3.3.15 NMR Spectroscopy

Question 1

What is NMR? (3)

Answer 1

Nuclear magnetic resonance
C-13 - gives information about arrangement of carbon atoms
H-1 - gives information about arrangement of hydrogen atoms

Question 2

What is chemical shift (δ)?

Answer 2

The difference in energy absorbed by nuclei in different environments relative to a standard (ppm)

Question 3

What is the standard used for NMR spectroscopy? (3)

Answer 3

TMS (tetramethylsilane)
Inert, non-toxic, volatile (easy to remove from sample)
Produces a single absorption peak away from other peaks (δ = 0)

Question 4

What does a carbon NMR spectrum show? (2)

Answer 4

Number of peaks indicates number of carbon environments

Carbons with a higher chemical shift are less shielded as they are close to more electronegative atoms

Question 5

What does a proton NMR spectrum show? (3)

Answer 5

Each peak shows number of hydrogen nuclei in a particular environment
Relative area of peaks shows ratio of atoms in each environment
The peaks are split into multiplets. If there are n hydrogen atoms in the adjacent environment, the peak splits into n+1 parts

Question 6

How are samples dissolved for proton NMR?

Answer 6

In solvents that do not contain any H atoms (deuterated solvents (e.g. D2O) or compounds such as CCl4