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 Probe Coils Sample goes in here Insulated tube
Proton NMR Spectrum of Cl3CH NMR Signal Magnetic Field
Electrons shield nucleus from external magnetic field. Magnetic field
Energy to change spin state proportional to field strength E = H E =h Measure field strength in FREQUENCY units Cycles/second
Tetramethylsilane TMS Reference compound for NMR spectrum.
Cl3CH NMR signal 437 Hz at 60x106 Hz TMS Magnetic Field
Chemical Shift Scale Position of Signal - Position of TMS x106 Chemical Shift = Spectrometer Frequency 437 Hz - 0 Hz x 106 = 7.28 ppm = 60x106Hz Units = parts per million = ppm
Typical Chemical Shifts 0.9 - 1.8 2.7 - 4.1 2.1 - 2.5 3.3 - 3.7 3.1 - 4.1
Typical Chemical Shifts 2.3 - 2.8 9 - 10 4.5 - 6.5 0.5 - 5 6.5 - 8.5
Proton Chemical Shifts RH TMS 10 9 8 7 6 5 4 3 2 1 0 ppm down field from TMS
How many lines would you expect in the proton NMR spectrum of this compound?
Field from this proton can be aligned or opposed to applied field Measure signal from this proton 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 1 2 3 2 3 4 • n + 1
What is the name of this compound? • Ethyl Bromide
What is this compound? CH3COCH2CH3
What is this compound? • C6H5COCH3
What is this compound? C6H5COOCH2CH3
Magnetic field changes across sample y x