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 Coils Sample goes in here Insulated tube

Proton NMR Spectrum of Cl3CH Signal Magnetic Field

Field here less than Ho H Ho

Electrons shield nucleus from external magnetic field.

Energy to change spin state proportional to field strength 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 = 60x106Hz x106 437 Hz - 0 Hz x 106 = 7.28 ppm 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

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?

Measure signal from this proton AB Splitting 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

NMR Ethyl Bromide

NMR Ethyl Acetate

NMR Anisaldehyde

NMR diethyl ketone

NMR i-PrOH

NMR n-Propyl iodide

Splitting n-PrI

Delta = 100 j=10

Delta = 49 J=10

Delta = 25 J=10

Delta=9 J=10

MeCOEt What is this compound? CH3COCH2CH3

What is this compound? C6H5COCH3

What is this compound? Ethyl Benzoate C6H5COOCH2CH3

MRI y Magnetic field changes across sample x