Chapter 15, Problem 15.7P

Interpretation Introduction

Interpretation:

${\text{λ}}_{\text{max}}$ for the longest wavelength absorption of $\text{penta-2, 4-dienal}$, ${\text{CH}}_{\text{2}}=\text{CH}-\text{CH}=\text{CH}-\text{CH}=\text{O}$, is to be estimated.

Concept introduction:

The absorption peak position, ${\text{λ}}_{\text{max}}$, in the UV-vis spectrum depends on the extent of conjugation. Molecules that contain only one sigma bond do not absorb in the UV or visible regions; the ${\text{λ}}_{\text{max}}$ is much too small. On the other hand, a molecule that contains at least one $\text{π}$ bond shows a ${\text{λ}}_{\text{max}}$ greater than $\text{300}$ nm. The value of ${\text{λ}}_{\text{max}}$ for the longest wavelength peak in the spectrum increases as the extent of conjugation increases.