In the naming of phenols, what does "ortho" signify?

In organic chemistry, "ortho" specifically refers to the positioning of substituent groups on a benzene ring relative to one another. When dealing with phenols, which are compounds containing a hydroxyl group (-OH) directly attached to a benzene ring, the term "ortho" indicates that another substituent group is located on an adjacent carbon atom to the carbon bearing the hydroxyl group.

This close proximity of the substituents can significantly influence the chemical properties and reactivity of the phenolic compound. For example, ortho-substituted phenols may experience intramolecular interactions or steric hindrance that could affect reactivity patterns.

In context, the other choices refer to different configurations: "extra group separated by one carbon" describes a para position, which is not correct for ortho; "extra group on the opposite side" indicates a para arrangement as well; and "no extra groups" would imply a simple phenol without any substituents, which does not fit the definition of ortho. Understanding these distinctions is critical for identifying and naming compounds accurately in organic chemistry.