Chapter 15, Problem 15.34P

Interpretation Introduction

Interpretation:

Color dependence of the given structures of phenolphthalein under various pH conditions is to be explained.

Concept introduction:

${\lambda }_{\max }$ depends heavily on the extent of conjugation. The value of the longest-wavelength ${\lambda }_{\max }$ increases as the extent of conjugation increases.

If absorption takes place in the UV region, human eyes do not register any wavelength as human eyes are able to detect the absorption only in the visible region.