[Maximum number: 2]

Serotonin can be synthesised from the amino acid tryptophan in two steps.

(a)

Serotonin is converted by enzymes in the liver to compound M.

[ 2 ]

(i)

The proton NMR spectrum of M dissolved in $\mathrm{CDCl}_{3}$ shows eight peaks due to the eight different types of proton present in the molecule.

The proton NMR spectrum of M dissolved in $\mathrm{D}_{2} \mathrm{O}$ was recorded.
Predict the number of peaks that would be seen in the proton NMR spectrum of M in $\mathrm{D}_{2} \mathrm{O}$ . Explain your answer.
number of peaks explanation

[ 2 ]

(a)

An ester of pyruvic acid, F, is dissolved in $\mathrm{CDCl}_{3}$ and analysed by proton NMR spectroscopy.

F

The proton NMR spectrum of F is shown.

Use the proton NMR spectrum of F to complete the table.

[ 3 ]

(b)

Deuterium oxide, $\mathrm{D}_{2} \mathrm{O}$ , where D is ${ }^{2} \mathrm{H}$ , can be used as a solvent in proton NMR spectroscopy. The proton NMR spectrum of alanine in $\mathrm{CDCl}_{3}$ has 4 peaks.
The proton NMR spectrum of alanine in $\mathrm{D}_{2} \mathrm{O}$ has 2 peaks.

alanine

On the diagram of alanine, circle the protons that show peaks in both NMR spectra. Explain your answer.

[ 2 ]

(a)

An ester of pyruvic acid, F, is dissolved in $\mathrm{CDCl}_{3}$ and analysed by proton NMR spectroscopy.

F

The proton NMR spectrum of F is shown.

Use the proton NMR spectrum of F to complete the table.

[ 3 ]

(b)

Deuterium oxide, $\mathrm{D}_{2} \mathrm{O}$ , where D is ${ }^{2} \mathrm{H}$ , can be used as a solvent in proton NMR spectroscopy. The proton NMR spectrum of alanine in $\mathrm{CDCl}_{3}$ has 4 peaks.
The proton NMR spectrum of alanine in $\mathrm{D}_{2} \mathrm{O}$ has 2 peaks.

alanine

On the diagram of alanine, circle the protons that show peaks in both NMR spectra. Explain your answer.

[ 2 ]

(a)

Complete Table 6.2 to predict the number of peaks in the proton $\left({ }^{1} \mathrm{H}\right)$ NMR spectrum for Dewar benzene, Ladenburg benzene and delocalised benzene.

Table 6.2

[ 1 ]

(a)

Three carboxylic acids, methanoic acid, $\mathrm{HCO}_{2} \mathrm{H}$ , ethanedioic acid, $\mathrm{HO}_{2} \mathrm{CCO}_{2} \mathrm{H}$ , and butanedioic acid, $\mathrm{HO}_{2} \mathrm{CCH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}$ , are compared. Two tests were carried out on separate samples of each organic acid, as shown.

The following results were obtained. ✓ = observed change x= no observed reaction

[ 1 ]

(i)

The proton NMR spectrum of $\mathrm{HCO}_{2} \mathrm{H}$ in $\mathrm{D}_{2} \mathrm{O}$ is obtained.

Describe and explain the difference observed between this spectrum and the proton NMR spectrum of $\mathrm{HCO}_{2} \mathrm{H}$ in (b)(ii).

[ 1 ]

[Maximum number: 3]

Butanedioic acid can be made in a three-step synthesis using ethane as the starting material.

ethane

A

B step 3

butanedioic acid

(a)

Methylpropanedioic acid is an isomer of butanedioic acid.

methylpropanedioic acid

The proton NMR spectrum of methylpropanedioic acid in $\mathrm{CCl}_{4}$ is shown. \begin{tabular}{|c|cccccc|c||c|}
\hline
\end{tabular}

[ 3 ]

(i)

Identify the protons in the methylpropanedioic acid molecule that are responsible for each area of the proton NMR spectrum.
$\delta 12.7$ $\delta 3.3$ $\delta 1.1$

[ 2 ]

(ii)

Name the splitting pattern shown at $\delta 3.3$ and explain how it arises.

The carbon-13 NMR spectra of butanedioic acid, $\mathrm{HO}_{2} \mathrm{CCH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}$ , and methylpropanedioic acid, $\mathrm{HO}_{2} \mathrm{CCH}\left(\mathrm{CH}_{3}\right) \mathrm{CO}_{2} \mathrm{H}$ are different.

[ 1 ]

[Maximum number: 2]

Gallic acid, $\mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}_{5}$ , is a naturally occurring aromatic molecule.

gallic acid

(a)

(i)

The proton NMR spectrum of gallic acid dissolved in $\mathrm{D}_{2} \mathrm{O}$ is recorded.
- Predict the number of peaks observed and any expected splitting pattern.
- State the expected chemical shift range $(\delta)$ of each peak predicted.

[ 2 ]

(a)

State the uses of TMS and $\mathrm{D}_{2} \mathrm{O}$ in NMR spectroscopy.
TMS
$\mathrm{D}_{2} \mathrm{O}$

[ 1 ]

(b)

The three isomeric ketones with molecular formula $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}$ are:
- pentan-2-one
- pentan-3-one
- 3-methylbutanone.

[ 2 ]

(i)

State all the ketones with molecular formula $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}$ that have:
a doublet in their proton $\left({ }^{1} \mathrm{H}\right)$ NMR spectrum
a singlet in their proton $\left({ }^{1} \mathrm{H}\right)$ NMR spectrum.

[ 2 ]

(a)

There are four structural isomers with the molecular formula $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}$ that are aldehydes.

[ 6 ]

(i)

Draw the structures of these aldehydes.
P
R
Q

(ii)

The NMR spectrum of one of these isomers contains four absorptions. Which isomer P, Q, R or S gives this spectrum?
isomer

(iii)

Predict the number of absorptions that would be given by each of the other three isomers.

[ 6 ]

(a)

Compound A can also be used to make the amide $\mathrm{CH}_{3} \mathrm{CONHC}_{2} \mathrm{H}_{5}$ .

The proton NMR spectrum of the amide $\mathrm{CH}_{3} \mathrm{CONHC}_{2} \mathrm{H}_{5}$ in the solvent $\mathrm{CDCl}_{3}$ is shown.

[ 5 ]

(i)

Explain why $\mathrm{CDCl}_{3}$ is used as a solvent instead of $\mathrm{CHCl}_{3}$ .

[ 1 ]

(ii)

Complete the diagram with the chemical shifts, $\delta$ , of the protons labelled in the $\mathrm{CH}_{3} \mathrm{CONHC}_{2} \mathrm{H}_{5}$ molecule.

[ 2 ]

(iii)

State and explain how the proton NMR spectrum of the amide $\mathrm{CH}_{3} \mathrm{CONHC}_{2} \mathrm{H}_{5}$ differs when dissolved in $\mathrm{D}_{2} \mathrm{O}$ rather than $\mathrm{CDCl}_{3}$ .

[ 2 ]