Proton NMR spectroscopy 90-91

Question 1

Why does proton NMR require far less material than carbon-13 NMR?

Answer 1

¹H nucleus has just a single proton in its nucleus and has a residual magnetic spin. ¹H is the commonest isotope of hydrogen, with a relative abundance of 99.9%. This is in contrast to ¹³C, which makes up just 1.1% of carbon atoms. Because of the greater abundance of ¹H nuclei, proton NMR requires far less material than ¹³C NMR.

Question 2

What does proton NMR tell you that carbon-13 NMR also tells you?

Answer 2

• The number of peaks gives the number of proton environments.
• The chemical shifts give the type of proton environment of each peak.

Question 3

What additional information does the proton NMR spectrum give (that ¹³C NMR doesn’t)?

Answer 3

• The relative peak areas give the proportions of protons in each environment.
• Spin-spin coupling gives information about adjacent protons.

Question 4

What are integration traces?

Answer 4

In a proton NMR spectrum, the area under each peak is in direct proportion to the number of protons responsible for the absorption.

• The spectrometer measures this area. This information can be displayed as an extra line on the NMR spectrum called an integration trace.
• The integration trace shows a series of steps, increasing in height as it passes each peak. The ratio of the step heights is equal to the ratio of each type of proton. The values for the integration steps can also be displayed on the spectrum, labelled ‘Integration’.