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Protons in an external magnetic field Energy difference between the spin-states depends on the strength of the magnetic field.
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NMRNuclearMagneticResonance
Chapter 13
Proton Nuclear Spin States
Two states have the same energy in the absence of a magnetic field
MagneticField
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
CoilsInsulated tube
NMRSignal
Proton NMR Spectrum of Cl3CH
Magnetic Field
H
Ho
Field here less than Ho
Electrons shield nucleus from external magnetic field.
HC
Magnetic field
E = H
Energy to change spin state proportional to field strength
E =h
Measure field strength in FREQUENCY units
Cycles/second
Tetramethylsilane
TMSReference compound for NMR spectrum.
NMRsignal
Magnetic Field
Cl3CH
TMS
437 Hzat 60x106 Hz
Chemical Shift =Position of Signal - Position of TMS
Spectrometer Frequencyx106
Units = parts per million = ppm
Chemical Shift Scale
=437 Hz - 0 Hz
60x106Hzx 106 = 7.28 ppm
Typical Chemical Shifts
CR H
CO
C H
CCl H
CBr H
CO H
0.9 - 1.8
2.1 - 2.5
3.1 - 4.1
2.7 - 4.1
3.3 - 3.7
C H
CCH
H
CO
H
HOR
Typical Chemical Shifts
2.3 - 2.8
4.5 - 6.5
6.5 - 8.5
9 - 10
0.5 - 5
10 9 8 7 6 5 4 3 2 1 0
TMSRHC-C-HO
C HXC = CH
H
C H
O
Proton Chemical Shifts
ppm down field from TMS
Area proportional to number of protons
How many lines would you expect in the proton NMR spectrum of this compound?
Br2CHCH3
Measure signal from this proton
Field from this proton can be aligned or opposed to applied field
Magnetic Field
Spin Combinations - 2 adjacent protons
-C-CH2-H
1 : 2 : 1
Spin Combinations - 3 Adjacent Protons
-C-CH3
H
1: 3: 3: 1
Adjacent Protons Lines
123
234
n + 1
What is the name of this compound?
Ethyl Bromide
CH3CO
OCH2CH3
ICH2CH2CH3
What is this compound?
CH3COCH2CH3
C6H5COCH3
What is this compound?
What is this compound?
C6H5COOCH2CH3
y
x
Magneticfield changesacross sample
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