Lecture8 - The α and β Spin States • Since the α state...

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Unformatted text preview: The α and β Spin States • Since the α state is lower in energy than the β state, it is more “populated.” The energy difference between these two states is proportional to the applied external magnetic Feld (H ). β α E H Δ E ! = H° " 2 # " = gyromagnetic ratio β α E H Δ E = h ν Resonant Frequency 125.7 11.7 13 C 500 11.7 1 H 282.40 7 19 F 75.47 7 13 C 300.13 7 1 H Resonant Frequenc y (MHz) Magnetic Field Strength (Tesla) Nuclei + – + – + – + – + – + – ! Spin State " Spin State + – EMR # E $ = # E/h Spin Flip + – + – + – + – + – + – ! Spin State " Spin State + – Spin Relaxation X INTENSITY FREQUENCY ( $ ) AT 7 TESLA 300 MHz Signal Observed! + – + – + – + – + – + – ! Spin State " Spin State + – EMR # E $ = # E/h Spin Flip + – + – + – + – + – + – ! Spin State " Spin State + – Spin Relaxation X INTENSITY FREQUENCY ( $ ) AT 7 TESLA 300 MHz Signal Observed! LIGHT ABSORBED! X INTENSITY FREQUENCY ( ! ) AT 7 TESLA 300 MHz Signal Observed! Signal Observed! Nuclei in different electronic environments resonate at slightly different frequencies. The differences between these are in Hertz not Megahertz! For example, different hydrogens or different carbons within the same molecule or in different molecules will appear as unique signals (peaks). Example of a 1 H-NMR Spectrum H 3 C O O CH 3 How many peaks in the 13 C NMR spectrum? 3 Increasing frequency Why are there only two peaks when there are six hydrogens?...
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This note was uploaded on 10/25/2009 for the course CHEM 3AL taught by Professor Li during the Spring '08 term at Berkeley.

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Lecture8 - The α and β Spin States • Since the α state...

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