Dr. Emanuele Chemistry Tutor - Topic 15: Organic Chemistry

A Level Official Exam Material

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Unit 5: Transition Metals and

Organic Nitrogen Chemistry

Topic 15: Organic Chemistry

For A Level students only

Q1. For each question, select one answer from A to D and put a cross in the box .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

Menthol has a number of medicinal uses.

It can be extracted from the peppermint plant.

The structure of menthol is

How many chiral centres are there in one molecule of menthol?

A 1

B 2

C 3

D 4

(Total for question = 1 mark)

Q2. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

The compound menthol has the structure shown.

Some of the carbon atoms are labelled P, Q, R and S.

(a) What is the number of chiral centres in a molecule of menthol? (1)

A 1

B 2

C 3

D 4

(b) Which of the carbon atoms is responsible for a peak at 72 ppm in the 13C NMR spectrum of menthol? (1)

A P

B Q

C R

D S

They purified the reaction mixture and carried out a series of qualitative tests on the organic product.

The findings of each group in the class are shown in the table.

A One

B Two

C Three

D Four

(Total for question = 3 marks)

Q3. When mixed in equimolar quantities, which pair of molecules will not rotate the plane of plane-polarised light?

Q4. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

How many optical isomers does this molecule have?

Q5. For each question, select one answer from A to D and put a cross in the box .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

When a single enantiomer of 2-iodobutane reacts with sodium hydroxide, the product is a mixture of enantiomers.

This is because

A the reaction is a nucleophilic substitution

B the reaction proceeds via a negatively charged transition state

C the reaction proceeds via a carbocation intermediate

D the reaction rate depends on the concentration of 2-iodobutane

(Total for question = 1 mark)

Q6. For each question, select one answer from A to D and put a cross in the box .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

Which of these reactions does not result in the formation of a racemic mixture?

A but-2-ene with HCl

B but-1-ene with HCl

C propanal with HCN

D propanone with HCN

(Total for question = 1 mark)

Q7. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

Which of these structures is not identical to the others?

Q8. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross . Citronellol is found in rose and geranium oils.

Q9. Which of these molecules can rotate the plane of plane-polarised light?

A H2NCH2COOH

B HOCH2CH2COOH

C ClCH2C(CH3)(Cl)COOH

D H2NC(CH3)2COOH

(Total for question = 1 mark)

Q10. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

A sample of a bromoalkane, RBr, containing a single optical isomer reacts with hydroxide ions in an SN1 mechanism.

RBr + OH− → ROH + Br−

The alcohol formed is a racemic mixture.

From this information, it can be deduced that RBr is most likely to be

A primary only

B secondary only

C tertiary only

D primary, secondary or tertiary

(Total for question = 1 mark)

Q11. * Compare and contrast the reactions of propanal and propanone with one oxidising agent, one reducing agent and 2,4-dinitrophenylhydrazine.

In your answer include any relevant observations for the reactions you discuss and equations for any reactions classified as oxidation, using [O] for the oxygen from the oxidising agent.

(Total for question = 6 marks)

Q11a. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

The following methods can be used to distinguish between pairs of organic compounds with no further tests.

A warm each compound with Fehling's or Benedict's solution

B warm each compound with acidified potassium dichromate(VI) solution

C add 2,4-dinitrophenylhydrazine (Brady's reagent) to each compound

D add a few drops of each compound, drop by drop, to water

(a) Which test would distinguish between 2-methylpropan-2-ol, (CH3)3COH, and butanone, CH3CH2COCH3? (1)

(b) Which test would distinguish between 2-methylpropan-2-ol, (CH3)3COH, and butan-1-ol, CH3CH2CH2CH2OH? (1)

(Total for question = 3 marks)

Q12. The compound lactic acid can be synthesised from ethanal in two steps

(a) (i) Give the mechanism for Step 1.

Include curly arrows, and any relevant lone pairs and dipoles. (4)

(ii) A student predicted that the product of Step 1 would rotate the plane of plane-polarised light.

Comment on this prediction. (3)

(iii) Complete the table that summarises information about Step 2.

State symbols are not required for the equation. (4)

(b) Sodium hydrogencarbonate, NaHCO3 , has been used by some athletes to help prevent lactic acid causing muscle pain during exercise.

Write an equation for the reaction between sodium hydrogencarbonate and lactic acid. (1)

Two of the equilibria involved in this process are shown.

(i) Use the equilibria to explain how the buffer keeps the pH of blood nearly constant when a small increase in the concentration of hydrogen ions occurs. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(ii) The pH of a blood sample was found to be 7.41.

Calculate the ratio of the concentration of in the blood sample.

Q13. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

A compound X, with molecular formula C5H10O , gave an orange precipitate with 2,4- dinitrophenylhydrazine.

X gave a silver mirror with Tollens' reagent.

Which of these could not be X?

Q14. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

Ethanal and propane have the same molar mass but ethanal has a much higher boiling temperature.

Ethanal is fully miscible in water but propane is almost insoluble.

Which intermolecular forces of ethanal are mainly responsible for the differences in these properties?

Q15. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

When propanone reacts with iodine in the presence of sodium hydroxide, the precipitate formed has the formula

A CH3I

B CHI3

C CH3COCH2I

D CH3COCI3

(Total for question = 1 mark)

Q16. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

An unknown aldehyde may be identified by measuring the melting temperature of the purified precipitate formed in its reaction with:

A 2,4-dinitrophenylhydrazine

B Fehling's solution

C potassium dichromate and sulfuric acid

D Tollens' reagent

(Total for question = 1 mark)

Q17. Propanal reacts very slowly with HCN at 298 K.

To increase the rate of reaction potassium cyanide, KCN, is added.

(a)(i) Complete the mechanism for this reaction by adding curly arrows, and relevant lone pairs and dipoles to Step 1 and Step 2.

(ii) Explain why the reaction between propanal and HCN in the absence of KCN is very slow, referring to the value of Ka. No calculation is required. [For HCN, Ka = 4.9 × 10–10 mol dm–3 ] (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(iii) KCN is a homogeneous catalyst in this reaction. Justify this description by referring to the mechanism. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(b) The organic products of this reaction are enantiomers.

Draw the three-dimensional structures of these enantiomers. (2)

(Total for question = 10 marks)

Q18. Which compound gives a pale yellow precipitate on warming with a solution of iodine and sodium hydroxide? (1)

A CH3OH

B CH3CH2CH2CHO

C CH3CH2COCH3

D CH3CH2COCH2CH3

(Total for question = 1 mark)

Q19. For each question, select one answer from A to D and put a cross in the box . If you change your mind about an answer, put a line through the box and then mark your new answer with a cross . How many structural isomers with the molecular formula C5H10O react with Tollens' reagent? A 2 B 3 C 4 D 5 (Total for question = 1 mark)

Q20. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

Butanoic acid may be prepared by the acid hydrolysis of

A butyl ethanoate

B 1-chlorobutane

C ethyl butanoate

D propanenitrile

(Total for question = 1 mark)

Q21. This question is about compounds with the molecular formula C6H12O2.

(a) Hexanoic acid, C5H11COOH, is a weak acid.

(i) Write the equation for the acid dissociation constant, Ka, of hexanoic acid. (1)

(ii) Calculate the pH of a 0.100 mol dm–3 solution of hexanoic acid. [pKa of hexanoic acid = 4.88] (4)

(iii) The solubility of hexanoic acid in water is 1.08 g per 100 g of water.

The isomer of hexanoic acid, butyl ethanoate, CH3CO2C4H9, has a solubility of 0.68 g per 100 g of water.

Explain the differences in these data in terms of the hydrogen bonding between hexanoic acid and water, and between butyl ethanoate and water. (3)

............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(b)(i) Compound A is thought to be another isomer of hexanoic acid. 10 g of compound A is found to contain 6.21 g of carbon and 1.03 g of hydrogen, with the remainder being oxygen.

Use the data to calculate the empirical formula of compound A.

You must show all your working. (3)

Q22. Which compound has the highest boiling temperature? (1)

A butanal

B butan-1-ol

C butanone

D butanoic acid

(Total for question = 1 mark)

Q23. Answer the question with a cross in the box you think is correct .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

An organic compound that reacts with both lithium tetrahydridoaluminate(III) (lithium aluminium hydride) and magnesium could be

A an aldehyde

B a carboxylic acid

C a ketone

D a tertiary alcohol

(Total for question = 1 mark)

Q24. Which reaction does not produce a carboxylic acid? (1)

A hydrolysis of an acyl chloride with cold water

B hydrolysis of an ester by refluxing with dilute hydrochloric acid

C hydrolysis of a nitrile by refluxing with aqueous potassium hydroxide

D oxidation of a primary alcohol by refluxing with excess acidified potassium dichromate

(Total for question = 1 mark)

Q25. Which of these reacts directly with ethanoic acid to form ethanoyl chloride?

A chlorine

B chloroethane

C hydrogen chloride

D phosphorus(V) chloride

(Total for question = 1 mark)

Q26. Carboxylic acids and acyl chlorides both react with alcohols to produce esters.

Acyl chlorides are often preferred to carboxylic acids for this reaction because the yield of the ester is usually higher.

Which of the following statements is the best explanation for the higher yield? (1)

A acyl chlorides react to remove any water produced

B the reaction is not reversible

C the reaction is less exothermic

D the reaction has a higher atom economy

(Total for question = 1 mark)

Q27. For each question, select one answer from A to D and put a cross in the box .

If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .

Which of these compounds is a product of the hydrolysis of CH3COOC3H7 by refluxing with aqueous sodium hydroxide? A CH3OH

B C3H7OH

C C3H7COOH

D C3H7COO–Na+

(Total for question = 1 mark)

Q28. Compound X is used by mammals as an alternative energy source to sugars.

X is a compound of carbon, hydrogen and oxygen only.

(a) Complete combustion of a 2.50 g sample of X in dry oxygen produced 4.31 g of carbon dioxide and 1.32 g of water as the only products.

(i) Give a reason why the oxygen used must be dry. (1) ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(ii) Show that the empirical formula of X is C4H6O3.

You must show your working. (5)

(b) Compound X gave an orange precipitate with Brady's reagent (2,4-dinitrophenylhydrazine) but no reaction with Tollens' reagent.

When X was added to a solution of sodium hydrogencarbonate, effervescence occurred and the gas evolved turned limewater cloudy.

The carbon-13 NMR spectrum of X had only four peaks.

(i) Deduce the two possible structures of X, showing how this information supports your answer. (6)

(ii) Give a chemical test which would allow you to distinguish between the two compounds you have given in (b)(i).

Include the reagents required and the result for each of the compounds. (3)

Explain how the number of peaks in the 1H NMR spectrum, together with their relative heights, their chemical shifts and their splitting patterns, may be used to confirm the structure of X. Use the chemical shifts given in your Data Booklet. (5)

(Total for question = 20 marks)

Q29. One of the compounds responsible for the characteristic smell of bananas is 3-methylbutyl ethanoate. The structural formula of this compound is: CH3COOCH2CH2CH(CH3)2 (a) Draw the skeletal formula for 3-methylbutyl ethanoate. (1) (b) The infrared spectrum of a sample of 3-methylbutyl ethanoate is shown below.

(i) Use this spectrum to identify one peak resulting from a bond in the ester group of 3-methylbutyl ethanoate.

Include the relevant bond and its wavenumber range. (1) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(ii) 3-methylbutyl ethanoate was synthesised by reacting a suitable carboxylic acid with an alcohol. Show that its infrared spectrum confirms there is no alcohol remaining in the sample. (1) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

*(c) The high resolution proton nuclear magnetic resonance (NMR) spectrum of a different ester, ethyl ethanoate, CH3COOCH2CH3, is shown.

The numbers over each peak represent their approximate relative areas.

Show that the structure of ethyl ethanoate is consistent with this NMR spectrum, using all the data in the spectrum. (6) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(d) Ethyl ethanoate has three isomers which are also esters.

(i) Draw the structures of these three isomers. (2)

(ii) Explain to what extent it is possible to distinguish between the three isomers using carbon-13 NMR spectroscopy. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(Total for question = 13 marks)

If you need the markscheme, including the examiners' reports for each question, and more exam and teaching materials on this topic, contact me through the contact page

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