Interpreting proton NMR spectra

Question 1

What is spin-spin coupling?

Answer 1

• if you zoon in on most NMR peaks, they are split into particular patterns

Question 2

Why does spin-spin coupling occur?

Answer 2

• the applied magnetic field felt by any hydrogen atom is affected by the magnetic field of the hydrogen atoms on the neighbouring carbon atoms
• this spin-spin splitting gives information about the neighbouring hydrogen atoms

Question 3

What is the n + 1 rule?

Answer 3

• n hydrogen on an adjacent carbon atom will split a peak into n + 1 smaller peaks

Question 4

What are the ratios for the peak splits?

Answer 4

• 1 hydrogen on adjacent carbon
  
  • split the NMR signal of a particular hydrogen into two peaks of the same height
• 2 hydrogen on adacent carbon
  
  • height ratio 1:2:1
• 3
  
  • 1:3:3:1

Question 5

What solvent is used for NMR? Why are they used?

Answer 5

• tetrachloromethane
• must not contain 1H, otherwise it would swamp the signal from hydrogen atoms in the sample because there are more
• other solvents contain deuterium, isotope of hydrogen
  
  • does not produce a NMR singla in same range as hydrogen

Question 6

What are the uses for predicting NMR spectrA?

Answer 6

• test sample and compare to prediction to ensure that the reaction has gone as intended