Photochemical Formation of Free Radicals from Olefinic and Acetylenic Compounds in the Frozen State as Studied by Electron Spin Resonance¹

Interpretation of electron spin resonance evidence for the mechanism of free-radical-induced reactions of methylenecyclobutane and methylenecyclopentane

“…We have shown that such a spectrum results from incomplete resolution with coupling constants of 18 and 14 G assigned to the CH2 and CH protons. 6 From the absorption spectrum constructed on this basis, the theoretical peak intensities are 1:2.3: 2.3:1. (It may be noted that well resolved spectra of allenyl radical have been obtained in fluid media by Fessenden and Schuler,4 acm = 18.9 G and och -12.6 G, and by Kochi and Krasin7 Och, = 18.9 G and och = 12.7 G).…”

Electron Paramagnetic Resonance

“…Interestingly, in the aryl ethynyl radical the unpaired electron is rather localized, whereas in the aliphatic radical the electron delocalizes over the triple bond. In another study of several acetylenic radicals (348) it has been noted that the acetylenic form, HC=C-CH2, of a radical is more stable than the allenic form, HC=C= CH2.…”

Decarboxylative 1,4-carbocyanation of 1,3-enynes to access tetra-substituted allenes via copper/photoredox dual catalysis

“… 11 When the functionalizations of 1,3-enynes are concerned, there are a number of key challenges to be addressed. The allenyl radicals generated are short-lived, 12 whereas allenes are excellent radical acceptors. 1 a ,13 Controlling regioselectivity of the reaction is another challenge.…”