Electron Spin Resonance of Tetraphenylpyrryl Radical

Abstract

The free radical 2,3,4,5-tetraphenylpyrryl in dilute, oxygen-free solution gives an electron spin resonance rich in hyperfine structure. The principal features of the spectrum are seven peaks in a binomial intensity distribution. These are attributed to approximately equal isotropic hyperfine interactions with the six ortho and para protons of the 2- and 5-phenyl groups. A molecular-orbital computation of spin densities in the pyrryl ring is qualitatively consistent with this result. The radical concentration may be enhanced by ultraviolet radiation but subsequently decays toward its original value with second-order kinetics. It is postulated that: (i) the radical dimerizes spontaneously until an equilibrium between radical and dimer is established; (ii) the dimer may undergo photodissociation back to the radical.

Oxidation and Reduction of the Pyrrole Ring

“…(79,92) The major oxidation pathway leads to the expected products (B43), (B44), and (B45), but 2,3,5,6-tetraphenylpyrazine (B24) is also isolated. (96) Exposure of the radicals to air produces the dipyrrylperoxide (Β48), (3δ) whilst it has been assumed that the radicals, produced in the absence of oxygen, are in equilibrium with the thermochromic and photochromic 1,1-dipyrryl compound (B46). The same compound is obtained from the oxidation of the tetraphenylpyrrole with lead dioxide in chloroform and with perbenzoic acid.…”

Potentiell photochrome brückenkopfsubstituierte Furo[2,3-d]furane

“…(CH), 125.5 (C q ), 125. 400 (9) [M + -2 Keten], 383 (100), 382 (73), 367 (13), 335 (6), 279 (6), 227 (12), 200 (25).…”

“…-MS (EI, 70 eV): m/z (%) = 382 (100) [M + ], 367 (15) [M + -CH 3 ], 339 (6), 236 (7), 191 (4). HRMS: C 25 H 18 O 4 382.1205 gefunden wie berechnet [103] .…”

“…Bei Homolysen entstehen radikalische Produkte, die bei Delokalisierbarkeit des freien Elektrons meist farbig sind. Ein Beispiel hierfür ist die homolytische Bindungsspaltung von Octaphenyl-1,1'-bipyrrolyl (4) zu den stabilen Radikalen 5 bei Bestrahlung mit Licht [6] . Die Entfärbung der Radikale erfolgt thermisch unter Dimerisierung.…”

“…Abb. 49: Gemessene Konzentrationen der Furofurane 183 (n), 184(5), 79(6) und 179 (l) und Ergebnis der Simulation (durchgezogene Linien) in Abhängigkeit von der Zeit während der Thermolyse bei 100 °C.…”