Chapter 22, Problem 22.10P

Interpretation Introduction

(a)

Interpretation:

The explanation as to why $\text{2, 4-pentanedione}$ contains much less enol form in water ($15\%$) than it does in hexane ($\text{92\%}$) is to be stated.

Concept introduction:

Ketone also exists in two forms which are commonly known as keto-enol tautomerism. Tautomers are isomers which differ only in the position of the protons and electrons of the double bond of the electronegative atom in the compound. There is no change in the carbon skeleton of the compound. This phenomenon which involves simple proton transfer in an intramolecular fashion is known as tautomerism.

Interpretation Introduction

(b)

Interpretation:

The explanation as to why $\text{2, 4-pentanedione}$ has a strong UV absorption in hexane solvent (${\lambda }_{\max }=\text{272 nm},\in =\text{12,000}$), but a weaker absorption in water (${\lambda }_{\max }=\text{274 nm},\in =\text{2050}$) is to be stated.

Concept introduction:

In keto-enol tautomerism, the keto-enol forms of a compound are present in equilibrium with each other. Keto and enol forms both are tautomers of each other, they are inter-convertible to each other by the transfer of $\text{α}$- hydrogen. In UV-Visible spectroscopy, more the conjugation present in the compound, absorption of longer wavelength takes place.