 2 –bromobutane. Show all charges and relevant lone pairs and show the movement of electron pairs using curly arrows. (b) State the type of hybridisation in the alkene carbon atom of but –1–ene and the reactive carbon atom in the intermediate formed in the mechanism. (c) By referring to the shape of the reactive carbon atom in the intermediate formed in the mechanism, e xplain why compound formed from the reaction between but–1–ene and hydrogen bromide has no effect on plane-polarised light. (d)(i) Write an equation, giving the structural formula of the major organic product, for the reaction between but–1–ene and aqueous bromine under room temperature. (ii) [EXTENSION] Describe the mechanism written in (d)(i). Show all charges and relevant lone pairs and show the movement of electron pairs using curly arrows. Electrophilic addition of alkenes 4 Hydrogen iodide undergoes an addition reaction with propene forming 2 –iodopropane. When propene is bubbled through iodine monochloride, ICl, dissolved in a suitable solvent, a similar reaction occurs. Which product will be present in the greatest yield? A B C D CH3CHCH2Cl Cl CH3CHCH2I I CH3CHCH2I Cl CH3CHCH2Cl I [N13/I/21] Oxidative cleavage of alkenes 5 The following compound is used as an alarm pheromone by some aphids. Which product is obtained from the reaction of this pheromone with excess hot concentrated acidic KMnO4? A CH3COCH2CHO B CH3COCH2CH2CO2H C HCHO D HO2CCH2COC(CH3)=CH2

3 6 An alkene, X, has the molecular formula C5H10. On oxidation with hot acidified potassium manganate(VII) solution, X gives rise to CH3(CH2)2CO2H as the only organic compound. Deduce the structure of X, and using [O] notation, write the equation for the above reaction. 7 An alkane