What is the Difference Between Hydroxyl and Hydroxide?

05/31/2025 • Felipe Moraes

The main difference between hydroxyl and hydroxide lies in their charge and structure:

Hydroxyl:
Hydroxyl is an electrically neutral compound.
It can be found in two forms: as a radical (OH) and as a covalently bound form in organic compounds.
Hydroxyl groups are found in many organic compounds, such as alcohols, carboxylic acids, and sugars.
They can act as nucleophiles, but are less reactive than other nucleophiles.
Hydroxide:
Hydroxide is a negatively charged ion (OH-) consisting of a hydrogen and an oxygen atom held together by a covalent bond.
Hydroxide ions are more reactive than hydroxyl groups.
When in compounds, OH is called "hydroxide" when it's in a compound with a metal, such as calcium hydroxide or aluminum hydroxide.

In summary, hydroxide is a negatively charged ion, while hydroxyl is an electrically neutral compound or group. Hydroxide ions are more reactive than hydroxyl groups.

Comparative Table: Hydroxyl vs Hydroxide

Here is a table comparing the differences between hydroxyl and hydroxide:

Property	Hydroxyl	Hydroxide
Definition	Hydroxyl is a free radical of formula •OH, consisting of an oxygen and hydrogen atom covalently bonded	Hydroxide is a diatomic anion of formula OH-, consisting of an oxygen and hydrogen atom covalently bonded, with a negative electric charge on the oxygen atom
Charge	Neutral	Negative
Formation	Hydroxyl groups can act as nucleophiles and hydroxyl radical is used as a catalyst in organic reactions	Hydroxide ions form salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions
Reactivity	Hydroxyl groups are not highly reactive as other nucleophiles, but they facilitate the formation of strong intramolecular forces called 'hydrogen bonds'	Hydroxide ions are more reactive than hydroxyl groups in a molecule

I hope this table helps clarify the differences between hydroxyl and hydroxide.