Some comments on the development of free radical chemistry

For many years, an introduction to the chemistry of free radicals has formed an essential part of University chemistry curricula and the subject is of wide relevance to both industrial and biological chemistry, yet its development occurred, with surprising rapidity, less than fifty years ago. It is the aim of this article to give a personal recollection of the circumstances which led to the recognition and early development of this branch of chemistry. From the early days of the last century ‘radicals’ had been defined by chemists as ‘groups of atoms which together behave as a single atom’ and organic chemistry had been regarded as the chemistry of ‘compound radicals’. But with the proof that such simple elements as hydrogen, oxygen and nitrogen exist as binary molecules (H 2 , O 2 , N 2 ) and not as atoms, the possible existence at room temperature, in gases or solutions, of free atoms or radicals was deemed to be unlikely by most chemists of a century ago.