Edexcel IAL Chemistry A2 Topic 15 Carbonyls, Carboxylic Acids and Chirality

Pearson Edexcel IAL Chemistry syllabusChemistry YCH11First assessment 2019

Move between structure and evidence: identify chiral centres, choose carbonyl tests and reagents, and use mechanisms or observations to justify organic products.

Exam points

Identify chiral centres, enantiomers and optical activity from displayed or skeletal structures.
Use Tollens, Fehling, 2,4-DNPH, iodoform and dichromate observations for carbonyls.
Apply organic mechanisms and reagent conditions to predict alcohol, cyanohydrin or acid products.

[Maximum number: 10]

This question is about the identification of three organic compounds, X, Y and Z.
A molecule of each compound has only one type of functional group. Each compound contains six carbon atoms and two oxygen atoms.

In the mass spectrum of X, the molecular ion peak is at m / z=114.

(a)

Three chemical tests are carried out on X.

Test 1 When Brady's reagent (2,4-dinitrophenylhydrazine solution) is added to X, an orange precipitate is observed.

Test 2 When X is heated with an acidified solution of potassium dichromate(VI), no change is observed.

Test 3 When X is added to an alkaline solution of iodine, the formation of a pale yellow precipitate is observed.

Explain what can be deduced about the functional group present in X, by considering the results of each of these tests.
(b) Three chemical tests are carried out on X.

[ 3 ]

(b)

The high resolution proton NMR spectrum of X contains only two singlets with relative peak areas of 3: 2.

Draw the structure of X, identifying the two proton environments.

[ 2 ]

(c)

The molecular formula of Y is $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{2}$ .

[ 5 ]

(i)

When aqueous sodium carbonate is added to Y, effervescence is observed. Identify, by name or formula, the functional group present in Y.

[ 1 ]

(ii)

The ${ }^{13} \mathrm{C}$ NMR spectrum of Y contains four peaks.

Give two possible structures for Y.

[ 2 ]

(iii)

Explain how the low resolution proton NMR spectrum of Y would confirm which of your structures in (d)(ii) is correct. Chemical shifts are not required.

[ 2 ]

[Maximum number: 1]

Propanone reacts with iodine in both acidic and alkaline conditions.

The products of the reactions under the stated conditions include
□ A
□ B
□ C
□ D

[Maximum number: 1]

Methylbenzene reacts with a mixture of concentrated nitric acid and concentrated sulfuric acid to form 2,4,6-trinitromethylbenzene.

What is the number of peaks in the ${ }^{13} \mathrm{C}$ NMR spectrum of methylbenzene?

seven

six

five

four

[Maximum number: 8]

Propanal reacts very slowly with HCN at 298 K . To increase the rate of reaction potassium cyanide, KCN, is added.

(a)

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

Step 1

{ }^{-} \mathrm{C} \equiv \mathrm{~N}

Step 2

⟶ products
intermediate

[ 4 ]

(b)

KCN is a homogeneous catalyst in this reaction.

Justify this description by referring to the mechanism.
(2)

[ 2 ]

(c)

The organic products of this reaction are enantiomers.

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

[ 2 ]

[Maximum number: 5]

This question is about compounds with the molecular formula $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{2}$ .

(a)

Hexanoic acid, $\mathrm{C}_{5} \mathrm{H}_{11} \mathrm{COOH}$ , is a weak acid.

[ 3 ]

(i)

The solubility of hexanoic acid in water is 1.08 g per 100 g of water. The isomer of hexanoic acid, butyl ethanoate, $\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{C}_{4} \mathrm{H}_{9}$ , 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)

[ 3 ]

(b)

Compound B, another isomer with the molecular formula $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{2}$ , contains a ring of six carbon atoms.

The carbon-13 NMR spectrum has only two peaks, one of which is at 69 ppm.
Draw the structure of compound B.
(2)

[ 2 ]

[Maximum number: 6]

Esters are used in flavourings and perfumes.
They can be made by reactions involving alcohols.

(a)

An ester which smells of raspberries can be formed by either of two different reactions.

Reaction 1
catalyst

\mathrm{HCOOH}+\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{OH} \rightleftharpoons \mathrm{HCOOCH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}+\mathrm{H}_{2} \mathrm{O}

Reaction 2

\mathrm{HCOCl}+\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{OH} \rightarrow \mathrm{HCOOCH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}+\mathrm{HCl}

[ 6 ]

(i)

Name the carboxylic acid, alcohol and catalyst used in Reaction 1.

HCOOH catalyst
$\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{OH}$

[ 2 ]

(ii)

Explain one advantage and one disadvantage of using Reaction 2 rather than Reaction 1.

SECTION C

Answer ALL the questions. Write your answers in the spaces provided.

[ 4 ]

[Maximum number: 7]

A compound Q contains the elements carbon, hydrogen and oxygen only.

The high resolution proton NMR spectrum of Q is shown.

Deduce the structure of Q. Justify your answer by considering the relative peak areas, the chemical shifts and the splitting patterns.

You will find it helpful to refer to page 8 of the Data Booklet.
The peak at 3.6 ppm is due to a proton environment on a carbon bonded to the benzene ring. The peak is not where it might be expected from the general values in the Data Booklet.

SECTION C

Answer ALL the questions. Write your answers in the spaces provided.

Exam points

Question 2

Question 2(b)

Question 2(c)

Question 2(d)

Question 2(d)(i)

Question 2(d)(ii)

Question 2(d)(iii)

Question 12(a)

Question 6(a)

Question 19

Question 19(a)(i)

Question 19(a)(iii)

Question 19(b)

Question 20

Question 20(a)

Question 20(a)(iii)

Question 20(c)

Question 21

Question 21(b)

Question 21(b)(i)

Question 21(b)(ii)

Question 15(b)