Final answer:
The presence of a lone pair on an activating group like –OH increases the stabilization of a benzene ring due to the delocalization of electrons and resonance stabilization effects, enriching the ring with electrons and enhancing its reactivity.
Step-by-step explanation:
The stabilization of a benzene ring due to the presence of activating groups is attributed to the delocalization of electrons. Specifically, a group like –OH has a lone pair of electrons on the oxygen atom, which can be donated to the aromatic system. This donation of electrons into the benzene ring enhances its reactivity, as illustrated by the resonance structures where the oxygen atom changes its hybridization from sp³ to sp² to allow for resonance. Consequently, the presence of lone pairs on activating groups like –OH makes the benzene ring more electron-rich and therefore more nucleophilic, which increases the stability and reactivity of the ring.
In the context of resonance stabilization, the delocalization of electrons across multiple atoms lowers the potential energy, making the resonance hybrid more stable than any individual contributing structure. When evaluating molecular geometry, lone pairs also affect the three-dimensional shape and stability of a molecule due to their greater spatial requirement and electrostatic repulsions compared to bonding pairs, as seen when placing the lone pair in the equatorial position in SF4 to minimize repulsions.