Chapter 16, Problem 16.28P

Interpretation Introduction

Interpretation:

The number of expected ${}^{13}\text{C}$ NMR signals for the given molecule are to be given.

Concept introduction:

${}^{13}\text{C}$ NMR provides valuable information about the carbon skeleton. Each signal in the ${}^{13}\text{C}$ NMR equals to the number of distinct carbon atoms in the given unknown. In most of the ${}^{13}\text{C}$ NMR spectra, almost every time, all the signals would appear as singlets. The saturated carbon atoms appear in the range $\text{δ}\text{0-35 ppm}$ if it is a simple alkane fragment. If it is attached to any electronegative element such as halogens or nitrogen, then the range is $\text{δ}\text{25-70 ppm}$. Triple bonded carbon atoms range from $\text{δ}\text{65-85 ppm}$. Alkene carbons range from $\text{δ}\text{105-150 ppm}$. Carbonyl carbon atoms in acids, esters, amides, and anhydrides range from $\text{δ}\text{120-185 ppm}$. Carbonyl carbons in aldehydes and ketones range from $\text{δ}\text{190-220 ppm}$.

In order to determine the number of chemically distinct carbon atoms in a molecule, we can apply the chemical distinction test by substituting an imaginary atom X for each carbon atom. Then we determine the relationship among those structures. If they happen to be constitutional isomers, then the carbon atoms are dinstict. If they happen to be identical, then the carbon atoms are identical.