Which parts of the molecule benzophenone are chromophores?
is it the two aromatic rings?
what types of electronic transitions are responsible for the molecule absorbing the light?
To determine which parts of the molecule benzophenone are chromophores, we need to examine its structure.
Benzophenone consists of a central carbonyl (C=O) group, flanked by two aromatic rings. In terms of chromophores, the aromatic rings are the key components.
A chromophore is a part of a molecule that can absorb certain wavelengths of light, promoting electrons to higher energy levels. In benzophenone, the two aromatic rings (phenyl groups) are conjugated with the carbonyl group, creating an extended π-electron system.
Conjugation refers to the alternating pattern of single and double bonds, which allows the π-electrons to be delocalized across the entire conjugated system. In benzophenone, the conjugation occurs between the carbonyl group and the benzene rings, resulting in an extended area of electron density that can absorb light.
Regarding the types of electronic transitions responsible for the molecule's light absorption, they are typically π→π* transitions. When benzophenone absorbs light, one of its π-electrons is promoted from a lower-energy π-orbital (filled) to a higher-energy π*-orbital (unoccupied). This promotion of electrons is responsible for the absorption of light in the ultraviolet (UV) region of the electromagnetic spectrum.
In summary, the two aromatic rings (phenyl groups) in benzophenone are the chromophores, and the molecule undergoes π→π* electronic transitions to absorb light.