Lecture16CHM233(10)finalnotes

Lecture16CHM233(10)finalnotes - Chapter 14 NMR Spectroscopy...

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Chapter 14 NMR Spectroscopy
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2 Nuclear Magnetic Resonance Spectroscopy NMR is the most powerful tool available to characterize organic molecules by identifying carbon-hydrogen frameworks within molecules. Two common types of NMR spectroscopy: 1 H NMR is used to determine the type and number of H atoms in a molecule; and 13 C NMR is used to determine the type of carbon atoms in a molecule. The source of energy in NMR is radio waves which have long wavelengths, and thus low energy and frequency.
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3 When a charged particle such as a proton spins on its axis, it creates a magnetic field, causing the nucleus to act like a tiny bar magnet. Nuclear Spin
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4 Magnetic Fields in NMR
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Energy and Nuclear Spin In a magnetic field, there are now two energy states for a proton: a lower energy state with the nucleus aligned in the same direction as B 0 , and a higher energy state in which the nucleus aligned against B 0 .
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6 When an external energy source ( h ) that matches the energy difference ( E ) between these two states is applied, energy is absorbed, causing the nucleus to “spin flip” from one orientation to another. Energy and Nuclear Spin
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The energy difference between the two spin states depends on the strength of the magnetic field Energy and Nuclear Spin
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8 a -spin states b -spin states absorb E release E Signals detected by NMR Energy and Nuclear Spin
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The frequency needed for resonance and the applied magnetic field strength are proportionally related: The stronger the magnetic field, the larger the energy difference between the two nuclear spin states, and the higher the needed for resonance. Resonance Frequency
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This note was uploaded on 01/03/2012 for the course CHEM 233 taught by Professor Anamoore during the Fall '10 term at ASU.

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Lecture16CHM233(10)finalnotes - Chapter 14 NMR Spectroscopy...

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