NMR Spectroscopy

Question 1

Why is NMR such a powerful technique?

Answer 1

• it is easy to obtain a spectrum
• only a small amount of sample is necessary
• it is non-destructive (the sample being tested can be used again)

Question 2

For 13-CNMR, what is the rule of thumb relating to how close a carbon is to an electronegative atom?

Answer 2

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

Question 3

TMS is the abbreviation for what molecule?

Answer 3

tetramethylsilane

Question 4

Where does TMS peak?

Answer 4

at 0.0 ppm

Question 5

What is the purpose of TMS?

Answer 5

It is used as a reference standard for chemical shifts. All peaks generated by the sample have a chemical shift relative to the peak caused by TMS at 0.0 ppm

Question 6

Why is TMS used as a standard?

Answer 6

• it generates one sharp peak
• it is unreactive so won’t affect the sample being analysed
• it is highly volatile, meaning it can be removed from the sample being tested after the analysis fairly easily

Question 7

What are some common examples of solvent used?

Answer 7

CDCl3 (deuterated trichloromethane)
C6D6 (deuterated benzene)
CCl4

Question 8

Why are these examples of solvents used?

Answer 8

the solvents used cannot contain any H atoms - instead solvents using deuterium atoms are used (it has one proton and one neutron so doesn’t create a peak on the spectrum) or it doesn’t contain any H atoms to start with