Final answer:
The sp² hybridized carbon atoms of alkenes and benzene rings have a trigonal planar geometry and absorb ultraviolet light, which is related to the electronic transitions in their molecular orbitals.
Step-by-step explanation:
The sp² hybridized carbon atoms of alkenes and benzene rings are trigonal planar and absorb ultraviolet light. This occurs because the arrangements of the atoms allow for certain regions of electromagnetic radiation to be absorbed based on the electronic transitions between energy levels associated with the molecular orbitals. For example, in benzene, all carbon atoms have sp² hybridization, resulting in a trigonal planar geometry with bond angles of approximately 120°. Due to the unique bonding arrangement, including resonance stabilization, the benzene ring absorbs energy in the form of ultraviolet light, which can be observed using techniques such as UV/Vis spectroscopy.
When ultraviolet light of the appropriate energy is incident upon these molecules, it can be absorbed by the π electrons during electronic transitions. The absorbed energy promotes these electrons to higher energy levels. The specific wavelengths of light that are absorbed are characteristic of the electronic structure of the molecule, providing valuable information for analysis.
UV/Vis spectroscopy is a commonly employed technique to study these electronic transitions. By measuring the absorption of UV or visible light at different wavelengths, researchers can gather information about the electronic structure of compounds, including the presence of double bonds, aromaticity, and conjugation.