215-216 HH W10-NMR-III

215-216 HH W10-NMR-III - 215-216 HH W10 Notes - Dr. Masato...

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215-216 HH W10 Notes - Dr. Masato Koreeda Date: January 6, 2010 Topic : _NMR-III (C-13 NMR) _ page 1 of 2. 13 C NMR Spectroscopy (1) 13 C Isotope (I = 1/2; the same as 1 H) Natural abundance of 13 C is only 1% [99% of carbon is 12 C (I = 0)]. For example, for CH 3 CH 2 OH: A probability of finding 13 C in the CH 3 is 0.01 (1%) and a probability of finding 13 C in the CH 2 is 0.01 (1%). Thus, a probability of finding 13 C in both the CH 3 and CH 2 at the same time is 0.001 (1% of 1%). Therefore, the contribution of 13 C- 13 C coupling in natural abundance 13 C NMR may be ignored. However, 13 C found at any 1 H-attached carbon exhibits spin-spin coupling with the 1 H(s) (one-bond coupling; 1 J 13C,1H ). In order to avoid complications due to these 13 C- 1 H couplings, 13 C NMR spectra are usually obtained by eliminating these couplings by irradiating the entire 1 H NMR absorption range (called decoupling). Consequently, all 13 C NMR peaks are observed as singlets . This mode of obtaining 13 C NMR spectra is called a proton-decoupled
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This note was uploaded on 02/24/2010 for the course CHEM 215 taught by Professor Koreeda during the Spring '07 term at University of Michigan.

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215-216 HH W10-NMR-III - 215-216 HH W10 Notes - Dr. Masato...

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