Which of the following compounds would you expect to show ultraviolet absorptions in the 200 to

step 1 So now we're just going to be looking at the UV region a bit more and compounds that may be acti

Which of the following compounds would you expect to show...

Key Concepts

Chromophores

Chromophores are the specific molecular moieties responsible for the absorption of light and consequent color. In UV/Vis spectroscopy, regions of a molecule that contain conjugated systems or aromatic rings act as chromophores, determining the wavelengths at which light is absorbed.

UV/Visible Spectroscopy

This analytical method involves the absorption of ultraviolet and visible light by molecules, leading to electronic transitions. It is primarily used to study compounds with conjugated systems, unsaturated bonds, and aromatic rings, and the wavelength range from 200 to 400 nm is especially relevant for these types of electronic transitions.

Electronic Transitions

Electronic transitions occur when electrons are promoted from lower energy orbitals to higher energy orbitals upon absorbing light. The nature of the transition (such as ? to ?* or n to ?*) and the energy gap between these orbitals determine the wavelength of light absorbed.

Conjugation

Conjugation involves the delocalization of ?-electrons across alternating single and double bonds. This electron delocalization lowers the energy difference between the molecular orbitals, often resulting in a red shift (absorption at longer wavelengths) of the absorption band into the 200–400 nm region.

Aromaticity

Aromaticity is a special case of conjugation characterized by cyclic, planar molecules with a delocalized ?-electron system following Huckel’s rule. Aromatic compounds typically display strong UV absorptions due to the extensive delocalization of their ?-electrons, often falling within the 200–400 nm range.

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