NMR

Question 1

Why is NMR so useful

Answer 1

• it is easy to obtain a spectrum
• only small amounts of sample are necessary
• it is non-destructive

Question 2

relationships between electronegativity and chemical shift

Answer 2

The closer to an electronegative atom, the higher the chemical shift of that carbon

Question 3

Tetra methyl silane and why it is used

Answer 3

4 carbon atoms which give ruse to a sharp peak at 0ppm
- used as a reference for chemical shifts.
- generated one sharp peak
- it is unreactive so won’t affect the sample being analysed
- highly volatile so can easily be removed from the sample
- peak always found in the far right of the spectrum

Question 4

What does each thing tell you on a proton NMR

Answer 4

• number of peaks tells you the different number of proton environments
• location of peaks shows the type of proton environment
• area under the peak tells you the number of protons in each environment
• the splitting shows the number of protons in adjacent environments
• integration ratios tell you how many protons each peak represents

Question 5

Solvents used in NMR

Answer 5

• needs to be dissolved in a solvents before it is analysed
  Deuterium is used- an isotope of hydrogen with a mass number of 2, doesn’t create a peak in NMR
  Deuterated trichloromethane: CDCl3 for polar samples
  Deuterated benzene: C6D6 for non-polar samples
  Alternatively solvent molecules with no hydrogen atoms to start with could be used like tetrachloromethane