Question

on your own words explain reaction and influence in the UV-vis spectrum

how does benzonphenone affects the spectrum of ethanol and why? (benzonphenone in ethanol)

how does benzonphenone affects the spectrum of cyclohexane and why? (benzonphenone in ethanol)

how does benzonphenone affects the spectrum of n-hexane and why? (benzonphenone in n-hexane )

how does benzonphenone affects the spectrum of methylene chloride and why? (benzonphenone in methylene chloride)

Answer 1

Influence of solvents on UV spectrum of benzophenone can be explained by first explaining the structure of benzophenone. The benzophenone molecule consists of two benzene rings and one carbonyl in between them. The carbonyl group is stabilized by resonance with the phenyl groups on each side.

In ethanol benzophenone can form H-bonds with the solvent molecule. The oxygen of the benzophenone interacts with the ethanol molecule thereby causing the lambda max of ethanol to shift. Also benzophenone peaks would shift towards higher wavelenght values due to this H-bonding between the solute and the solvent. Please note ethanol is a polar protic solvent.

The spectrum will have almost no effect when in cyclohexane which is a non-polar solvent in type.

In n-hexane, which is a non-polar solvent, does not interacts with the benzophenone molecule. The spectra would thus have no effect.

In methylene chloride, a solvent which is a polar aprotic in nature. The charge separation on the C=O bond of the benzophenone are enhanced in this solvent. thus, the UV spectrum will have a higher wavelength shift.