Ch_322a_9.014

Ch_322a_9.014 - magnetically different carbons are in the...

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Carbon-13 NMR (CMR) Spectroscopy The carbon-13 nucleus ( 13 C), like 1 H, has a nuclear spin quantum number of 1/2. However, this isotope occurs in a natural abundance of only 1.1% . The major isotope of carbon, 12 C, is not "nmr active" since it has a nuclear spin quantum number of I =0. 6 6 1 However, commercial instruments have been available for more than 20 years that allow the recording of quality cmr spectra using the naturally occurring minor isotope of carbon. The low level of 13 C simplifies the cmr spectra.
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Some Key Points about CMR Spectroscopy (1) The number of resonances is a measure of how many
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Unformatted text preview: magnetically different carbons are in the structure. (2) The splitting of a resonance indicates how many hydrogens are attached to that carbon. (The splittings may be eliminated by running proton-decoupled spectra. See below.) (3) The chemical shift reflects the hybridization of the carbon: sp 3 , sp 2 , sp. (4) The chemical shift is also affected by the electronic environment of the carbon (inductive influences) and other shielding and deshielding effects. (5) Note: the signal intensities in cmr spectroscopy are not related to the relative numbers of the carbons....
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This note was uploaded on 07/22/2009 for the course CHEM 322AL taught by Professor Jung during the Summer '07 term at USC.

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Ch_322a_9.014 - magnetically different carbons are in the...

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