NMR Nuclear Magnetic Resonance Chapter 13 Proton Nuclear

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 Insulated tube Coils

Proton NMR Spectrum of Cl 3 CH NMR Signal Magnetic Field

Field here less than Ho H Ho

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.

Cl 3 CH NMR signal 437 Hz at 60 x 106 Hz TMS Magnetic Field

Chemical Shift Scale Chemical Shift = = Position of Signal - Position of TMS Spectrometer Frequency 437 Hz - 0 Hz 60 x 106 Hz x 106 = 7. 28 ppm 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 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?

AB Splitting Measure signal from this proton Magnetic Field from this proton can be aligned or opposed to applied field

Spin Combinations - 2 adjacent protons -C-CH 2 H 1: 2: 1

Spin Combinations - 3 Adjacent Protons -C-CH 3 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

NMR Anisaldehyde

NMR diethyl ketone

NMR i-Pr. OH

NMR n-Propyl iodide

Splitting n-Pr. I

Delta = 100 j=10

Delta = 49 J=10

Delta = 25 J=10

Delta=9 J=10

Me. C OEt What is this compound? CH 3 COCH 2 CH 3

What is this compound? C 6 H 5 COCH 3

Ethyl Benzoate What is this compound? C 6 H 5 COOCH 2 CH 3

MRI y Magnetic field changes across sample x