What is hydroxyl?

Hydroxyl is a chemical term and essentially describes a group consisting of one oxygen and one hydrogen atom (–OH). Depending on the context, “hydroxyl” can mean different things, but the basis is always this –OH unit.

What is the hydroxyl group (–OH)?

The hydroxyl group is a functional group in chemistry. It determines the properties and reactivity of many compounds.

Typical examples of the hydroxyl group include:

• Alcohols (e.g., ethanol, methanol): contain at least one –OH group
• Sugars: contain many hydroxyl groups and are therefore highly soluble in water
• Polyvinyl alcohol (PVA) and polyvinyl butyral (PVB): contain –OH groups, which are responsible for adhesion and polarity, among other things

Key properties of the hydroxyl group include its strong polarity and its ability to form hydrogen bonds. As a result, a hydroxyl group generally increases a molecule’s water solubility and overall polarity. It is also chemically reactive and often serves as a starting point for further reactions, such as esterification or ether formation.

What is a hydroxyl radical (·OH)?

In addition to referring to the functional group, “hydroxyl” sometimes also refers to the hydroxyl radical.

• It is a particle with an unpaired electron → therefore highly reactive
• plays an important role in atmospheric chemistry, e.g., in the breakdown of air pollutant.
• It also occurs in biological systems and can damage cellular components there if it forms uncontrollably

What is the practical significance of hydroxyl?

In practice, hydroxyl plays an important role in various fields. In organic chemistry, hydroxyl groups help determine whether a compound is classified as an alcohol, a phenol, or a combination of a carboxylic acid and an alcohol. In materials science and polymer chemistry, the hydroxyl content in polymers such as polyvinyl alcohol (PVA) and polyvinyl butyral (PVB) significantly influences the material’s properties, particularly its adhesion to surfaces such as glass, its water absorption, and its mechanical and optical properties. In environmental and atmospheric chemistry, the hydroxyl radical is particularly important; due to its high reactivity, it breaks down pollutants in the air and is therefore often referred to as the “detergent of the atmosphere”.

In general, a hydroxyl group refers to an –OH group consisting of oxygen and hydrogen. As a functional group, it plays a central role in organic chemistry and is found in many important substances, such as alcohols, sugars, and polymers. In the form of the hydroxyl radical (·OH), it also plays an important role in the breakdown of pollutants in the atmosphere.