Question

Why are phenols acidic in nature?

Answer 1

Hint: Phenoxide ion is stable in nature which is formed when phenols lose its hydrogen atom. This means phenols become stable on losing hydrogen atoms.

Complete step by step answer:
Phenols are compounds that contain hydroxyl groups directly attached to an aromatic carbocyclic nucleus. Phenols react with active metals such as potassium, sodium and form phenoxide. These reactions indicate phenols are acidic in nature. Reactivity of phenols is higher than alcohols because phenols react with aqueous sodium hydroxide to produce phenoxide ion. Phenol is acidic in nature because it can lose hydrogen ions from its $OH$ bond, as on losing this hydrogen phenoxide ion is formed which is stable. Though it is a weak acid it is in equilibrium with the phenolate anion ${C_6}{H_5}{O^ - }$ which is also called phenoxide. Phenol is more acidic than aliphatic compounds containing $OH$ group due to resonance stabilization of phenoxide ion by the aromatic ring. In this way negative charge of oxygen atom is delocalized on ortho and para carbon atoms. Due to which stability increases. Carbon atom adjacent to a group present on a benzene ring is called ortho carbon. There are two ortho carbons in an aromatic compound. Carbon atom adjacent to ortho carbon is called meta carbon. Meta carbons are also two in an aromatic compound. Carbon atom opposite the group present on the benzene ring is para carbon. Para carbon is only one in a ring. Phenoxide ion is a strong nucleophile with nucleophilicity comparable to the one of the carbanions or tertiary amines. It can react with both its oxygen and carbon sites as an ambident nucleophile. Ambident nucleophiles are nucleophiles having two nucleophilic sites. Therefore an ambident nucleophile has two sites through which they can attack.

Note: Due to delocalization of charge phenoxide ion is stable in nature. Also phenoxide ion is an ambident nucleophile.