1. Nuclear Magnetic Resonance
Yale Chemistry 800 MHz Supercooled Magnet

2. Atomic nuclei in
The absence of
a magnetic field Bo
Atomic nuclei in the presence
of a magnetic field
 spin - with the field
 spin - opposed to the field

3. The Precessing NucleusHo
 spin
 spin Rf
resonance
no resonance

4. The Precessing Nucleus Again
The Continuous Wave Spectrometer
The Fourier Transform Spectrometer

5. Observable Nuclei
Odd At. Wt.; s = ±1/2
Nuclei H C N F P15 ….
Abundance (%)
Odd At. No.; s = ±1
Nuclei 2H N7 …
Unobserved Nuclei
12C O S16…

6. E = h
h = Planck’s constant:1.58x10-37kcal-sec
E = h/2(Bo)
= Gyromagnetic ratio: sensitivity
of nucleus to the magnetic field.
1H = 2.67x104 rad sec-1 gauss-1
Thus: = /2(Bo)
For a proton,
if Bo = 14,092 gauss (1.41 tesla, 1.41 T),
= 60x106 cycles/sec = 60 MHz
and
EN = Nh= cal/mole

7. Rf Field vs. Magnetic Field for a ProtonBo
E = h/2(Bo)
500 MHz
11.74 T
60 MHz
1.41 T
2.35 T
100 MHz

8. Rf Field /Magnetic Field for Some Nuclei
/2 (MHz/T)
Bo (T)
Rf (MHz)
Nuclei 1H
13C
19F
31P 2H
500.00
11.74
42.58
125.74
11.74
10.71
76.78
11.74
6.54
470.54
11.74
40.08
202.51
11.74
17.25

9. Fortunately, all protons are not created equal!
at 1.41 T
60 MHz
60,000,000 Hz
60,000,600 Hz
Me4Si
upfield
shielded
downfield
deshielded }
60 Hz
240 Hz 1 2 3 5 7 8 9 6 4 10
 scale (ppm) }
500 Hz
at 500 MHz
 = (obs - TMS)/inst(MHz) = ( )/60 = 4.00
chemical
shift

10. Where Nuclei Resonate at 11.74T
76.78
12 ppm 2H
12 ppm
1H (TMS)
500.00
RCO2H
CH4
202.51
~380 ppm
31P (H3PO4)
470.54
~220 ppm
19F (CFCl3)
220 ppm
13C
125.74
-SO2F
-CF2-CF2-
CPH2
PX3
RCH3
R2C=O
500 MHz
400
300
200
100

11. Chemical Shifts of Protons

12. The Effect of Electronegativity on Proton Chemical Shifts1 2 3 5 7 8 9 6 4 10 
TMS
CHCl3
=7.26
CH2Cl2
=5.30
CH3Cl
=3.05
CH4
=-0.20 1 2 3 5 7 8 9 6 4 10 
TMS
CHBr3
=6.83
CH2Br2
=4.95
CH3Br
=2.68

13. Chemical Shifts and Integrals
 2.2 1 2 3 5 7 8 9 6 4 10 
TMS
area = 2
area = 3
 4.0
homotopic
protons: chemically
and magnetically
equivalent
enantiotopic protons:
chemically and magnetically equivalent

14. Spin-Spin Splitting  = 1.2 area = 9 “anticipated” spectrum 1 2 3 5 71 2 3 5 7 8 9 6 4 10 
TMS
 = 6.4 area = 1
 = 4.4 area = 1

15. Spin-Spin Splitting 1 2 3 5 7 8 9 6 4 10  TMS  = 1.2 area = 91 2 3 5 7 8 9 6 4 10 
TMS
 = 1.2 area = 9
 = 4.4 area = 1
 = 6.4 area = 1
observed spectrum H H H H
Jcoupling constant = 1.5 Hz
J is a constant
and independent
of field

16. Spin-Spin Splitting  = 6.4 J = 1.5 Hz = 4.4 J = 1.5 Hz 3 4 7 6 5 8 
local
applied
observed
applied
observed H
local
This spectrum is not recorded at ~6 MHz!
and J are not to scale.

17. Multiplicity of Spin-Spin Splitting for s = ±1/2
multiplicity (m) = 2s + 1
# equiv.
neighbors
spin (1/2)
multiplicity
pattern
(a + b)n
symbol 1
singlet (s)
1/2 2
1:1
doublet (d)
2/2 = 1 3
1:2:1
triplet (t)
3/2 4
1:3:3:1
quartet (q)
4/2 = 1 5
1:4:6:4:1
quintet (qt)

18. 1H NMR of Ethyl Bromide (90 MHz)
CH3CH2Br
 = 1.68
area = 3
for H spins




 = 3.43
area = 2
90 Hz/46 pixels
= 3J/12 pixels
: J= 7.83 Hz
for H spins




19. 1H NMR of Isopropanol (90 MHz)
(CH3)2CHOH
6H, d, J = 7.5 Hz
1H septuplet; no coupling to OH
4.25
3.80
( )x90/6 = 7.5 Hz
1H, s

20. Proton Exchange of Isopropanol (90 MHz)
(CH3)2CHOH
+ D2O
(CH3)2CHOD

21. Diastereotopic Protons: 2-Bromobutane
homotopic sets
of protons
pro-R
Diastereotopic protons R
pro-S

22. Diastereotopic Protons: 2-Bromobutane at 90MHz
d1.70 (3H, d)
d1.03 (3H, t)
d1.82 (1H, m)
d1.84 (1H, m)
d4.09 (1H, m (sextet?))

23. 1H NMR of Propionaldehyde: 300 MHz
d9.79 (1H, t, J = 1.4 Hz)
d1.13 (3H, t, J = 7.3 Hz)
Is this pattern at d2.46
a pentuplet given that
there are two different
values for J?
No!

24. 1H NMR of Propionaldehyde: 300 MHz
quartet of doublets
7.3 Hz
d9.79 (1H, t, J = 1.4 Hz)
d1.13 (3H, t, J = 7.3 Hz)

25. 1H NMR of Ethyl Vinyl Ether: 300 MHz
J = 1.9 Hz
3H, t, J = 7.0 Hz
J = 14.4 Hz
J = 6.9 Hz
d3.96 (1H, dd, J = 6.9, 1.9 Hz)
2H, q, J = 7.0 Hz
d4.17 (1H, dd, J = 14.4, 1.9 Hz)
d6.46 (1H, dd, J = 14.4, 6.9 Hz)

26. ABX Coupling in Ethyl Vinyl Ether
d6.46
14.4
6.9
ABX Coupling in Ethyl Vinyl Ether
d4.17
14.4
1.9
d3.96 (1H, dd, J = 6.9, 1.9 Hz)
d4.17 (1H, dd, J = 14.4, 1.9 Hz)
d3.96
1.9
6.9
d6.46 (1H, dd, J = 14.4, 6.9 Hz)
Another example

27. Dependence of J on the Dihedral Angle
The Karplus Equation

28. 1H NMR (400 MHz): cis-4-t-Butylcyclohexanol
triplet of triplets He
3.0
He  4.03, J(Ha) = 3.0 Hz
J(He) = 2.7 Hz
He 4.03, J(Ha) = 3.0 Hz
J(He) = 2.7 Hz
2.7
400 Hz

29. 1H NMR (400 MHz): trans-4-t-Butylcyclohexanol
triplet of triplets Ha
Ha 3.51, J(Ha) = 11.1 Hz
J(He) = 4.3 Hz
11.1
4.3
30.8 Hz

30. Peak Shape as a Function of  vs. J1 2 3 5 7 8 9 6 4 10  
 >> J J 1 2 3 5 7 8 9 6 4 10 
 ~= J 1 2 3 5 7 8 9 6 4 10 
 = 0

31. Magnetic Anisotropy H Bo
Downfield shift for aromatic protons ( )

32. Magnetic Anisotropy R C H Bo
Upfield shift for alkyne protons ( ) Bo

33. 13C Nuclear Magnetic Resonance
13C Chemical Shifts

34. Where’s Waldo?

35. One carbon in 3 molecules of squalene is 13C
What are the odds that two 13C are bonded to one another?
~10,000 to 1

36. 13C NMR Spectrum of Ethyl Bromide at 62.8 MHz
JCH = 151 Hz C1
JCH = 5 Hz
26.6
JCH = 3 Hz
18.3
JCH = 126 Hz C2
TMS
JCH = 118 Hz 10 20 30
ppm ()

37. 13C NMR Spectrum of Ethyl Bromide at 62.8 MHz
TMS
JCH = 118 Hz
JCH = 151 Hz
JCH = 126 Hz
Off resonance decoupling
of the 1H region removes
small C-H coupling.
JCH = 5 Hz
JCH = 3 Hz C1
Broadband decoupling
removes all C-H coupling. C2 30 20 10
26.6
18.3
ppm ()

38. 13C Spectrum of Methyl Salicylate (Broadband Decoupled)

39. 13C Spectrum of Methyl p-Hydroxybenzoate (Broadband Decoupled)

40. The 13C Spectrum of Camphor

41. The End
F. E. Ziegler, 2004