Chapter 15, Problem 80IP

Interpretation Introduction

Interpretation: The reason for the nonequivalence of two methyl groups in DMF to be interpreted.

Concept Introduction:

${}^{\text{1}}\text{H}\text{NMR}$: The ${}^{\text{1}}\text{H}\text{NMR}$ spectrum gives information on the different electronic environment of protons. The number of signal (proton types) generated in ${}^{\text{1}}\text{H}\text{NMR}$ are predicted by performing symmetry operations (rotation or reflection symmetry).

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 (rotation or reflection 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.

Delocalization of lone pairs: when an atom possess a lone pair (unshared electrons) of electrons next to a $\text{π-bond}$, the lone pair undergoes resonance with the $\text{π-bond}$ by changing its hybridization and gets a double (pi-) bond character.

To Identify: The reason for the nonequivalence of two methyl groups in DMF