32 - Structure determination

Question 1

What does NMR stand for?

Answer 1

Nuclear magnetic resonance

Question 2

Name two types of NMR.

Answer 2

Proton
Carbon 13

Question 3

What does each peak in a C-13 NMR represent?

Answer 3

A different carbon environment. For example, two different carbon environments will give 2 peaks, irrelevant of the number of C atoms.

Question 4

What does each peak in a proton-NMR represent?

Answer 4

A different hydrogen environment.

Question 5

What is the integration value of each peak in proton NMR?

Answer 5

The number of H atoms in that environment.

Question 6

What type of solvent must proton NMR samples be dissolved in? Give a reason why and an example.

Answer 6

One which contains no H atoms
So it gives no peak in the NMR spectrum
CCl4

Question 7

What is the x axis on the NMR spectrum?

Answer 7

Chemical shift (ppm)

Question 8

What is used as a standard in NMR? Give 3 reasons why?

Answer 8

TMS
Only gives one signal
Far away from other compounds at 0
Low boiling point so easy to remove

Question 9

How is peak splitting defined in high resolution proton NMR?

Answer 9

(Number of non-equivalent protons on adjacent carbons) + 1

The non-equivalent thing is basically irrelevant though, it’s just any protons.

Question 10

What the chemical formula of TMS?

Answer 10

Si(CH3)4

Question 11

Why are CCl4 and CDCl3 good solvents?

Answer 11

No hydrogen so give no peaks
Inert

CCl4 is non-polar, so good for non-polar organic molecules
CDCl3 is polar, so good for polar organic compounds