1. Chemsheets AS006 (Electron arrangement)
10/05/2019
NMR
SPECTROSCOPY

2. 1H NMR
SPECTROSCOPY

3. NUCLEAR SPIN
Protons and neutrons can be regarded as spinning about their axis.
In many atoms these spins are paired against each other and so the nucleus has no overall spin (e.g. 12C).
In some atoms (e.g. 1H and 13C) the nucleus has an overall spin.
A nucleus that spins generates a magnetic field.
The direction of the magnetic field depends which way the nucleus spins.

4. Applied magnetic field
NUCLEAR SPIN
Usually the two possible spin states of the nucleus have the same amount of energy.
However, in a magnetic field, the two spin states have different energies.
Energy
Magnetic field opposed to applied field
Applied magnetic field
Energy gap corresponds to frequency of radiowaves
Magnetic field in same direction as applied field

5. butanone

6. EQUIVALENT H's
In a spectrum, there is one signal for each set of equivalent H atoms i.e. those H atoms in the same environment
The intensity or area of each signal being proportional to the number of equivalent H atoms it represents.

7. To identify hydrogen environments we need to look at the molecule:
Draw out the molecule in full.
Circle the first environment in one colour
Circle the next environment in another colour
Continue this process till there are no more hydrogen environments
Then work out the number of protons in each hydrogen environment to give you the peak ratio`s (peak areas).

8. 2 sets of equivalent H’s: ratio 6:2 (3:1)

9. For each of the following compounds, predict the number of signals and the relative intensity of the signals.
a) methylpropene
propene
2-chloropropane
propanone
methylamine
ethyl propanoate
1,2-dibromopropane
dimethylethyl propanoate
but-2-ene

10. 2 signals: ratio 6:2 (3:1)
1 signal
3 signals: ratio 2:1:3
2 signals: ratio 3:2
2 signals: ratio 6:1
4 signals: ratio 3:2:2:3

11. 3 signals: ratio 2:1:3
3 signals: ratio 3:2:9
2 signals: ratio 6:2 (3:1)

12. SOLVENTS & CALIBRATION
Samples are dissolved in solvents free of 1H atoms, e.g. CCl4, CDCl3.
A small amount of TMS (tetramethylsilane) is added to calibrate the spectrum.
It is used because:
its signal is away from all the others
it only gives one signal
it is non-toxic
it is inert
it has a low boiling point so is easy to remove

13. CHEMICAL SHIFT
The d is a measure in parts per million (ppm) of how far the magnetic field required for absorption is shifted away from that for TMS.
The d depends on what other atoms/groups are near the H – more electronegative groups gives a greater shift.

14. Number of H’s next door +1
SPIN-SPIN COUPLING
Coupling / Splitting / Multiplicity
Number of H’s next door +1

15. Data from AQA datasheet

16. This is the table that should be used when doing questions on NMR
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern

17. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1

18. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3

19. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3

20. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3

21. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet

22. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2

23. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2

24. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2

25. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2

26. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2
quartet

27. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2
quartet

28. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2
quartet

29. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2
quartet

30. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2
quartet

31. 2 1 3 Example 1 Hydrogen Environment Number Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 3
triplet 2
quartet

32. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1

33. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6

34. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6

35. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6

36. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet

37. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet 2

38. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet 2

39. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet 2

40. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet 2

41. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet 2
multitet

42. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet 2
multitet 3

43. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet 2
multitet 3

44. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet 2
multitet 3

45. Example 2 3 4 1 2
Hydrogen Environment Number
Number of Hydrogens
Ratio (peak area)
Splitting Pattern 1 6
doublet 2
multitet 3
quartet 4
triplet

46. n+1 0 H next door singlet (s) 1 H next door doublet (d) 2 H next door
triplet (t)
3 H next door
quartet (q)
more H next door
multiplet (m)

47. SPIN-SPIN COUPLING signal singlet doublet triplet quartet appearance
number of lines 1 2 3 4
number of H’s next door

52. Number of H’s next door +1
But you don’t couple to
H’s that are equivalent
H’s on O’s

53. SUMMARY Number of signals Position of signals Relative intensities
Splitting
how many different sets of equivalent H atoms there are
information about chemical environment of H atom
gives ratio of H atoms for peaks
how many H atoms on adjacent C atoms

54. For each of the following compounds, predict the number of signals, the relative intensity of the signals, and the multiplicity of each signal.
a) methylpropene
propene
2-chloropropane
propanone
methylamine
ethyl propanoate
1,2-dibromopropane
dimethylethyl propanoate
but-2-ene

55. 2 peaks: ratio 6 : 2 (3 :1)
s s
1 signal
3 signals: ratio 2 : 1 : 3
d m d
2 signals: ratio 3 : 2
t q
2 signals: ratio 6 : 1
d m
4 signals: ratio 3 : 2 : 2 : 3
t q q t

56. 3 signals: ratio 2 : 1 : 3
d m d
3 signals: ratio 3 : 2 : 9
t q s
2 signals: ratio 6 : 2 (3 :1)
d q