Organic SynthesisEdexcel International A Level Chemistry: Topic test

20 questions, 54 marks

Edexcel International A Level Chemistry

Organic Synthesis topic test

Total 54 marks

Name

Class

Date

1
Compound P contains only carbon, hydrogen and oxygen. Complete combustion of 0.510 g of P gives 1.100 g of carbon dioxide and 0.450 g of water. The molecular ion peak in the mass spectrum of P is at m/z 102. Ar: C = 12.0, H = 1.0, O = 16.0.
(a)
What is the empirical formula of P?
[1 mark]
AC₂H₅O
BC₅H₁₀O₂
CC₅H₁₂O
DC₄H₁₀O
(b)
Which feature of the infrared spectrum would show that P is a carboxylic acid rather than an ester?
[1 mark]
AA strong absorption at about 1740 cm⁻¹
BA C–H absorption between 2850 and 3100 cm⁻¹
CA C–O absorption between 1000 and 1300 cm⁻¹
DA very broad absorption between 2500 and 3300 cm⁻¹
(c)
The infrared spectrum of P has a strong absorption at 1740 cm⁻¹ and no broad absorption above 2500 cm⁻¹. The proton NMR spectrum has four signals: a triplet of 3H at δ 1.1, a triplet of 3H at δ 1.2, a quartet of 2H at δ 2.3 and a quartet of 2H at δ 4.1. Deduce the structure of P, giving your reasoning.
[2 marks]
Total for question 1: 4 marks
2
A chemist reacts the Grignard reagent (CH₃)₂CHMgBr with methanal, HCHO, in dry ethoxyethane and then adds dilute acid.
(a)
What is the organic product of this reaction sequence?
[1 mark]
A2-Methylpropan-1-ol
B2-Methylpropan-2-ol
CButan-2-ol
D3-Methylbutan-2-ol
(b)
Why must the apparatus and the ethoxyethane be completely dry?
[1 mark]
AMagnesium will not dissolve if water is present
BWater would act as a catalyst for a side reaction
CWater would protonate the Grignard reagent, converting it to propane
DWater would oxidise the alcohol product to a carboxylic acid
(c)
Write an equation for the formation of the Grignard reagent, giving the conditions, and explain why the carbon atom bonded to magnesium acts as a nucleophile.
[2 marks]
Total for question 2: 4 marks
3
A student prepares 2-chloro-2-methylpropane, (CH₃)₃CCl (Mr = 92.5), by shaking 10.0 cm³ of 2-methylpropan-2-ol, (CH₃)₃COH (density 0.789 g cm⁻³, Mr = 74.0), with an excess of concentrated hydrochloric acid in a separating funnel. The crude product is washed with sodium hydrogencarbonate solution, dried and distilled, collecting the fraction that boils between 49 °C and 52 °C. The student obtains 5.62 g of pure product.
(a)
Calculate the percentage yield of 2-chloro-2-methylpropane.
[3 marks]
(b)
Explain the purpose of each of the following steps. (i) Washing the crude product with sodium hydrogencarbonate solution, and what would be seen. [2]
(ii) Adding anhydrous calcium chloride to the washed product. [1]
(iii) Collecting only the fraction that boils between 49 °C and 52 °C. [1]
[4 marks]
Total for question 3: 7 marks
4
Butan-2-ol, CH₃CH(OH)CH₂CH₃, is to be synthesised using ethanol as the only organic starting material. Hazard data: ethoxyethane is extremely flammable (flash point –45 °C); acidified potassium dichromate(VI) is toxic and a suspected carcinogen; bromoethane is harmful and flammable (boiling temperature 38 °C).
(a)
Plan a four-step synthesis of butan-2-ol from ethanol. For each step give the reagents and conditions and the organic product.
[6 marks]
(b)
Using the hazard data, describe the practical procedure for the oxidation of ethanol to ethanal and identify the control measures needed in the synthesis.
[6 marks]
Total for question 4: 12 marks
5
Compound Q has molecular formula C₅H₁₀O. It forms an orange precipitate with 2,4-dinitrophenylhydrazine but gives no silver mirror with Tollens' reagent. Its proton NMR spectrum has only two signals: a triplet integrating for 6H and a quartet integrating for 4H.
(a)
How many peaks are there in the carbon-13 NMR spectrum of compound Q?
[1 mark]
A2
B5
C3
D4
(b)
Which fragment ion gives a peak at m/z 57 in the mass spectrum of compound Q?
[1 mark]
ACH₃CH₂CO⁺
BCH₃CO⁺
CCH₃CH₂⁺
D(CH₃CH₂)₂CH⁺
(c)
Explain how the proton NMR spectrum is consistent with Q being pentan-3-one.
[2 marks]
Total for question 5: 4 marks
6
A student purifies crude benzoic acid, which contains a small amount of an insoluble impurity and a small amount of a soluble impurity, by recrystallisation from hot water.
(a)
Why is the minimum volume of hot water used to dissolve the crude benzoic acid?
[1 mark]
ATo prevent the benzoic acid decomposing
BSo that the soluble impurity crystallises first
CSo that the insoluble impurity dissolves
DSo that the solution is saturated and as much benzoic acid as possible crystallises on cooling
(b)
How does the melting temperature of the impure benzoic acid compare with that of the pure acid?
[1 mark]
AHigher and sharp
BLower and over a range
CThe same but over a range
DHigher and over a range
(c)
Explain why the hot solution is filtered while hot, and why the crystals are finally washed with a small amount of ice-cold water.
[2 marks]
Total for question 6: 4 marks
7
A chemist plans a two-step synthesis of propanenitrile, CH₃CH₂CN (Mr = 55.0), from ethanol, CH₃CH₂OH (Mr = 46.0). Step 1 converts ethanol into bromoethane with a percentage yield of 78.0%. Step 2 converts bromoethane into propanenitrile by heating under reflux with ethanolic potassium cyanide, with a percentage yield of 65.0%.
(a)
Calculate the maximum mass of propanenitrile that could be made from 20.0 g of ethanol if both steps had a yield of 100%.
[3 marks]
(b)
(i) Calculate the overall percentage yield of the two-step synthesis. [2]
(ii) Calculate the mass of propanenitrile actually obtained from 20.0 g of ethanol. [1]
(iii) Explain why the overall yield is lower than the yield of either step. [1]
[4 marks]
Total for question 7: 7 marks
8
Compound R has molecular formula C₄H₈O₂. Its infrared spectrum has a very broad absorption between 2500 cm⁻¹ and 3300 cm⁻¹ and a strong absorption at 1710 cm⁻¹. Its proton NMR spectrum has three signals: a doublet integrating for 6H, a septet integrating for 1H and a singlet integrating for 1H at δ 11.5.
(a)
Deduce the structure of compound R, explaining how each piece of evidence supports your answer.
[6 marks]
(b)
Compound R can be synthesised from 2-bromopropane, (CH₃)₂CHBr, using a Grignard reagent. Describe the synthesis, giving reagents, conditions and equations, and explain why the carbon chain length changes.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).