NMR spectroscopy

Which compound(s) has/have three peaks in their¹³C NMR spectrum?

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

This question is about spectral analysis.

Compound K, C₄H₁₀O, is refluxed with H₂SO₄ to form a mixture of compound L and compound M.

The infrared spectrum of compound K is shown.

Compound L and compound M are analysed using¹³C NMR spectroscopy.

• The¹³C NMR spectrum of compound L has 4 peaks.

• The¹³C NMR spectrum of compound M has 2 peaks.

Suggest the functional group in compound K, showing your reasoning, and suggest possible structures for compound K, compound L and compound M.

Functional group........

* An unknown organic compound N is analysed and produces the following results.

Elemental analysis by mass

C, 62.07%; H, 10.34%; O, 27.59%

Mass spectrum

The numbers by the peaks are the relative peak areas.

Determine the structure of the compound N, showing all your reasoning.

This question is about spectra.

The mass spectrum for Br₂ has peaks at m/z values of 79, 81, 158, 160 and 162. The peaks at m / z 79 and 81 have virtually the same relative abundance.

Complete the table to show the number of protons, neutrons and electrons in the particles that cause the peaks at m/z 79 and 81.

Explain why there are peaks with m / z values of 158, 160 and 162 and predict their relative abundances.

Explanation........

Relative abundances........

This question looks at proton NMR spectra of dibromoalkanes.

Which compound is used for proton exchange in NMR spectroscopy?

A CCl₄

B CDCl₃

C D₂O

D Si(CH₃)₄

Which compound has the greatest number of peaks in its proton NMR spectrum?

This question is about alcohols.

An unsaturated alcohol has 6 carbon atoms and contains one C=C bond.

Construct an equation for the complete combustion of this alcohol.

Compound C, shown below, is refluxed with excess acidified potassium dichromate(VI) to form a single organic product and one other product.

Complete the equation for this reaction.

Compound C

Draw the structures of the three isomers of C₇H₁₀ formed from compound D.

A student converts compound D into a diiodoalkane.

Suggest suitable reagents for this reaction.

There are 4 structural isomers of C₄H₁₀O that are alcohols.

A student predicts that these structural isomers could be distinguished using carbon-13 NMR spectroscopy.

Explain whether the student is correct.

In your answer, show how the peaks in the carbon-13 NMR spectra are linked to the structure of each alcohol isomer.

Which compound produces two triplets in its¹H NMR spectrum?

A CH₃CH₂COOCH₂CH₃

B CH₃CH₂COCH₂CH₃

C HOOCCH₂CH₂COOH

D HOOCCH₂CH₂CH₂COOH

Which isomer(s) of C₅H₁₂O has/have 4 peaks in its/their¹³C NMR spectrum?

1 3-methylbutan-2-ol

2 2-methylbutan-2-ol

3 2-methylbutan-1-ol

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

This question is about carbonyl compounds.

Describe a chemical test to confirm the presence of a carbonyl group.

How could the product of this test be used to identify the carbonyl compound?

Your answer should not include spectroscopy.

Describe a chemical test that would identify whether a carbonyl compound is an aldehyde.

Your answer should include the reagent and observations.

A student is provided with two unknown carbonyl compounds, F and G.

The compounds are analysed and found to have identical percentage compositions by mass: C: 62.07%; H: 10.34%; O: 27.59%

The mass spectra of the two compounds are shown below.

Use the results to identify the structures of the two compounds.

Include relevant peaks present in the mass spectrum of each compound.

This question is about the chemistry of aromatic compounds.

What chemical test(s) could be used to confirm the presence of the phenol group in compounds K and L ?

A student thought that¹³C NMR spectroscopy could be used to distinguish between compounds J, K and L.

Explain, with reasoning, whether the student is correct.

Compound J is substituted at the 2-and 4-positions by chlorine in the presence of a catalyst.

Outline the mechanism for the 4 substitution of compound J by chlorine in the presence of a catalyst.

Show the role of the catalyst.

Compounds K and L react with chlorine much more readily than compound J.

Explain why.

Compound J, C₆H₅CH₂CH₂OH, is reacted with acidified potassium dichromate(VI) under reflux to form organic product M.

Write an equation for this reaction.

Use [O] to represent the oxidising agent and show the structure of M.

A two-stage synthesis of an amine from compound J is shown below.

Add the reagents for each stage of this synthesis.

Compound J

These questions are from different areas of chemistry.

Ammonia, NH₃, and ammonium nitrate, NH₄NO₃, are compounds of nitrogen.

The boiling point of NH₃ is –33 °C.

The boiling point of NH₄NO₃ is 210 °C.

Explain why there is a large difference in boiling points.

Two students discuss the oxidation numbers in ammonium nitrate, NH₄NO₃.

One student claims that the two nitrogen atoms have the same oxidation number. The other student disagrees and claims that the nitrogen atoms have different oxidation numbers.

Explain with reasons which student is correct.

What are the percentage compositions of copper and zinc in the brass sample?

Calculate the relative atomic mass of zinc in the sample of brass.

Give your answer to 2 decimal places.

Fill in the table to predict the splitting patterns in the proton NMR spectrum of the

The table shows the chemical shifts for the peaks in the proton NMR spectrum at proton environments 2 and 3.

Proton environment	2	3
Chemical shift,	2.5 ppm	3.6 ppm

Suggest why the peaks for proton environments 2 and 3 have the chemical shifts which are shown in the table.

Glycine, H₂NCH₂COOH, is an -amino acid.

Glycine reacts with NaOH to form the salt H₂NCH₂COONa.

Glycine reacts with HCl to form the salt HOOCCH₂NH₃Cl.

The salts have different H–N–H bond angles.

State the different H–N–H bond angles and explain why they are different.

H₂NCH₂COONa H–N–H bond angle =........ °

HOOCCH₂NH₃Cl H–N–H bond angle =........ °

Glycine reacts with aqueous copper(II) ethanoate to form copper(II) glycinate, Cu(H₂NCH₂COO)₂, and ethanoic acid. Copper(II) glycinate is a complex which exists as two square planar isomers.

Write an equation for this reaction and draw the structures of the two square planar isomers of the complex Cu(H₂NCH₂COO)₂.

equation

Which compound(s) has/have four peaks in a¹³C NMR spectrum?

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Which isomer of C₆H₁₂O₂ produces the smallest number of peaks in its¹³C NMR spectrum?

Compounds B and C, shown below, are unsaturated hydrocarbons containing nine carbon atoms.

Compound B reacts with chlorine at room temperature, but compound C requires the presence of a halogen carrier.

In both reactions, the organic compound reacts with chlorine in a 1:1 molar ratio.

Draw the structures of the organic product of each reaction.

Outline the mechanism for the reaction of compound C with chlorine.

Show the role of the halogen carrier.

Compound C can be prepared by ‘trimerisation’ of propanone using concentrated sulfuric acid as a catalyst.

Suggest an equation for this reaction, using molecular formulae.

An organic chemist is investigating compound D for possible use as a medicine.

The chemist proposes a synthesis of compound D from compound C.

The chemist develops a three-stage synthesis of compound D from compound C.

Complete the flowchart. Show structures for organic compounds.

An organic compound I is analysed, using a combination of techniques. The analytical data is shown below.

Elemental analysis by mass C, 56.69%; H, 7.09%; N, 11.02%; O, 25.20%

Mass spectrum Molecular ion peak at m / z = 127.0

IR spectrum

Proton NMR spectrum

Explain the use of two deuterated compounds in NMR spectroscopy.

* Determine the structure of compound I, showing all your reasoning.

This question is about organic chemistry.

This part is about two practical techniques used in organic preparations.

Complete the missing labels on the diagram and name the technique.

Name of technique:........

Draw a labelled diagram to show apparatus set up for filtration under reduced pressure (vacuum filtration).

This part is about amines.

Amine A is a liquid at room temperature and pressure.

When vaporised, 0.202 g of the amine produces 72.0 cm³ of gas at 1.00 × 10⁵ Pa and 100 °C. The¹³C NMR spectrum of amine A has 3 peaks.

Determine the molecular formula of A and suggest a possible structure for amine A.

Molecular formula of A........

Structure of A

Which compound shows 4 peaks in its carbon-13 NMR spectrum?

A compound produces the¹³C NMR spectrum below.

Which compound could have produced this spectrum?

A Propane

B 2-Methylbutane

C 2-Methylpropan-1-ol

D 2-Methylpropan-2-ol

This question is about esters.

The structure of ester A is shown below.

What is the systematic name of ester A ?

Name the type of reactions of ester A shown in (ii).

A polyester is formed from 200 molecules of 4-hydroxybenzoic acid.

What is the relative molecular mass, M_r, of the polyester?

M_r =........ g mol⁻¹

* A student intends to synthesise ester C.

Plan a two-stage synthesis to prepare 12.75 g of ester C starting from 2-methylpropanal, (CH₃)₂CHCHO. Assume the overall percentage yield of ester C from 2-methylpropanal is 40%.

In your answer include the mass of 2-methylpropanal required, reagents, conditions and equations where appropriate.

Purification details are not required.

Dettol ® is a disinfectant containing the antiseptic chloroxylenol, shown below.

Chloroxylenol is a weak Brønsted–Lowry acid.

What is the systematic name of chloroxylenol?

Predict the number of peaks in a¹³C NMR spectrum of chloroxylenol.

Name the functional group responsible for the acidity of chloroxylenol and describe a simple test which would confirm the presence of this group.

Functional group........

Test........

A student measures the pH of the contents in a bottle of Dettol ® as 5.14.

The label on the bottle shows the percentage of chloroxylenol in Dettol ® as 4.80% i.e. 100 cm³ of Dettol^® contains 4.80 g of chloroxylenol.

Assume the following:

• Chloroxylenol is the only acidic component in Dettol ®.

• Chloroxylenol is a weak monobasic acid.

• The density of Dettol ® is 1.00 g cm −3.

Write the equation, using molecular formulae, for the acid dissociation of chloroxylenol.

Calculate the acid dissociation constant, K_a, for chloroxylenol.

K_a =........ mol dm⁻³

Dettol^® contains other chemicals including -terpineol, shown below.

-Terpineol is a chiral compound.

Show with an asterisk, (*), the chiral centre(s) in the structure of -terpineol.

-Terpineol meets the requirements for E / Z isomerism. However, only one E / Z isomer of -terpineol exists.

Explain

• why -terpineol meets the requirements for E / Z isomerism

• whether -terpineol is an E- or Z- isomer

• why only one E / Z isomer of -terpineol exists.

-Terpineol contains two functional groups.

For each functional group, choose a reagent that reacts with that group only. Draw the structures for the organic products of the reactions.

Show structures for organic compounds.

Reagent(s)........

Name of functional group that reacts........

Structure of organic product

Reagent(s)........

Name of functional group that reacts........

Structure of organic product

Which compound is used as a standard for NMR chemical shift measurements?

A Si(CH₃)₄

B CDCl₃

C D₂O

D CCl₄

What is the number of peaks in the¹H NMR spectrum of HOOCCH₂CHOHCH₂COOH?

A 3

B 4

C 5

D 6

This question is about aromatic compounds.

Phenol undergoes nitration more readily than benzene.

A student carries out the nitration of phenol with dilute nitric acid to produce 2-nitrophenol and 4-nitrophenol.

A small amount of 3-nitrophenol is also produced.

2-nitrophenol 3-nitrophenol 4-nitrophenol

The student thought that¹³C NMR spectroscopy could be used to distinguish between these three nitrophenols.

Explain whether the student is correct.

Explain why phenol is nitrated more readily than benzene.

Methylbenzene reacts with sulfur trioxide, SO₃, to form D, shown below.

The electrophile in this reaction is SO₃.

Complete the mechanism for the formation of D. Show curly arrows and the structure of the intermediate.

The relative molecular masses and boiling points of some fuels are shown in Table 22.1.

Write an equation for the incomplete combustion of heptane.

Explain the difference in the boiling points of the fuels in Table 22.1.

Fuel additives are often used to improve the combustion of a fuel.

Compound N is a fuel additive containing carbon, hydrogen and oxygen only.

Complete combustion of 1.71 g of compound N produces 2.97 g of CO₂ and 1.62 g of H₂O. The relative molecular mass of compound N is 76.0.

Calculate the molecular formula of N and suggest a possible structure for the compound.

compound N

Solketal has been investigated as a potential fuel additive.

Solketal is synthesised from propane-1,2,3-triol and a carbonyl compound.

Construct a balanced equation for this synthesis. Show structures for the organic compounds in your equation.

* A scientist is researching compounds that might be suitable as fuel additives. One of the compounds gives the analytical results below.

Elemental analysis by mass: C: 54.54%; H: 9.10%; O: 36.36%

Mass spectrum: Molecular ion peak at m / z = 132.0

¹H NMR spectrum in D₂O

The numbers by the peaks are the relative peak areas.

When the spectrum is run without D₂O, there are two additional peaks with the same relative peak areas at 11.0 ppm and 3.6 ppm.

Use the information provided to suggest a structure for the compound.

Show all your reasoning.

The compound below is analysed by¹H NMR spectroscopy.

How many peaks are observed in the¹H NMR spectrum?

A 5

B 4

C 3

D 2