CHE202 - Chapter 13

CHE202 - Chapter 13 - Organic Chemistry 6th Edition L G...

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Organic Chemistry , 6 th Edition L. G. Wade, Jr.
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NMR is the most powerful tool available for  organic structure determination. It is used to study a wide variety of nuclei: 1 H 13 C 15 N 19 F 31 P                                                                             => Chapter 13 2
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A nucleus with an odd atomic number or an odd  mass number has a nuclear spin. The spinning charged nucleus generates a  magnetic field. Chapter 13 3 =>
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When placed in an external field, spinning protons  act like bar magnets. Chapter 13 4 =>
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The magnetic fields of  the spinning nuclei  will align either  with   the external field, or  against  the field. A photon with the right  amount of energy can  be absorbed and  cause the spinning  proton to flip.                      => Chapter 13 5
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Energy difference is proportional to  the magnetic field strength. E  =  h ν  =  γ   h  B 0                             2 π Gyromagnetic ratio,  γ , is a constant for each  nucleus (26,753 s -1 gauss -1  for H). In a 14,092 gauss field, a 60 MHz photon is  required to flip a proton. Low energy, radio frequency.             => Chapter 13 6
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If all protons absorbed the same amount of  energy in a given magnetic field, not much  information could be obtained. But protons are surrounded by electrons that  shield them from the external field. Circulating electrons create an induced  magnetic field that opposes the external  magnetic field.                                 => Chapter 13 7
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Magnetic field strength must be increased for a  shielded proton to flip at the same frequency. Chapter 13 8 =>
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Depending on their chemical environment,  protons in a molecule are shielded by different  amounts. Chapter 13 9 =>
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The  number  of signals shows how many different  kinds of protons are present. The  location  of the signals shows how shielded  or deshielded the proton is. The  intensity  of the signal shows the number of  protons of that type. Signal  splitting  shows the number of protons on  adjacent atoms.                  => Chapter 13 10
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Chapter 13 11 =>
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Chapter 13 12 =>
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TMS is added to the sample. Since silicon is less electronegative than 
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This note was uploaded on 10/10/2010 for the course CHE 202 taught by Professor Richard during the Spring '05 term at SUNY Buffalo.

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CHE202 - Chapter 13 - Organic Chemistry 6th Edition L G...

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