Premium
Preparation and ESR‐Spectroscopical Investigation of Remarkably Persistent Oxoisobenzofuranyl Radicals
Author(s) -
Kruppa Gary,
Hug Paul,
Liégard André,
Rist Guenther,
Nesvadba Petr
Publication year - 1993
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19930760503
Subject(s) - chemistry , radical , homolysis , steric effects , electron paramagnetic resonance , dissociation (chemistry) , enthalpy , toluene , photochemistry , spectroscopy , computational chemistry , organic chemistry , nuclear magnetic resonance , thermodynamics , physics , quantum mechanics
The synthesis of the diastereoisomeric 1,1′‐diaryl‐1,1′‐bi(isobenzofuran)‐3,3′(1 H ,1′ H )‐diones 3a–d starting from the readily available 2‐aroylbenzoic acids 1a–d is described ( Scheme 1 ). Of the colourless dimers 3a–d , only the sterically congested 3a and 3b dissociate at ambient temperature in solution to the deep red free 3‐oxoisobenzofuran‐1‐yl radicals 4a and 4b , respectively. The radicals 4a, b are extremely persistent in the absence of O 2 . The structures of these radicals are confirmed and the coupling constants assigned by ESR and ENDOR spectroscopy and computer simulation of their ESR spectra. The dissociation equilibrium constant at 20° in toluene for 3a is determined to be 1.18 · 10 −5 M . By studying the steady‐state radical concentration as a function of temperature, the enthalpy and entropy changes for the homolytic dissociation of 3a are determined.