C and H NMR Spectra

Question 1

C NMR content:
the closer the atom to a very electronegative atom/double bond, the greater the chemical shift

IMPORTANT: no splitting of the lines in the graph

Question 2

H NMR content:

the sample is dissolved in solvents that contain NO H ATOMS eg CCl4 and deuterated solvents like CDCl3 –> they contain ‘D atoms’ which have no spin and won’t show up in the spectra.

Splitting of lines is calculated by: n+ 1, with n being the number of H atoms in the adjacent carbon.

Question 3

What substance is used to calibrate/standard a C/H NMR spectra?

Answer 3

tetramethylsilane (TMS)

use a small quantity of TMS to produce a signal which will provide a standard to which other peaks are compared.

TMS is used because:
* only gives one signal
* non-toxic
* inert
* has a low boiling point (26 degrees) - can be easily removed via distillation
* gives a signal which is furthest to the right than most of the signals in an organic compound.

Question 4

What are the common signals to look out for in H NMR?

Answer 4

Question 5

What are the meanings of the splitting of the lines in H NMR?

Answer 5

singlet: no H atoms are on the adjacent (next) carbon

doublet: only 1 H atom are on the adjacent (next) carbon - ‘CH group’

triplet: only 2 H atoms are on the adjacent (next) carbon - ‘CH2 group’

quartet: only 3 H atoms are on the adjacent (next) carbon - ‘CH3 group’

multiplet: multiple H atoms are on the adjacent (next) carbon

Question 6

What does the relative intensity of the signals mean?

Answer 6

It means the number of H atoms that are on that carbon/signal.