How To Find The Most Reactive Position In Electrophilic Aromatic Substitution Reactions?

Predict which position of the naphthalene compound below is the most reactive with electrophiles in electrophilic aromatic substitution?

Predict which position of the naphthalene compound below is the most reactive with electrophiles in electrophilic aromatic substitution?

First, we must determine which ring is the most reactive based on the groups attached to it. Benzene ring on the right has an OH group and a CH3 group. Both of these groups are activating, making the benzene ring on the right more reactive. We can eliminate choice A and B.

Next the most activating group directs where the next group goes. Between OH and CH3, OH is more activating according to the ortho/para/meta directing chart. Therefore, OH determines the position of the next group. OH is an ortho/para director but since the para position is taken, the next group would add ortho (carbon next to) to the OH, therefore giving us choice D as the correct answer.