what is the hydroxyl group ?

Fundamental Definition

The hydroxyl group (-OH) is a functional group composed of one oxygen atom covalently bonded to one hydrogen atom. As one of the most prevalent functional groups in chemistry, it serves as the defining characteristic of two major compound classes:

• Alcohols: Where -OH binds to sp³ hybridized carbon

• Phenols: Where -OH attaches to aromatic rings

Key Chemical Properties

Electronic Structure

• Polar covalent bond (O-H bond dipole moment: ~1.51 D) • Oxygen's electronegativity (3.44) creates partial charges: δ⁻ on O, δ⁺ on H • sp³ hybridized oxygen with two lone electron pairs

Reactivity Characteristics

• Hydrogen bonding capability (donor and acceptor) • pKa range: ~15-18 (alcohols), ~10 (phenols) • Nucleophilic substitution reactions • Oxidation susceptibility (to carbonyl compounds)

Industrial and Biological Significance

 Material Science Applications

• Polyols in polymer production (polyurethanes, polyesters) • Surface modification through hydroxylation • Solvent formulations (methanol, ethanol, glycols)

 Biochemical Roles

• Carbohydrate structure (sugar -OH groups) • Protein post-translational modifications • Membrane lipid hydrophilic heads

Analytical Identification

Common characterization methods include:

• Infrared spectroscopy (broad ~3200-3600 cm⁻¹ stretch)

• NMR (chemical shift: 1-5 ppm for alcohols)

• Chemical tests (Lucas test, chromic acid oxidation)