Nuclear Spin Interactions

1
Nuclear Spin Interactions
NMR Signal A B C D E
Start with out of the magnet.
Energy levels are the same.
E O
D
NMR Signal A
A Zeeman Interaction
2
Nuclear Spin Interactions
NMR Signal A B
A Zeeman Interaction
B Chemical Shift Interaction
CH3
C-OH
3
Nuclear Spin Interactions
NMR Signal A B C D
A Zeeman Interaction
B Chemical Shift Interaction
C J-coupling or spin-spin interaction
D Dipolar Interaction
R
R
Consider
- N - C
- N - C
R
H H
H H
- N - C -
Homonuclear
H..
H coupling
1
1
H H
R
R
- N -
C
- N -
C
13
13
H H
H H
Observed nucleus
Heteronuclear
H..
C coupling
1
13
4
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5
180 y pulse
6
(180) pulses
p
z
z
z
t
p
y
x
x
x
y
y
180 x pulse
7
Spin Echo
t
p
t
8
Heteronuclear Coupled Doublet - On Resonance
a
b
a
b
Carrier frequency
9
Heteronuclear Coupled Doublet - Off Resonance
y
t
x
a
b
a
d
b
y
p
a
b
t
x
x
a
Carrier frequency
d
(slow)
b
(fast)
10
Homonuclear Coupled Doublet - On Resonance
y
t
R
R
x
C
- N -
- N -
C
H H
H H
a
b
p
y
b
b
R
R
t
C
- N -
- N -
C
x
x
H H
H H
b
a
a
a
180 pulse also flips the neighboring
proton. This changes the a and b labels.
11
Homonuclear Coupled Doublet - On Resonance
a
b
large J-coupling
b
a
small J-coupling (spins dephase more slowly)
12
Homonuclear Coupled Doublet - On Resonance
a
b
a
b
y
larger J-coupling
b
a
b
x
large J-coupling
a
b
a
a
b
small J-coupling
Phase of the NMR resonances depends on the value
of t
13
2D J-resolved Spectroscopy
J
0 J
2 J
14
2D J-resolved Spectroscopy
t o
y
y
t
a
x
x
Time 1
b
y
p
a
t
a
x
x
b
b
Frequency 2
15
2D J-resolved Spectroscopy
t o
Time 1
t
Intensity
Frequency 2
16
2D J-resolved Spectroscopy
Frequency 1
J Hz
0
1/2J
J
Frequency 2
17
General One Dimensional Experiment
Acquire
t1
Fourier Transformation resolves multiple
frequencies that overlap in the time domain
Fourier Transform t1 -gt f1
f1
18
General Two Dimensional Experiment
Acquire
t1
t2
Fourier Transform t1 -gt f1 and t2 -gt f2
f1
f2
19
General Two Dimensional Experiment
Acquire
t1
t2
Vary t1 Collect a series of 1D spectra
Acquire
t1
t2
Acquire
t1
t2
20
General Two Dimensional Experiment
t1
Vary t1 Collect a series of 1D spectra
f2
Here, the intensities of and do
not change as a function of the t1 evolution time
21
General Two Dimensional Experiment
t1
Vary t1 Collect a series of 1D spectra
f2
Whereas here, the intensity of is modulated
as a function of the t1 evolution time
22
General Two Dimensional Experiment
t1
Transpose and then Fourier transform in t1
dimension
f2
23
General Two Dimensional Experiment
t1
Transpose and then Fourier transform in t1
dimension
f2
24
General Two Dimensional Experiment
Projection on f2 gives original chemical shifts
f1
f2
25
General Two Dimensional Experiment
Projection on f1 yields new information
f1
f2
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27
Measuring J-Couplings
H
O
Glycine
Simplest Spin System - AX
C
N
C
D
H
J
Phase-sensitive COSY
aH
aH
28
Measuring J-Couplings
H
Alanine
H
C
H
O
Spin System - A3X
C
N
C
D
H
H
C
H
C
H
H
H
CH3
Phase-sensitive COSY
H
C
H
H
H
C
H
aH
H
H
C
H
29
Measuring J-Couplings
Spin System - AMX
Serine
A
OD
bH1
H
C
H
O
C
N
C
M
D
H
bH2
Phase-sensitive COSY
X
aH
30
Measuring J-Couplings
Spin System - AMX
Serine
OD
C
Ha
Hm
O
C
C
N
D
Hx
active coupling
Ha
Hm
C
passive coupling
C
Ha
C
Hm
C
C
Hx
Hx
31
Measuring J-Couplings
H
Alanine
H
C
H
O
Spin System - A3X
C
N
C
D
H
active coupling
CH3
Phase-sensitive COSY
passive coupling
aH
Treat only one H of CH3 as active pair
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34
Heteronuclear Selective Population Transfer
4
4
C
13
3
3
H
2
1
2
H
1
Saturation of
1,3 transition
C
13
1
1
3,4
1,3
1,3
2,4
1,2
2,4
1,2
3,4
H ..................
C
1
13
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37
Carrier between a and b
a on resonance
38
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