Chapter 15.12, Problem 9LTS

Interpretation Introduction

Interpretation: The number of signals and the chemical shift range of each signal to be predicted.

Concept Introduction:

The ${}^{\text{13}}\text{C}\text{NMR}$ spectrum gives information on the different electronic environments of carbon. As like ${}^{\text{1}}\text{H}\text{NMR}$, the number of signals generated in ${}^{\text{13}}\text{C}\text{NMR}$ are predicted by performing symmetry operations (rotational or reflectional symmetry). Only chemical shift values are reported in the spectrum but not the multiplicity and integration values because the coupling between two neighboring ${}^{\text{13}}\text{C}{-}^{\text{13}}\text{C}$ nuclei are weakly involved due to the low abundance of ${}^{\text{13}}\text{C}$ isotopes of carbon atom.

Chemical shift range: The bench mark chemical shift region for the carbons of different electronic environments.

$\text{220-150ppm}$ Carbon atoms of carbonyl groups are highly deshielded.

$\begin{array}{l}\text{150-100ppm}\\ \end{array}$    ${\text{sp}}^{\text{2}}$-hybridized carbon atoms.

$\text{100-50ppm}$ $\text{sp}$-hybridized carbon atoms as well as ${\text{sp}}^3$ hybridized carbon atoms that are deshielded by electronegative atoms.

$\text{0-50ppm}$ ${\text{sp}}^3$ hybridized carbon atoms(methyl, methylene and Methine groups)