Structure determination

Question 1

What is the theory behind NMR?

Answer 1

Nuclei with odd mass numbers have a property known as spin. They generate a magnetic field. Magnets orientate parallel or anti-parallel to the magnetic field. A difference in energy between orientations is dependent on the size of the external magnetic field. The size of the difference varies from molecule to molecule and is measured via NMR

Question 2

What is the definition of resonant frequency?

Answer 2

The frequency required to cause the flipping of a particular magnetic field.

Question 3

What is the chemical shift?

Answer 3

Question 4

What are the axes of an NMR spectrum?

Answer 4

Energy absorbed on the y-axis

Chemical shift on x-axis/ppm

Question 5

What do peaks represent in both proton and carbon NMR?

Answer 5

The position of the peaks represent the different environments in both carbon and proton NMR., However, in proton NMR the area of each peak is proportional to the number of hydrogens in the environment.

Question 6

How does splitting work?

Answer 6

n+1 rule

One hydrogen on an adjacent carbon then peak splits into two.

2 hydrogens on adjacent peaks, the peak will split into 3 heights in a ratio of 1:2:1

3 adjacent peaks cause the peak to split into 4 peaks in ratio 1:3:3:1

Question 7

What is the reference standard?

Answer 7

Tetramethylsilane