An EPR and theoretical study of radicals formed from tetraalkylsulfamides [(R2N)2SO2]

Abstract

A series of sulfamides has been synthesised and their primary radical cations studied by EPR spectroscopy following γ-radiolysis in low-temperature freon matrices. These species are readily bleached by visible light (>570 nm), to give secondary radicals, the nature of which varies with the sulfamide used. The ¹⁴N hyperfine data show that the SOMO comprises both nitrogen centres and furthermore that the ¹⁴N tensors are parallel. This implies that a distortion of the sulfamide system occurs on ionisation, since the neutral species (at least for sulfamide and its tetramethyl derivative) adopt bisected structures with an appreciable angle between the nitrogen 2p orbitals. MO calculations indicate that the obvious possibility of a twisting of the N-centres through 90° to form regular ‘allylic ’structures is disfavoured energetically over the retention of the basic bisected geometry, and we suggest therefore that it is a ‘bent-bonding ’distortion that operates to render the N-orbital axes parallel, in accord with the EPR data. Additionally, we have studied radicals formed by radiolysis of the pure sulfamides at 77 K, and conclude that much of the radiation chemistry in these pure systems is driven by electron capture events: these are not possible in the freon media which are themselves efficient electron capture materials, and thus remove them from the reaction system.