Question

What is a phenoxide ion?

Answer 1

A phenoxide ion is the conjugate base of phenol. It looks like:

https://commons.wikimedia.org/wiki/Category:Phenoxide_ion

Explanation:

According to the Bronsted-Lowry theory of acids and bases, an acid is a molecule that donates `H^+` ions, and a base is a molecule that takes them up again.

Taking the example of

`NH_3 + H_2O -> NH_4^+ + HO^-`

then `NH_3` acts like a base and `H_2O` acts like an acid, based on the Bronsted-Lowry definitions above.

This makes `NH_4^+` into a conjugate acid (because it would, given the chance, give up hydrogen ions) and `HO^-` the conjugate base (since it would now accept hydrogen).

Phenoxide is a conjugate base, which means it is formed from an acid that has given up its hydrogen. This acid is a phenol molecule, which is a benzene ring with a hydroxyl group. The hydrogen of the hydroxyl leaves, and an `O^-` remains, forming the 'oxide ion' part of the phenoxide ion.

'Phenyl' is simply another systematic name for benzene, a ring of `C_6H_6` with delocalised electrons. 'Phenol' is the alcohol form of benzene, because it has an `-OH` or hydroxyl group.