Transcript NMR - The University of Illinois Archives

NMR
Nuclear
Magnetic
Resonance
Chapter 13
Proton Nuclear Spin States
Magnetic
Field
Two states have the same energy
in the absence of a magnetic field
Protons in an external magnetic field
Energy difference between the spin-states
depends on the strength of the magnetic field.
NMR Spectrometer
Superconducting NMR Magnet
NMR Sample Tubes
NMR Probe
Sample goes
in here
Coils
Insulated tube
Proton NMR Spectrum of Cl3CH
NMR
Signal
Magnetic Field
Field here less than Ho
H
Ho
Electrons shield nucleus from
external magnetic field.
C
H
Magnetic field
Energy to change spin state
proportional to field strength
E=H
E =h 
Measure field strength in FREQUENCY
units
Cycles/second
Tetramethylsilane
CH3
CH3 Si CH3
CH3
TMS
Reference compound for NMR spectrum.
Cl3CH
NMR
signal
437 Hz
at 60x106 Hz
TMS
Magnetic Field
Chemical Shift Scale
Chemical Shift =

=
Position of Signal - Position of TMS
x106
Spectrometer Frequency
437 Hz - 0 Hz
60x106Hz
x 106 = 7.28 ppm
Units = parts per million = ppm
Typical Chemical Shifts
R C H
0.9 - 1.8
C H
2.7 - 4.1
O C H
3.3 - 3.7
Br
O
C C H
Cl
C H
2.1 - 2.5
3.1 - 4.1
Typical Chemical Shifts
C H
2.3 - 2.8
O
C H
H
C C
4.5 - 6.5
R O H
H
9 - 10
6.5 - 8.5
0.5 - 5
Proton Chemical Shifts
H
O
O
C H
10
9
X C
C=C
H
C-C-H
RH TMS
H
8
7
6
5
4
3
2
ppm down field from TMS
1
0
Sample NMR Spectrum
Area proportional to number of protons
Number of lines?
How many lines would you
expect in the proton NMR
spectrum of this compound?
Br2CHCH3
AB Splitting
C
C
H
H
Measure signal
from this proton
Magnetic Field
X
Field from this proton
can be aligned or
opposed to applied
field
Spin Combinations - 2 adjacent protons
-C-CH2H
1:2:1
Spin Combinations - 3 Adjacent Protons
-C-CH3
H
1: 3: 3: 1
Adjacent Protons Lines
1
2
3
n+1
2
3
4
What is the name of this compound?
Ethyl Bromide
NMR Ethyl Bromide
NMR Ethyl
Acetate
O
CH3C OCH2CH3
NMR Anisaldehyde
NMR diethyl ketone
NMR i-PrOH
NMR n-Propyl iodide
Splitting n-PrI
ICH2CH2CH3
Delta = 100 j=10
Delta = 49
J=10
Delta = 25
J=10
Delta=9 J=10
MeC
OEt
What is this compound?
CH3COCH2CH3
What is this compound?
C6H5COCH3
Ethyl
Benzoate
What is this compound?
C6H5COOCH2CH3
MRI
y
Magnetic
field changes
across sample
x