nmr

1. 1
NMR Spectroscopy
BY
Dr. Suman Pattanayak
Associate Professor
Department of Pharma Analysis & QA.
Vijaya Institute of Pharmaceutical Sciences for Women
M. Pharm/ I Sem
Pharmaceutical Analysis

2. INTRODUCTION:-
NUCLEAR MAGNETIC RESONANCE
(NMR Spectroscopy)
 It is concerned with the magnetic properties of certain atomic
nuclei.
 Involves change in the spin state at the nuclear level.
SPINNIG NUCLEUS:
 proton acts as a tiny spinning
bar magnet and possesses both
electrical charge and mechanical spin.
2

3. SHELDING & DESHELDING
 The proton is shielded when the induced field opposes the applied
field.
 Higher the shielding of protons lower will be the value of δ.
 The proton is deshielded when the induced field reinforces the
applied field.
 Greater the deshielding higher will be the value of δ.
3

4. CHEMICAL SHIFT
 Each different hydrogen environment will appear in a different
position in the NMR spectrum. This is called Chemical Shift.
 The chemical shift is generally expressed in parts per million (ppm).
 It is measured by δ scale, τ scale.
 τ = 10 – δ
 Greater the deshielding of protons, larger will be the value of δ
4

5. SCALE OF NMR SPECTRUM
01.02.03.04.05.06.07.08.09.010.0
5
δ
10.09.08.07.06.05.04.03.02.01.00
τ
Highly shielded signals up
field
Deshielded signals downfield

6. FACTORS INFLUENCING CHEMICAL SHIFT:
 Electro negativity effect:
 Chemical shift increases as the electro negativity of the attached
element increases.
Multiple substituent's have a stronger effect than a single
substituent.
• Hybridization effect:
Methine group appear at greater chemical shift than methylene
and methyl
 Methine > methylene > methyl.
• Hydrogen bonding:
Acid hydrogens: least shielded protons are those attached to
carboxylic acids.
Hydrogen bonding and exchangeable hydrogens: they are usually
found attached to a hetero atom.
The more hydrogen bonding that takes place the more deshielded
a proton becomes.
6

7. SPIN-SPIN COUPLING & SPIN SPIN
SPLITTING
• The coupling interaction between two or more protons, most often
through the bonds,result in splitting of the spectral lines. this is
called spin-spin coupling.
 It means that an absorbing peak is split by more than one
“neighbour” proton.
 The spitting is a very essential part to obtain exact information
about the number of the neighbouring protons.
 Chemical equivalent protons do not result in spin-spin splitting.
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8. PASCAL’S TRIANGLE:
 The intensity ratios of multiplets derived from n+1 rule follows the
entries in the mathematical device called pascal’s triangle.
 Each entry in the triangle is the sum of entries above it and to it
immediate left and right.
8

9. (n+1) Rule:
 If a signal is split by non equivalent protons, it split in to n+1 peaks.
9

10. COUPLING CONSTANT(J)
 The distance between the center of the two adjacent peaks in a
multiplet is usually constant and is called the coupling constant.
 It is independent of the external field.
 It is measured in Hertz(Hz) or in cps (cycles per second).
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11. NMR SPECTRUM
A spectrum of absorption of radiation Vs applied magnetic
strength is called as NMR spectrum.
It includes:-
1. Number of signals
2. Their intensity (as measured by area under peak)
3. Splitting pattern (multiplicity)
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12. NUMBER OF SIGNALS
 It shows how many different kinds of protons are present in the
molecule.
COUNTING HYDROGEN ENVIRONMENTS
 One molecule can contain many hydrogen environments.
12
1 x H environments so
1 peaks in NMR
spectrum.

13. C C
CH3
H
H
H3C
13
2 x H environments so 2
peaks in NMR spectrum.
H2
C
C
H2
OH
H3C
4 x H environments so 4
peaks in NMR spectrum.

14. INTENSITY OF PEAKS
 The size or the area of each peak tells the number of protons in each
set number of protons each set.
 Area under an NMR signal α number of protons giving rise to
signal.
 Greater the number of protons → Greater will be the energy
absorbed & greater is the area under the absorption peak.
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15. SPLITTING PATTERN(MULTIPLICITY)
 The splitting of a signal; is due to the different environments of the
absorbing proton i.e., with respect to the nearby proton(proton
attached to the adjacent carbon atom)
15

16. H
|
─C─
|
H
CH3
Funct.Grp.
CH3
Funct.Grp
+ + =
H
|
─C─
|
H
Peak is from Splitting indicates Chemical shift Final structure
a CH2 adjacent CH3 indicates adjacent
functional group

17. 17

18. 1H NMR Absorptions by type of
compound:
Alkanes:
 Alkanes can have three different types of hydrogens (methyl,
methylene, and methyne)
 Methyl > methylene > methyne.
18
Type of proton Chemical shift
R-CH3 0.7–1.3 ppm
R-CH2-R 1.2-1.4 ppm
R3CH 1.4-1.7 ppm

19. Octane:
19
CH3
CH2

20. Alkenes:
20
 Alkenes have two types of hydrogens: vinyl (those attached directly
to the double bond) and allylic hydrogens (those attached to the a
carbon, the carbon atom attached to the double bond).
Type of proton Chemical shift
C=C-H 4.5-6.5 ppm
C=C-C-H3 1.6-2.6 ppm

21. 2-butene:
21
CH3
CH

22. Aromatic compounds:
22
 Aromatic compounds have two type of hydrogens: aromatic ring
hydrogens (benzene ring hydrogen) and benzylic hydrogens(those
attached to an adjacent carbon atom)
Type of protons Chemical shift
Ar-H 6.5-8
Ar-C-H 2.3-2.7

23. Benzene:
23

24. Alkynes:
24
Pentyne:
Type of proton Chemical shift
C≡C-H 1.7-2.7 ppm
C≡C-CH- 1.6-2.6

25. Alkyl halides:
 F > Cl > Br > I
25
Type of proton Chemical shift
H-C-F
4-4.5
H-C-Cl 3-4
H-C-Br 2.5-4
H-C-I 2-4

26. Methyl bromide
26

27. Alcohols:
 Alcohols have two type of hydrogen's: hydroxyl proton and α
hydrogen's.
27
Type of proton Chemical shift
C-OH 0.5-5 ppm
H-C-OH 3.2-3.8 ppm

28. Ethanol:
28
CH2
OH
CH3

29. Ethers:
 The hydrogen's on the carbons attached to the oxygen
are deshielded due to the electro negativity of the
oxygen.
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Type of proton Chemical shift
H-C-OR 3.3-4

30. Propyl ether:
30

31. Amines:
 Two type of hydrogen's are found in amines: those attached to
nitrogen (the hydrogen's of the amino group) and those attached to
the α carbon( the same carbon to which the amino group is
attached)
31
Type of proton Chemical shift
R-N-H 0.5-4.0 ppm
-CH-N- 2.2-2.9 ppm

32. Propyl ether:
32

33. Nitriles:
 The hydrogen's are slightly deshielded by the cyano group.
33
Type of protons Chemical shift
-CH-C≡N 2.1-3.0 ppm

34. Acetonitrile:
34

35. Aldehydes:
Type of proton Chemical shift
R-CHO 9.0-10.00 ppm
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Acetaldehyde:

36. Ketones:
36
Type of Proton Chemical shift
R-CH-C=O
R
2.1-2.4 ppm
Acetone:
CH3

37. Esters:
 Two types of hydrogens are found I esters:- alcohol part & acid part.
2.1-2.5 ppm 3.5-4.8 ppm
ETHYLACETATE:
37
- 2HC-C-O-CH2 -
O

38. Carboxylic acids:
 These have acidic protons, and the α hydrogen.
38
Type of protons Chemical shift
R-COOH 11-12 ppm
-HC-COOH 2.1-2.5 ppm
Acetic acid:

39. REFERENCES
1. Introduction To Spectroscopy, Pavia, 4th Edition, pg.no:127-161.
2. Elementary Organic Spectroscopy, Y.R.Sharma,pg.no:189-192.
3. Organic Spectroscopy, William Kemp, 3rd Edition,Pg.no:102-110.
4. Spectroscopy, B.K.Sharma,638-643.
5. Spectroscopy Of Organic Compounds , P.S. Kalsi,
6th Edition,pg.no:193-196.
6. http//:wwwchem.uwimona.edu.jm/spectra/nmrintro.html
7. www.ebyte.it/library/educards/nmr/EM360Spectra
8. http//:youtube.com/watch1H NMR spectrum IB Chemistry
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