Benzopinacol Radical Cation

Abstract

The absorption spectrum of the elusive benzopinacol radical cation is presented for the first time. This species could be characterized spectroscopically in an argon and organic matrixes. On the basis of experimental results and density functional calculations the structure of the benzopinacol radical cation has been identified as that of a stable complex between two interacting moieties.

Benzophenone Absorption and Diffusion in Poly(dimethylsiloxane) and Its Role in Graft Photo-polymerization for Surface Modification

“…If on the other hand triplet BP relaxes by hydrogen abstraction and BP ketyl radicals are formed, a weak photoluminescence signal can be detected in the green wavelength range (∼550 nm). This photoluminescence signal is in the wavelength range of the first electronic transition of the BP ketyl radical (545 nm , ), while the second electronic transition at about 332 nm is still close enough to be excited at a low yield by the used UV light . The observed photoluminescence might therefore either be phosphorescence of the BP ketyl radicals themselves or of the reaction production of the ketyl radicals, “isobenzopinacol”, an unstable intermediary toward the final arrangement of the stable benzopinacol, with chromophores close to those of the ketyl radicals themselves.…”

“…This photoluminescence signal is in the wavelength range of the first electronic transition of the BP ketyl radical (545 nm 33,71 ), while the second electronic transition at about 332 nm 71 is still close enough to be excited at a low yield by the used UV light. 72 The observed photoluminescence might therefore either be phosphorescence of the BP ketyl radicals themselves or of the reaction production of the ketyl radicals, "isobenzopinacol", an unstable intermediary toward the final arrangement of the stable benzopinacol, 73 with chromophores close to those of the ketyl radicals themselves. The appearance of such isobenzopinacol intermediates (In) toward the formation of stable benzopinacol on longer time scales is well-known in the literature.…”

“…54 Absorption at this additional peak diminishes over time, as the end product benzopinacol has no significant absorption in this wavelength range (see Figure 8a). However, cleavage of benzopinacol can be easily induced 72 even by UV exposure at long wavelengths above the intrinsic absorption, which produces BP ketyl radicals and In 74 and yields again phosphorescence at this particularly large red-shift in the green wavelength range. 75 This UV-induced benzopinacol cleavage and subsequent phosphorescence of In was demonstrated on the microscope on dry benzopinacol crystals (Figure 7b).…”

Anthralin: Primary Products of Its Redox Reactions

“…This finding led us to expect that reduction of the anthralin dimer, (2) 2 , will lead to its spontaneous cleavage. Such so-called mesolytic fragmentation processes are more commonly activated by removal of an electron, thus providing a useful method of breaking bonds that are quite strong in neutral substrates, , but there are also some examples of fragmentations following attachment of an electron . According to DFT calculations, mesolytic fragmentation of the radical anion of (2) 2 to 2 - and 2 • is exothermic by 5.7 kcal/mol in the gas phase (and probably more so in MTHF because of stronger solvation of the more localized monomer anion).…”