Organic Chemistry
7 marks · EasyAnswer all parts about reactions of hydrocarbons with halogens. You may use displayed formulae or structural formulae where needed.
Write a balanced chemical equation for the reaction between ethane and chlorine, naming the type of reaction.
Draw and name the two possible mono-bromo isomers formed when propane reacts with bromine under UV light.
But-2-ene (C4H8) can also react with bromine. Draw the structure of one product formed, and name the type of reaction.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) CH3CH3 + Cl2 → CH3CH2Cl + HCl (substitution) · must show balanced equation, recognises as substitution reaction
(b) 1-bromopropane & 2-bromopropane (drawn) · must show both isomers drawn, correct placement of Br
(c) 1,2-dibromobutane, from addition reaction · must show product structure with Br atoms on adjacent carbons, correct bond arrangement
Common mistakes: writing addition instead of substitution; incorrect number of bromines or position
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Writes correct balanced equation for ethane + chlorine.
B1 (a) · 1 mark · Names the reaction as substitution.
D1 (b) · 1 mark · Draws 1-bromopropane (Br at end carbon).
D1 (b) · 1 mark · Draws 2-bromopropane (Br at middle carbon).
B1 (b) · 1 mark · Gives the correct names for both isomers.
D1 (c) · 1 mark · Draws structure of 1,2-dibromobutane (addition product, Br on C-1 and C-2).
B1 (c) · 1 mark · Names the reaction as addition.
Worked solution
a) Ethane reacts with chlorine (in UV light): CH3CH3 + Cl2 → CH3CH2Cl + HCl. This is a substitution reaction.
b) When propane reacts with bromine, mono-substitution forms two isomers:
1-bromopropane
2-bromopropane
c) But-2-ene (CH3CH=CHCH3) reacts with Br2 by addition across C=C to give 2,3-dibromobutane.
The type of reaction is addition.