Overview of Free Radicals

It is appropriate to speak of reactive oxygen species instead of oxygen free radicals because molecular oxygen (O2) has a radical nature and can even be called a diradical (two unpaired electrons), but it does not have extreme reactivity, due to quantum - mechanical restrictions. Moreover, many of reactive oxygen species are oxygen free radicals and involved in oxidative damage, but others, such as singlet molecular oxygen (O2) and hydrogen peroxide (H2O2) are non-radicals. So, reactive oxygen species is the appropriate term for these extremely reactive molecules but the current term, oxygen free radicals, is still widely used.