Nuclear Magnetic Resonance Spectroscopy

Nuclear Magnetic Resonance Spectroscopy

History
1940‘s first evidence for NMR signals (1945)
1950‘s explanation of the influence on the chemical
environment on the shift of NMR signals
1952 Noble prize for Bloch/Purcell for developing
NMR spectroscopy
1960‘s improvement of sensitivity by multiple
measurements and Fuorier-Transformation
evaluation
1970‘s improvement of resolution by application of
supraconducting magnets yielding in higher field
strengths
1980‘s development of multidimensional methods
1990‘s development of pulsed field gradient methods
2000‘s Coupling of NMR with chromatographic methods
development of even higher fields of the magnets

N
-
+
p
p
n
+
-
S
Particle
Charge
Spin
Magnetic Moment
(relative)
Gyromagnetic
constant γ
10 -7 rad T -1 s -1
Proton
+1
½
+1.6
26.8
Neutron
0
½
-1
-18.3
Electron
-1
½
-1060
-17608

102
No
-
101
Md
-
100
Fm
-
99
Es
-
98
Cf
-
97
Bk
-
96
Cm
-
95
Am
-
94
Pu
-
93
Np
-
92
U
-
91
Pa
-
90
Th
-
89
Ac
-
*
*
**Actinoids
70
173 Yb
14.3
69
169 T
m
100
68
Er
-
67
Ho
-
66
Dy
-
65
Tb
-
64
Gd
-
63
Eu
-
62
Sm
-
61
Pm
-
60
Nd
-
59
Pr
-
58
Ce
-
57
La
-
*
*Lanthanoids
118
Uuo
-
117
Uus
-
116
Uuh
-
115
Uup
-
114
Uuq
-
113
Uut
-
112
Uub
-
111
Rg
-
110
Ds
-
109
Mt
-
108
Hs
-
107
Bh
-
106
Sg
-
105
Db
-
104
Rf
-
103
Lr
-
*
*
88
Ra
-
87
Fr
-
7
86
Rn
-
85
At
-
84
Po
-
83
Bi
-
82
207 Pb
22.6
81
205 Tl
70.5
80
Hg
-
79
Au
-
78
195 Pt
33.8
77
Ir
-
76
187 Os
1.6
75
Re
-
74
183 W
14.4
73
Ta
-
72
Hf
-
71
Lu
-
*
56
Ba
-
55
Cs
-
6
54
129 Xe
26.4
53
I
-
52
125 Te
7.0
51
Sb
-
50
119 Sn
8.6
49
In
-
48
111 Cd
12.8
47
107 Ag
51.8
46
Pd
-
45
103 Rh
100
44
Ru
-
43
Tc
-
42
Mo
-
41
Nb
-
40
Zr
-
39
89 Y
100
38
Sr
-
37
Rb
-
5
36
Kr
-
35
Br
-
34
Se
-
33
As
-
32
Ge
31
Ga
-
30
Zn
-
29
Cu
-
28
Ni
-
27
Co
-
26
57 Fe
2.2
25
Mn
-
24
Cr
-
23
V
-
22
Ti
-
21
Sc
-
20
Ca
-
19
K
-
4
18
Ar
-
17
Cl
-
16
S
-
15
31 P
100
14
29 Si
4.7
13
Al
-
12
Mg
-
11
Na
-
3
10
Ne
-
9
19 F
100
8
O
-
7
15 N
0.3
6
13 C
1.1
5
B
-
4
Be
-
3
Li
-
2
2
He
-
1
1 H
100
1
Period
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Group
The number below the element symbol shows the natural abundance of the isotope with I=1/2 in %

Energy
Magn. field strength

Energy
Magn. field strength
Magn. field strength
Energyabsorption
Energyabsorption
Energyabsorption

Energy
Frequency ν
Energy
Energy
absorption
Frequency ν
Energy
Energyabsorption
Magn. field strength
Energyabsorption

1 frequency at once
5 frequencies at once
1.5
1
0.5
0
0 1 2 3 4 5 6 7
-0.5
-1
-1.5
10
8
6
4
2
0
0
-2
1 2 3 4 5 6 7
-4
-6
-8
-10
100 frequencies at once
250 frequencies at once
80
70
60
50
40
30
20
10
0
0
-10
1 2 3 4 5 6 7
-20
-30
100
80
60
40
20
0
0 1 2 3 4 5 6 7
-20
-40

Energy differencies in NMR spectroscopy (intensity of signals)
Magnetic Energy
∆E = h ν = ħ γ B ≈ 4 10 -25 J
Thermal Energy
E = k T ≈ 4 10 -21 J
∆E
m=½
∆E = h ν
B
n m=½
-
n m=-½
=e
∆E
k T
≈ 0.9999
m=-½

Comparison of energies in spectroscopy
Electromagnetic Wave length Frequency Properties to be examined Spectroscopic method
irradiation
γ rays 100 pm – 1 pm 3 10 18 – 3 10 20 Hz Change of nuclear states γ-Spectroscopy, Mößbauer-
Spectroscopy
x-rays 10 nm – 100 pm 3 10 16 – 3 10 18 Hz Change of state of inner electron x-ray Spectroscopy
core state
UV light, visible light 1 µm – 10 nm 3 10 14 – 3 10 16 Hz Change of state of avlence UV Spectroscopy
electrons
Infrared rays 100 µm – 1 µm 3 10 12 – 3 10 14 Hz Change of vibrational
IR/Raman Spectroscopy
states
Microwaves 1 cm – 100 µm 30 GHz – 3 10 12 Hz Change of rotational
Microwave Spectroscopy
states
Microwaves 1m – 1 cm 300 MHz – 30 GHz Change of electron spin Electron spin resonance (ESR)
states
Radiowaves 100 m – 1 m 3 MHz – 300 MHz Change of nuclear spin
states
Nuclear spin resonance (NMR)

IR spectroscopy
13
C-NMR

N
B
B'
M
S
emitter
coil
receiver
coil M=0
N
B'
M
S
rotating angle is
dependent of
irradiation time and
irradiation power
receiver
coil M>0
N
B'
M
S
emitter
coil
emitter
coil

Line broadening (relaxation)
A. spin-lattice relaxation T 1 :
receiver
static magnetic field
transmitter
B z
receiver
T 1
B y
transmitter
static magnetic field
B z
receiver
B. spin-spin relaxation T 2 :
transmitter
B z
B z
T 2
B z
∆E ∆t ≥ ħ
B y
B y

Molecular
vibration
Dynamic
Process
Chemical
exchange processes
Molecular
Rotation
Macroscopic
transport processes
slow
s ms µs ns ps fs
fast
Spectroscopic
Finding
slow
exchange
Longitudinal
Magnetization exchange
Line wideperturbation
fast
exchange
The NMR time scale
Relaxation
time scale
Spectral
time scale
Larmortime
scale

Resonance
frequency
ν Α,Ref.
bare nucleus A
nucleus A
with electron density
e
nucleus A
with more electron densitiy
δ
e
chemical
shift
ν Β,Ref.
bare nucleus B nucleus B
with electron density
e
δ
nucleus B
with more electron density
e

Position of the signal (chemical shift)
δ = ν obs - ν ref
ν ref

Factors influencing the chemical shift (ring current)
δ ≈ 7.2 ppm

Spectrum:
ν 0 ν 1 ν 1
β(β)
H
β
β
β(α)
C
O
H
ν 0 ν 1
ν 1
ν 1
α
α
α(β)
α(α)
bare nucleus
chemical
shift
of electronic
environment
chemical
shift
additionally by
spin environment

Fine structure of the signal (indirect scalar spin-spin coupling)

Spectrum:
ν 0
ν 1 ν 2 ν 1 ν 2 ν 1a/b ν 2a/b
β
β(β)
β(α)
β@β
β@α
β(β)
β@β
H
Cl
β
β
β(α)
β@α
C
N
H
ν
ν 2b
ν 2
ν 2 ν
0 ν 1 ν 1b
1 ν 2a
ν 2 ν 1 ν 1a
α
α
α(β)
α(α)
α@β
α@α
bare nucleus
α
chemical
shift
of electronic
environment
α(β)
α(α)
chemical
shift
additionally by
spin environment
α@β
α@α
additionally active
coupling between
spins

Fine structure of the signal (indirect scalar spin-spin coupling)

1
J-coupling M─X:
Factors influencing the coupling constant
•Oxidation number of M: the higher the Ox-number of M the smaller 1 J MX
•trans-Ligand to M─X: the stronger the trans-influence of the trans-Ligand to M─X the smaller 1 J MX
•Hybridisation of X: the larger the s-amount in the bonding orbital the larger 1 J MX
•Coordination number: the larger the coordination number the smaller 1 J MX
•Gyromagnetic constant: The larger γ M
and γ X
the larger 1 J MX
2
J-coupling X─M─Y:
trans-coupling > cis-coupling
p sp 3 sp 2 sp
90° 109° 120° 180°
1 J RhP =140.7 Hz
2 J PP c=19.8 Hz
2 J PP c=57.5 Hz
Ph Ph
P
O
Rh
O
P
Ph
Ph
P
O
1 J RhP =168.4 Hz
2 J PP c=19.8 Hz
2 J PP t=340.9 Hz
2 J-coupling constant increases
1 J RhP =170.4 Hz
2 J PP c=57.5 Hz
2 J PP t=340.9 Hz
3
J-coupling X─A─B─Y:
φ HCOP =60°
3
J HP =0 Hz
X φ
Y
1 J PPt =2627.5 Hz
φ HCOP =25°
3 J HP =8 Hz
3 J XY = A cos (2 φ) + B cos (φ) + C
1 J PPt =4267.2 Hz
Minimum for φ=60°
Maximum for φ between 0-30° bzw. 150-180°

Information content of a 1D NMR spectrum
Line width of the signal:
life time of the spin state
in the specific environment
Intensity of the signal:
amount of nuclei with
specific environment
Fine structure of the signal:
neighboring nuclear spins
Position of the signal:
electronic environment of the nucleus

Fine structure of the signal (decoupling)
F
F
As
F
Me
Me

Fine structure of the signal (indirect scalar spin-spin coupling)

Fine structure of the signal (indirect scalar spin-spin coupling)

Fine structure of the signal (natural abundance)

Line broadening (Chemical exchange)

Hidden Coordination Sites (Jahn-Teller-Effect)
E
D 4h
C 2v
D 3h
L
L
L
L
M
L
-L
L
M
L
M
L
L
L
High T
31
P-NMR
Low T
a
b

line braodening (exchange decoupling)
13
C-NMR
(3)
(2)
(1)
(3): after addition of much CO
(2): after addition of some CO
(1): starting situation (without additional CO)

Solid state NMR spectroscopy