Molecular mechanisms in the pyrolysis of unsaturated chlorinated hydrocarbons

Abstract

Laser-induced pyrolysis of small chlorinated hydrocarbons at temperatures where radical processes are likely to be unimportant has provided clear evidence for direct low-energy molecular reactions between acetylenes and chlorinated acetylenes or ethylenes. High-level ab initio calculations of possible pathways have shown that these reactions proceed via two routes. Direct bimolecular reaction accompanied by HCl elimination leads to diacetylenes or vinylacetylenes, respectively, while carbene molecular adducts, followed by Cl or H migrations to yield three- or four-membered rings and ring-opening, lead to vinylacetylenes or butadienes, respectively. Analogues of these processes are likely to be central to the growth of larger molecules in such systems.