Acetaldehyde: right to roam

Australian and US chemists have re-shaped our understanding of an important photochemical reaction that defies classical transition state theory and proceeds via multiple barrierless ‘roaming’ pathways.

Traditional teaching has it that chemical reactions proceed from reactants to products via a transition state, and must overcome an energy barrier associated with bond breakage in the reactant species. In recent years, a new class of reaction pathway known as roaming has emerged. Roaming reactions do not follow such a clearly defined pathway, and can be thought of as ‘barrierless’. Developing products do not have sufficient translational energy to fully separate, causing the insipient hydrogen atom to ‘roam’ around the formyl radical (CHO) until an abstraction reaction results in the formation of carbon monoxide and hydrogen gas.

Scott Kable, at the University of New South Wales, Australia, and international collaborators, probed the rotational and translational distributions of acetaldehyde photolysis products methane and carbon monoxide to settle the matter. 

This article provides a link to coverage by Chemistry World