Chapter 15, Problem 72IP

Interpretation Introduction

Interpretation:

The given two constitutional isomers has to be compared and the reason for exhibiting five signals foe first compound and exhibiting six signals for second compound has to be given.

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:

$\text{220-150ppm}$   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)