Spectroscopy exercises SL PDF

Preview

Summary

Excersises for Spectroscopy SL...

Description

Spectroscopy exercises 1a. [1 mark] The structure of an unknown compound A with empirical formula information from a variety of analytical techniques. The mass spectrum of A is shown below.

Deduce the formula of the molecular ion from the mass spectrum. 1b. [1 marks] The infrared (IR) spectrum of A is shown below.

Explain the band labelled B in the IR-spectrum. 1

can be determined using

1c. [1 mark] One isomer of A has only one signal in its

NMR spectrum. Deduce the structural formula of this isomer.

2. [3 marks] NMR spectroscopy is one of the most powerful analytical tools for determining molecular structure. The 1H NMR spectrum, including the integration trace, of a ketone with relative molecular mass 86 is shown below.

[Source: SDBS web: www.sdbs.riodb.aist.go.jp (National Institute of Advanced Industrial Science and Technology, 2014)] Deduce the structural formula of the compound, justifying your choice. 3a. [2 marks] Consider the compound chloroethene, CH2=CHCl. Deduce two features you would expect to observe in its mass spectrum. 3b. [2 marks] Predict two features you would expect to observe in its infrared (IR) spectrum.

2

4a. [1 mark] Compound X has the molecular formula

and is found in human perspiration.

Its infrared (IR) spectrum is represented below.

Deduce the bonds responsible for the absorptions labelled I and II.

I:

II: 4b. [1 mark] The

spectrum recorded showed four peaks with the following chemical shift values (in ppm):

3

The integration trace for A:B:C:D was found to be 1:1:1:3. Deduce what information can be obtained about the hydrogen atoms responsible for peak D at 1.2 ppm from the integration trace in the

spectrum of X.

4c. [2 marks] Deduce the fragments in the mass spectrum which correspond to the following

values.

: : :

4d. [1 mark] Deduce the structural formula of X. 4e. [1 mark] Y is an isomer of X, which contains the same functional groups. Deduce the structural formula of Y. 5. [2 marks] Three isomers of

are ethyl methanoate, methyl ethanoate and propanoic acid.

4

Explain which of the three compounds has a

spectrum showing two peaks with equal areas

under each peak. 6a. [1 mark] Compound P contains a carbonyl group (C=O) and has the molecular formula C 3H6O. Draw the two possible structures of compound P. 6b. [1 mark] Explain why the infrared spectra of the structures in (a) are very similar.

5

6c. [2 marks] Explain how the mass spectra of the structures in (a) can be used to distinguish between them. 6d. [3 marks] Pentan-2-one has the following mass spectrum.

Deduce the formulas of the species with the m/z values at 86, 71 and 43.

: : : 6e. [1 mark] Suggest a reason for the peak at m/z = 43 having an exceptionally high relative abundance.

6...