Chapter 18, Problem 63IP

Interpretation Introduction

Interpretation:  For the given constitutionally isomeric compounds A, B, C and D with the molecular formula ${\text{C}}_8{\text{H}}_{\text{10}}$, Structure of the compound D should be deduced using the given spectral data.

Concept Introduction:

• In the IR spectrum, the signal just above 3000 ${\text{cm}}^{\text{-1}}$ confirms the presence of  aromatic ring
• Aromatic compound also produces a series of signals between 1450 and 1650 ${\text{cm}}^{\text{-1}}$ in the IR spectrum
• In the ${}^{\text{1}}\text{H}\text{NMR}$ spectrum, the signals between 6.5 and 8ppm confirms the aromatic ring. The presence of a multiplet near 7 ppm is one of the best way to verify the aromatic ring
• ${}^{\text{1}}\text{H}\text{NMR}$: 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.
• HDI Calculation:

            $\begin{array}{l}\text{HDI=}\frac{\text{2(C)+2+N-H-X}}{\text{2}}\\ \text{where}\\ \text{C}\text{represent}\text{the}\text{number}\text{of}\text{carbon}\\ \text{N}\text{represent}\text{the}\text{number}\text{of}\text{nitrogen}\\ \text{H}\text{represent}\text{the}\text{number}\text{of}\text{hydrogen}\\ \text{X}\text{represent}\text{the}\text{number}\text{of}\text{halogen}\text{.}\end{array}$