Carbon-13 NMR
Examples of C-13 NMR spectra
Shown here are some examples of C-13 NMR spectra of pure, simple, organic compounds, each having two non-equivalent carbon atoms whose peaks are labeled in red as C1 and C2 corresponding to the numbered carbons in chemical structures overlaid on the spectra. All three of these spectra are fully proton (1H) decoupled. Right below each of the three spectra, the IUPAC name then the common name of the applicable compound is listed. In each of these spectra, the smaller peak at the far right at a chemical shift= 0 ppm is from the internal standard TMS (tetramethylsilane) added in small quantity to the sample. NMR spectra are essentially graphs of signal intensity vs. chemical shift produced by an instrument called an NMR spectrometer. The NMR analyses of these samples were run in the solvent deuterated chloroform (CDCl3) which is chloroform (normally CHCl3) where the hydrogen (H) is a deuterium (2H) atom, commonly symbolized by D.
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| Ethanal or Acetaldehyde | Ethanoic acid or Acetic acid | Ethanol or Ethyl alcohol |
Since all three preceding C-13 spectra are fully proton decoupled, the carbon atoms appear as narrow singlets (single peaks). Note that the carbons in methyl groups (–CH3, indicated as C2 next to peaks) of all three compounds have a chemical shift rather upfield (close to the right) in the spectra not too far from about 20 ppm. The carbon in the methylene group (–CH2–, indicated as C1) in ethanol is brought further downfield to 58 ppm because that carbon is bonded directly to the oxygen in the hydroxyl group (–OH). Note that the carbonyl group (–CO–, indicated as C1) carbons in acetaldehyde and acetic acid are downfield at the left side of the spectrum, the carbonyl region between about 160 and 220 ppm.