Radicals formed from acetylenes by high energy radiation and hydrogen atom bombardment: an electron spin resonance study

Abstract

A variety of acetylenic compounds, including acetylenedicarboxylic acid, its salts, and its dimethyl ester, propiolic acid and its salt, mono- and di-phenylacetylene, phenylpropiolic acid, propargyl chloride and bromide, and 1,4-dichlorobut-2-yne have been exposed to ⁶⁰Co γ-rays at 77 K, and the radical products at 77 K and during annealing have been studied by e.s.r. spectroscopy. Several of these compounds were also exposed to beams of hydrogen or deuterium atoms and again examined by e.s.r. spectroscopy at 77 K. Radicals thus identified include hydrogen atom addition products, R¹ĊHCR², several of which are thought to be linear at the radical centre, rather than being bent as in the parent vinyl radical. Curiously, dipotassium acetylenedicarboxylate gave, on exposure to γ-rays at 77 K, H₂CĊCO₂^– radicals. On annealing, new radicals were detected which in several instances were probably dimers formed by addition of the parent radicals to neighbouring acetylene monomers. Other radicals identified include HCCĊH₂, H₂CĊPh, HCCĊHCl, and HCCĊHBr.