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Proton NMR Spectroscopy

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Proton NMR Spectroscopy The NMR Phenomenon Most nuclei possess an intrinsic angular momentum, P. Any spinning charged particle generates a magnetic field. – PowerPoint PPT presentation

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Title: Proton NMR Spectroscopy


1
Proton NMR Spectroscopy
2
The NMR Phenomenon
  • Most nuclei possess an intrinsic angular
    momentum, P.
  • Any spinning charged particle generates a
    magnetic field.
  • P I(I1)1/2 h/2p
  • where I spin quantum
  • I 0, 1/2, 1, 3/2, 2,

3
Which nuclei have a spin?
  • If mass and atomic are both even, I 0 and
    the nucleus has no spin.
  • e.g. Carbon-12, Oxygen-16
  • For each nucleus with a spin, the of allowed
    spin states can be quantized
  • For a nucleus with I, there are 2I 1 allowed
    spin states.
  • 1H, 13C, 19F, 31P all have I 1/2
  • DE g(h/2p)Bo

4
Spin states split in the presence of B0
5
  • When a nucleus aligned with a magnetic field,
    B0, absorbs radiation frequency (Rf), it can
    change spin orientation to a higher energy spin
    state. By relaxing back to the parallel (1/2)
    spin state, the nucleus is said to be in
    resonance. Hence,
  • NMR

6
Presence of Magnetic Field
7
NMR instruments typically have a constant Rf and
a variable B0. A proton should absorb Rf of 60
MHz in a field of 14,093 Gauss (1.4093 T). Each
unique probe nucleus (1H perhaps) will come into
resonance at a slightly different - and a very
small percentage of - the Rf. All protons come
into resonance between 0 and 12/1,000,000 (0 12
ppm) of the Rf.
8
Energy Difference (?E) Between Two Different Spin
States of a Nucleus With I1/2
9
What Does an NMR Spectrum Tell You?
  • of chemically unique Hs in the molecule of
    signals
  • The types of Hs that are present e.g. aromatic,
    vinyl, aldehyde chemical shift
  • The number of each chemically unique H
    integration
  • The Hs proximity to eachother spin-spin
    splitting

10
How many signals in the Proton NMR Spectrum?
11
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12
Chemical EquivalenceHow many signals in 1H NMR
spectrum?
13
Number of Equivalent Protons
14
Vinyl Protons
15
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16
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20
Typical 1H NMR Scale is 0-10 ppm
21
The d Scale
22
Tetramethylsilane (TMS)
23
Chemical Shift Ranges, ppm
24
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25
Diamagnetic AnisotropyShielding and Deshielding
26
Deshielding in Alkenes
27
Shielding in Alkynes
28
Chemical Shift is Affected by Electron Density
Around Nucleus
29
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30
from chemistry.msu.edu
31
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32
Methyl t-butyl ether (MTBE)
33
Toluene at Higher Field
34
Integral TraceHow many protons give rise to each
signal?
35
Spin-Spin Splitting
36
The Doublet in 1H NMR
37
Hb in 1,1,2-Tribromoethane
38
The Triplet in 1H NMR
39
Ha in 1,1,2-Tribromoethane
40
1,1,2-Tribromoethane
41
The Quartet in 1HMR
42
Predict Splitting
43
1,1-Dichloroethane
44
Methyl Group appears as an Upfield Doublet
45
Methine H Appears as a Downfield Quartet
46
Ethyl benzene
47
Methyl Isopropyl Ketone
48
1-Nitropropane
49
2-Methyl-1-propanol
50
Para Nitrotoluene
51
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53
C-13 NMR Spectroscopy
54
C-13 chemical shifts
55
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56
Coupling in C-13 NMR
57
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58
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59
Butanone - Coupled and Decoupled
60
1,2,2-Trichloropropane1H and 13C NMR Spectra
61
Coupled C-13 NMR Spectrum
62
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