Activating Substituents in Aromatic Compounds

Aromatic compounds are a vital class of organic molecules characterized by their stability and unique structural features. They are defined by the presence of a conjugated pi-electron system and exhibit resonance. One of the most recognized aromatic compounds is benzene, which consists of six carbon atoms arranged in a hexagonal ring, with alternating double bonds. The stability and reactivity of aromatic compounds arise largely from their delocalized electrons.

When considering substitutions on the benzene ring, it is critical to recognize the impact of different substituents. For example, some groups are considered activating, while others are deactivating, based on their electronic effects. Understanding these effects is essential for predicting the outcomes of electrophilic aromatic substitution reactions.

Which of the following substituents is considered an activating group for the benzene ring, promoting reaction with electrophiles?