Chapter 15, Problem 15.47P

Interpretation Introduction

Interpretation:

Two IR spectrums are to be matched with two compounds $\text{cyclohepta-1, 3-diene}$ and $\text{3-methylcyclohexa-1, 4-diene}$ where one IR spectrum has an absorption band at ${\text{1648 cm}}^{-1}$ and the other at ${\text{1618 cm}}^{-1}$.

Concept introduction:

IR spectroscopy enables us to identify different functional groups in the molecule.

One of the greatest advantages of IR spectroscopy is that the frequency of a particular type of vibration is typically found within a characteristic range of frequencies, regardless of the functional group with which the vibration is associated. The fact that absorptions by certain vibrations appear with characteristic frequency ranges enables us to use IR spectroscopy to obtain structural information about a molecule. The $\text{C=C}$ absorptions for alkene appears at $\text{~1620}-{\text{1680 cm}}^{-1}$. The absorption frequency of the conjugated $\text{C=C}$ or $\text{C}\equiv \text{C}$ bonds lowers by $\text{20}-40{\text{cm}}^{-1}$.