Spectroscopy Learning Module, Part 3a

Spectroscopy - NMR spectroscopy is the most powerful tool available for organic structure determination It is used to study a wide variety of

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± NMR spectroscopy is the most powerful tool available for organic structure determination. ± It is used to study a wide variety of nuclei with spin quantum numbers ( l ) of ½, including 1 H, 13 C, 15 N, 19 F, and 31 P. ur focus in this lab will be primarily on 1 ±or ± ² Our focus in this lab will be primarily on H, or proton NMR. ± The spinning charged nucleus generates a magnetic field. ± When the sample is placed in an external agnetic field the nuclei respond to that field magnetic field, the nuclei respond to that field. 1
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± The magnetic fields of the spinning nuclei will align either with the external eld, or against the field. field, or against the field. ± A photon with the right amount of energy (radio waves) can be absorbed by e molecule and cause the the molecule and cause the spinning proton to flip to the high energy state. ± When the nucleus relaxes ack to it’s original state back to it s original state, energy is given off, and we measure that energy as our NMR spectrum. 2
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he umber f signals shows how many ± The number of signals shows how many different kinds of protons are present. he cation f the signals shows how ± The location of the signals shows how shielded or deshielded the proton is. he tensity f the signal shows the number ± The intensity of the signal shows the number of protons of that type. ± Signal splitting shows the number of protons on adjacent carbon atoms. 4
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± Protons that are “chemically equivalent” give one signal in the NMR. ± Look for symmetry – if you can group protons with a subscript, they re equivalent are equivalent. ± Example to the right: 2-chloropropane has 2 inds of protons – e kinds of protons the protons on carbons 1 and 3 and the proton on carbon 2.
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This note was uploaded on 07/14/2011 for the course CHM 2211L taught by Professor Davidson during the Summer '08 term at University of Florida.

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Spectroscopy - NMR spectroscopy is the most powerful tool available for organic structure determination It is used to study a wide variety of

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