Über sterisch gehinderte freie Radikale, XIII. Über das Wittig‐Radikal 4‐Benzoyltriphenylmethyl und analoge mono‐4‐substituierte Tritylradikale

Abstract

Wirtig und Mitarbb. 3) trugen 1932 zur Entwicklung des Vinylogie-bzw. Phenylogie-Prinzips und dariiber hinaus zur Entstehung der Mesomerielehre4) bei, als sie das Titelradikal 1 erstmalig darstellten und mit den damals verfugbaren Mitteln seine Mesomerie studierten. Sie stellten sein chemisches Verhalten dem des kurz vorher von Ltrwenbein und Mitarb. beschriebenen Benzoyldiphenylmethyls (2) gegeniiber (in heutiger Schreibweise). la l b 2aAus der ,,tiefroten" Losung ,,schied sich das Radikal bei langerem Stehen in dunkelroten Prismen ab". Wenngleich auch ,,das in Losung befindliche Dimere ebenfalls" erwahnt wird, so schlossen die Autoren doch offensichtlich zumindest auf einen hohen Dissoziationsgrad3). uber diesen ist nichts weiter bekannt, desgleichen uber die Art des Dimeren.

4-Ferrocenylphenyl-Substituted Tritylium Dyes with Open and Interlinked C+Ar2Entities: Redox Behavior, Electrochromism, and a Quantitative Study of the Dimerization of Their Neutral Radicals

“…The extent of dimerization and the associated equilibrium constants K diss range from 29% ( K diss = 0.67 M) or 57% ( K diss = 0.14 M) in the cases of 3,5-di- tert -butyl- or the 3,5-bis­(adamantyl)-substituted trityl radicals to 97% in the case of the 1-diphenylmethylene-4-triphenylmethyl-2,5-cyclohexadiene-derived radical ( K diss = 3.09 10 –4 M), whereas 2,6-dimethylphenyl­(ethanes) dissociate only with difficulty . While most of these monomer/dimer equilibria were studied by employing electronic absorption spectroscopy or quantum chemical calculations, , Zarkadis et al used EPR spectroscopy to determine the extent of formation of Jacobsen–Nauta-type dimers from trityl radicals Ph 2 C • (C 6 H 4 -R-4) to 17% (R = t Bu) or 18% (R = CF 3 ), respectively . Sakamaki et al highlighted the reversible nature of radical dimerization in hexaphenylethane-type structures (e.g., 9-phenylfluorenyl radicals) ,, in their recent review on dynamic covalent chemistry …”

“…76 While most of these monomer/dimer equilibria were studied by employing electronic absorption spectroscopy or quantum chemical calculations, 74,75 Zarkadis et al used EPR spectroscopy to determine the extent of formation of Jacobsen−Nautatype dimers from trityl radicals Ph 2 C • (C 6 H 4 -R-4) to 17% (R = t Bu) or 18% (R = CF 3 ), respectively. 77 Sakamaki et al highlighted the reversible nature of radical dimerization in hexaphenylethane-type structures (e.g., 9-phenylfluorenyl radicals) 36,38,78 in their recent review on dynamic covalent chemistry. 79 Unfortunately, all of our attempts to crystallize any of the reduced complexes have failed so far.…”

Superacid-Catalyzed Reaction of Substituted Benzaldehydes with Benzene

“…Data for 15 : colorless powder; 1 H NMR δ 7.80 (d, 2H, 7.0 Hz), 7.74 (d, 2 H, 8.4 Hz), 7.57 (t, 1 H, 7.5 Hz), 7.46 (t, 2 H, 8.2 Hz), 7.31 (t, 4 H, 7.3 Hz). 7.2−7.3 (m, 4 H), 7.13 (d, 4 H, 7.0 Hz), 5.63 (s, 1 H).…”

Photochemistry and Photophysics of (p-Benzoylphenyl)diphenylmethyl and (p-Benzoylphenyl)bis(4-tert-butylphenyl)methyl Radicals in Different Solvents

“…The equilibrium concentrations of 1 and 5 can be calculated on the basis of the dimerization equilibrium constant, , K = 308 M -1 , and [ 1 ] 0 ([ 1 ] 0 = [ 4 ] assuming quantitative conversion of the starting chloride 4 ; negative Beilstein test). Thus, one can plot [ 1 ] eq /[ 5 ] eq as a function [ 1 ] 0 in benzene (Figure )…”