Chapter 15, Problem 15.3P

Interpretation Introduction

Interpretation:

The approximate energy difference between the HOMO and LUMO is to be calculated from the given UV-vis spectrum.

Concept introduction:

The UV-vis spectrum of a is a plot of relative absorbance as a function of the wavelength.

The position of the peak in the spectrum, called ${\text{λ}}_{\max }$, is the wavelength at which the absorbance reaches a local maximum. This is the wavelength of the photon that is absorbed by the active molecule and corresponds to the transition of an electron from its ground state to an empty higher energy orbital.

The transition of an electron from the HOMO to the LUMO requires the least energy of all possible electron transitions on that molecule. This is because an electron in the HOMO has the highest energy of all electrons in the ground state, and the LUMO is the lowest energy empty orbital available. This energy then corresponds to the longest wavelength band (or peak) in the UV-vis spectrum.