Question

Carbon NMR spectroscopy produces a spectrum of only carbon-13 nuclei in a sample. The number of carbon signals in the spectrum corresponds to the number of ________in the molecule. In most carbon NMR spectra, the carbon signals appear as singlet peaks .

Answer 1

Answer:

carbons that are in different environments

Explanation:

When molecules are asymmetric every carbon will have its own peak since they are all different and will show up with a different ppm shift.  If the molecule has symmetry the carbons that are symmetrical (in the same environment) will have the same ppm shift and will therefore show up as one peak.  

An example of a molecule with symmetry is isopropanol which has 3 carbons but only two carbon peaks since the two methyl groups are symmetrical.

An example of a molecule with no symmetry is 3-Nitroaniline where the groups coming off of the benzene ring makes each of the 6 carbons be in different environments and there for all 6 carbons will have different ppm shifts.  The result is a carbon NMR that has 6 peaks.

I hope this helps.  Let me know if anything is unclear.