Chapter 10.17, Problem 25P

(a)

Interpretation Introduction

Interpretation:

Conjugated organic molecules has to be ranked based on decreasing ${\lambda }_{\max }$.

Concept introduction:

Conjugation on${\lambda }_{\max }$:

The wavelength at which the $\pi \to \pi *$ transition occurs increase as the number of conjugation double bond in the compound increase, the ${\lambda }_{\max }$ of a compound can be used to estimate the number of conjugated double bonds in a compound.

HOMO-LUMO:

In a $\pi \to \pi *$ transition an electron is promoted from the HOMO like a highest occupied molecular orbital to the LUMO lowest unoccupied molecular orbital, if molecule has more conjugated double bonds in a compound, the less energy required for the less electronic transition.

Auxochrome:

When the molecule attached to a chromophores group the both ${\lambda }_{\max }$ and intensity of the absorption will be increased. Some example (-OH, -NH₂) groups are auxochromes.  The loan-pair of electrons on oxygen and nitrogen in the compound are interact with the π-electrons cloud of the aromatic ring by delocalization was occurred.

(b)

Interpretation Introduction

Interpretation:

Conjugated organic molecules has to be ranked based on decreasing ${\lambda }_{\max }$.

Concept introduction:

UV/vis spectroscopy:

It is deal with information about various compounds that have conjugated double, the UV light and visible light have jest the right energy to cause an electronic transition in a molecule that is to promote an electron from one molecular orbital to another higher energy.  

Conjugation on ${\lambda }_{\max }$:

The wavelength at which the $\pi \to \pi *$ transition occurs increase as the number of conjugation double bond in the compound increase, the ${\lambda }_{\max }$ of a compound can be used to estimate the number of conjugated double bonds in a compound.

HOMO-LUMO:

In a $\pi \to \pi *$ transition an electron is promoted from the HOMO like  a highest occupied molecular orbital to the LUMO lowest unoccupied molecular orbital, if molecule has more conjugated double bonds in a compound, the less energy required for the less electronic transition.

Auxochrome:

When the molecule attached to a chromophores group the both ${\lambda }_{\max }$ and intensity of the absorption will be increased. Some example (-OH, -NH₂) groups are auxochromes.  The loan-pair of electrons on oxygen and nitrogen in the compound are interact with the π-electrons cloud of the aromatic ring by delocalization was occurred.