VJC 2024 Alkanes Tutorial

1 Victoria Junior College 2024 JC1 H2 Organic Chemistry Tutorial: Alkanes Summary of Reactions Complete the following table. Starting compound Reaction type Reagents & Conditions Products formed (CH3)2C=CH2 Reduction OR (CH3)2CHCH3 CH4 CCl4 + HCl CHCH3 CH3 CH3 Limited Cl2, UV light (OR high temperature OR heat) CHCH3 CH3 CH2Cl CClCH3 CH3 CH3 + HCl Introduction 1 Write down the displayed formula and skeletal formula for each of the following. (a) 2,2–dimethylbutane (b) 3–ethyl–2,4–dimethylpentane 2 Name the following compounds. (a) CH3(CH2)2CH(CH3)CH(CH3)2 (b) CH3(CH2)2CH(CH3)CH(C2H5)CH(CH3)(C2H5) Reaction mechanism 3 Chloroalkanes and bromoalkanes can be made by the reaction of the corresponding halogen with alkanes, for example: C2H6 + Cl2 → C2H5Cl + HCl (a) State the conditions needed for this reaction. (b) Name and describe the mechanism of this reaction. (c) Why is this reaction described as given in (b)? (d) Suggest why it is not possible to make iodoalkanes by this method. [N10/III/1(c) & (e)]

2 4 Propane undergoes free–radical substitution when mixed with chlorine and exposed to ultra–violet light. Which compounds are possible products from this reaction? 1 CH3CH2CH2Cl 2 CH2ClCH2CH2Cl 3 CH3CH2CH2CH2CH2CH3 4 CH3CH2CH2CH2CH3 A 1, 2 and 3 B 1, 3 and 4 C 1 and 2 only D 2 and 3 only [N19/I/18] 5 Thiocyanogen, (SCN) 2 is a symmetrical pseudohalogen which shows similar chemical reactivity to halogens. When pentane is mixed with thiocyanogen in the presence of UV light, it reacts via the free radical mechanism and compound A was isolated. CH3CH(CH2)2CH3 | S–CΞN Compound A (a) (i) Identify the radical formed in the initiation step for the formation of compound A. (ii) Write an equation to show how this radical is formed from (SCN) 2. You are to draw the full structural formula of (SCN)2 and use ar rows to indicate the movement of electrons so that it is clear which bonds are broken. (b) (i) Propose the 2 steps for the propagation stage of the reaction mechanism in the formation of compound A from pentane. (ii) Draw the two isomers of compound A which show different behaviours towards plane–polarised light. [Modified 2014 VJC Promo P2S2] Substitution at primary, secondary and tertiary carbon atoms 6 When an alkane F, with the formula C 6H14, reacted with bromine under ultraviolet light, it produced only two isomeric monobromo compounds G and H, with the formula C6H13Br. Compound H was chiral. (a) Suggest the structures of F, G and H, explaining your reasoning. (b) Hence, state the expected ratio of the two isomeric monobromo compounds G and H formed based on the probability of substitution o