Free radical

A is an atom, molecule, or ion that has unpaired valence electrons.With some exceptions, these unpaired electrons make free radicals highly chemically reactive towards other substances, or even towards themselves: their molecules will often spontaneously dimerize or polymerize if they come in contact with each other. Most radicals are reasonably stable only at very low concentrations in inert media or in a vacuum.

Molecule that contains at least one unpaired electron. Most molecules contain even numbers of electrons, and the covalent chemical bonds holding the atoms together within a molecule normally consist of pairs of electrons jointly shared by the atoms linked by the bond. Most radicals may be considered to have arisen by cleavage of normal electron-pair bonds, every cleavage having produced two separate entities, each of which contains a single, unpaired electron from the broken bond .


Properties of free radicals

The free radicals are unique and rare species. Free radicals are present only under special and limited conditions. Free radicals are highly reactive and very unstable can donate an electron or accept an electron from other molecules. Free radicals can behave as oxidants or reactants.

The free radial species like nitrogen monoxide and nitrogen dioxide are stable. The molecular oxygen is a free radical, it is a bi radical species. The standard and stable molecular oxygen is in triplet state and the two unpaired electrons have the same spin orientation in two orbitals respectively, having the same orbital energy based on Hund’s rule.

Following are the important free radical that is consists of oxygen(hydroxyl radical)


Nitric oxide radical

Superoxide anion radical

Hydrogen peroxide

Peroxyntrite radical

Types of free radicals

The most of organic radicals are quite unstable and very reactive. The types free radicals are as follows:

1. The neutral radicals

2. The charged radicals

Sources of free radicals

Free radicals are generated internally through sources like Mitochondria, Inflammation, Exercise, Phagocytosis and Peroxisomes

Free radicals are found externally in sources like Environmental pollution, Vehicle & cigarette smoke, Radiation, Drugs & pesticides and Ozone layer