C 13 NMR.pdf

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1. MCH-401:Application of Spectroscopy (Organic)
UNIT-4th: Carbon-13 NMR Spectroscopy
Prof.Anand Halve
S.O.S in Chemistry
Jiwaji University Gwalior

2. C. NMR Spectroscopy
1. General Theory
2.13C NMR
3.1H NMR

3. 1.General Theory of NMR
A magnetic field is generated by a spinning charge
The nucleus of many atoms is a spinning charge.

4. For many nuclei, an external magnetic field will cause
the spinning charge to either line up with
the external magnetic field or against it

5. The βspin state is slightly greater in energy.
The difference in energy between αand βincreases
with increasing magnetic field strength.

6. Nuclei can absorb energy.
When nuclei in the αstate absorb radiation
equal in E to the difference between the α
and βspin states, the αspin state is
promoted to the βspin state.
The radiation required for “spin flipping”
has a frequency in the radio wave range

7. Nuclei can emit energy.
As nuclei move from
the βspin state to theαspin state,
energy is emitted and the frequency of that
energy can be detected.
resonance = nuclei flipping back and forth
between the αand βspin state.

8. Resonance is the “Song of the Nuclei.”
Every molecule sings its own song
as a result of its structure.

9. Analysis of an NMR spectrum
may involve analyzing:
a) The number of signalsa molecule emits
b) The frequenciesat which signals occur
c) The intensityof signals
d) The splittingof signals

10. 2. 13C NMR
a) Number of signals
b) Position of signals
c) DEPT data

11. a) The number of signals correlates
with the number
types of carbon
in a molecule

12. cyclopentane

13. 13C-NMR cyclopentane

14. Pentane
CH3CH2CH2CH2CH3

15. 13C-NMR pentane

16. 13C-NMR hexane

17. 13C-heptane

18. 13C-NMR chlorocyclopentane

19. 13C-NMR 2,2-dimethylpropanal
O
C
H
CH3
CCH3
CH3

20. 13C-NMR 2-methylbutane

21. 13C-NMR toluene

22. (Z)-3-methyl-2-pentene

23. (E)-3-methyl-2-pentene

24. Consider C4H9Br
Which isomers are represented by
these spectra?

25. b) The positions of signals
correlate with the extent of
shielding and deshielding
by electrons
experienced by each C nucleus

26. Diamagnetic Shielding
The greater the electron density
around a C nucleus, the lower
the effective magnetic field
around that C nucleus.
Needs lower frequency for
resonance
The carbon nucleus is
“shielded”

27. Carbon nuclei adjacent to
electronegative atoms experience a lower
e-cloud density
These carbons are “deshielded”
and require greater frequencies for
resonance.

28. carbons carbons

29. Chemical Shift
The frequency at which a nucleus will resonate is
dependent on the magnetic field strength.
Because this can vary from instrument to
instrument, frequency is expressed relative to
magnetic field strength, “chemical shift”
Chemical Shift = frequency of resonance (Hz)
frequency of instrument(MHz)
units = parts per million = ppm

30. 13C Chemical Shift Correlation Chart

32. pentane

33. hexane

34. cyclopentane

35. ethyl bromide

36. n-propyl chloride

37. ethanol

38. 2-propanol

39. O

40. ethyl propyl ether

41. Ethyl amine

42. Acetaldehyde

43. 2,2-dimethylpropanal
O
C
H
CH3
CCH3
CH3

44. Acetone
O
C
H3C CH3

45. 2-pentanone
O

46. acetic acid

47. Propionic acid

48. methyl propionate

49. Acetamide

50. N-methyl acetamide

51. 1-pentene

52. (Z)-3-methyl-2-pentene

53. (E)-3-methyl-2-pentene

54. 2-butyne

55. Benzene

56. toluene

57. Benzaldehyde

58. c) DEPT data
DEPT = distortionless enhancement by polarization
Distinguishes:
CH3-methyl groups
-CH2-methylene groups
I
-CH-methine groups
I
-C- 4ocarbons ( not detected by DEPT)
I

59. DEPT 13C spectrum of citronella
C10H16O

60. C4H10O
CH3
4oC

61. C4H10O

62. C4H10O
CH3
4oC

63. C5H10O
CH2
CH3
4oC

64. C5H10O

65. C5H10O
CH2
CH3
4oC

66. C4H8O2
CH2
CH3
4o C CH3

67. C4H8O2

68. C4H8O2
CH2
CH3
4o C CH3

69. C8H9Br
Both CH
CH2
4oC4oC
CH3

70. C8H9Br

71. C8H9Br
CHCH
CH2 CH3
4oC4oC

72. Both C3H6O2
CH2
4oC
A
4oC
CH3
CH3
CH2
B

73. A
B

74. C3H6O2
CH2
4oC
A
4oC
CH3
CH3
CH2
B

75. 1H NMR
CH3COCH2OH
CH3CH2COOH