Module 6 - Analysis/NMR

Question 1

What does NMR stand for?

Answer 1

Nuclear Magnetic Resonance

Question 2

What does TMS stand for?

Answer 2

Tetramethylsilane

Question 3

What is TMS used for?

How?

Answer 3

• TMS is the reference used to create the reference peak on and NMR spectra
• Has 12 protons - creates a sharp peak on and NMR spectra

Question 4

Why are deuterated solvents used?

Answer 4

• Hydrogens are replaced with Deuterium (2H isotope of hydrogen)
• This doesn’t produce a signal in the NMR range

Question 5

What is deuterium?

Answer 5

An isotope of hydrogen with 1 proton and 1 neutron - (2)H - has a relative atomic mass of 2

Question 6

What is the deuterium test in NMR used for?

Answer 6

Prove we have an alcohol or amine group attached to our structure

Question 7

What is NMR used for?

Answer 7

Used to assess the environment around a given (Hydrogen) atom.
Can show us what atoms are bonded to the hydrogen atoms
Peaks show a differently bonded hydrogen atom bonded in the molecule

Question 8

Chemical shift use

Answer 8

Tells us the type of environment each proton exists in

Question 9

Effect of chemical shifts

Answer 9

• Protons attached to more electronegative atoms will be shifters more downfield (higher ppm)
• Protons in the same environment will have the same chemical shift

Question 10

Is deuterium observed in NMR (hydrogen NMR)

Answer 10

No.

Only hydrogen is (in hydrogen NMR)

Question 11

Spin-spin coupling

Answer 11

High resolution gives more complex signals

• These are:
• doublets
• triplets
• quartets
• multiplets
• The signal produced indicates the number of protons on adjacent carbon atoms
• The splitting pattern depends on the number of hydrogen atoms on adjacent atoms

Question 12

How to work out number of peaks in splitting during NMR

Give examples

Answer 12

No. Of peaks = no. Of chemically different Hydrogen atoms on adjacent atoms +
= n + 1

1 Neighbouring Hydrogen atom- 2 peaks - ratio: 1:1
2 Neighbouring Hydrogen atoms - 3 peaks - ratio: 1:2:1
3 Neighbouring Hydrogen atoms - 4 peaks - ratio: 1:3:3:1
4 Neighbouring Hydrogen atoms- 5 peaks - ratio: 1:4:6:4:1

Question 13

What do number of peaks on Carbon-NMR indicate?

Answer 13

Number of different carbon environments

Question 14

Explain the use of two deuterated compounds in NMR spectroscopy.
(2 Marks)

Answer 14

D2O - used to identify OH and NH functional groups

CDCl3 - used as solvent