“…50 The use of ultrasound has been recommended to improve the efficiency of these reactions. 51 Hofmann elimination from (o-methylbenzyl)trimethylammonium hydroxide (30), induced iodide debromination of o-xylylene dibromides (28), 1,52 and elimination from o-(trimethylsilyl)methylammonium salts (29), triggered by fluoride ion, 53 have been also used to generate oQDM (Scheme 12).…”
Section: 4-elimination Of Rr′-substituted O-xylenesmentioning
confidence: 99%
“…Formation of 80 may be explained as being the result of oQDM having considerable radical character. In a series of experiments, Errede 262 prepared oQDM itself by the flash pyrolysis of o-methylbenzyltrimethylammonium hydroxide (30), the oQDM being quenched soon after it was formed by cooling to -78 °C. The product trapped out under these conditions was an approximately 25:75 mixture of a 1,2,5,6-dibenzocyclooctadiene 80 and the spiro oquinodimethane dimer 299 (Scheme 69).…”
Section: A Polymerization Of Benzocyclobutene Monomers Containing The...mentioning
confidence: 99%
“…Despite the great amount of research focused on the 8π-electron oQDM system, the 9π-electron quinodimethane radical anion and its derivatives have remained elusive. Although resonance-energy calculations suggest that the oQDM radical anion should be well stabilized, it has eluded unequivocal experimental observation. , It has been only recently that the oQDM radical anion of α,α‘-bis(trimethylsilyl)- o -quinodimethane ( 16 ) was prepared by photolysis of a suitable precursor (Scheme ) at −120 °C with a high-pressure mercury lamp (500 W), which leads to a strong ESR signal ( g = 2.0029) showing hyperfine splittings of 0.698 (2H) and 0.192 mT (4H) 5 …”
Section: Structure and Properties Of O-quinodimethanesmentioning
“…50 The use of ultrasound has been recommended to improve the efficiency of these reactions. 51 Hofmann elimination from (o-methylbenzyl)trimethylammonium hydroxide (30), induced iodide debromination of o-xylylene dibromides (28), 1,52 and elimination from o-(trimethylsilyl)methylammonium salts (29), triggered by fluoride ion, 53 have been also used to generate oQDM (Scheme 12).…”
Section: 4-elimination Of Rr′-substituted O-xylenesmentioning
confidence: 99%
“…Formation of 80 may be explained as being the result of oQDM having considerable radical character. In a series of experiments, Errede 262 prepared oQDM itself by the flash pyrolysis of o-methylbenzyltrimethylammonium hydroxide (30), the oQDM being quenched soon after it was formed by cooling to -78 °C. The product trapped out under these conditions was an approximately 25:75 mixture of a 1,2,5,6-dibenzocyclooctadiene 80 and the spiro oquinodimethane dimer 299 (Scheme 69).…”
Section: A Polymerization Of Benzocyclobutene Monomers Containing The...mentioning
confidence: 99%
“…Despite the great amount of research focused on the 8π-electron oQDM system, the 9π-electron quinodimethane radical anion and its derivatives have remained elusive. Although resonance-energy calculations suggest that the oQDM radical anion should be well stabilized, it has eluded unequivocal experimental observation. , It has been only recently that the oQDM radical anion of α,α‘-bis(trimethylsilyl)- o -quinodimethane ( 16 ) was prepared by photolysis of a suitable precursor (Scheme ) at −120 °C with a high-pressure mercury lamp (500 W), which leads to a strong ESR signal ( g = 2.0029) showing hyperfine splittings of 0.698 (2H) and 0.192 mT (4H) 5 …”
Section: Structure and Properties Of O-quinodimethanesmentioning
“…According to REPEs, cyclooctatetraene shows a highly antiaromatic nature (REPE is −0.074 β), but its dianion and dication possess an aromatic nature, with REPE values of 0.019 and 0.031 β, respectively [60,61,69].…”
This review summarizes the results on the aromaticity of a series of synthesized and hypothetical neutral heterocirculene molecules and their double charged ions. The aromaticity of heterocirculenes is a direct reflection of their electronic structure responsible for the specific optoelectronic and photophysical properties. We show how the presence of a heteroatom in the outer macrocycle affects the aromaticity of hetero[8]circulenes. In addition, we also describe the change in aromaticity and strain energy for a series of the “lower” (n < 8) and “higher” (n > 8) hetero[n]circulenes. It was demonstrated that the loss of planarity with increased strain leads to an increased antiaromaticity of the lower hetero[n]circulenes, whereas higher hetero[n]circulenes demonstrate a more pronounced aromatic nature because of the small departure from planarity of each heteroarene ring in hetero[n]circulene molecule. Finally, we discuss the aromatic nature of the first examples of π-extended hetero[8]circulenes.
“…Accordingly, the NICS(0) criteria cannot be used for predicting the aromaticity of these compounds. In general, those monocyclic -electron systems which contain (4n + 2) -electrons, following the Hückel rule, are aromatic; whereas those monocyclic systems containing 4n electrons are strongly antiaromatic; and those monocyclic systems containing either a (4n + 1) or a (4n + 3) number of -electrons are weakly antiaromatic [32,33]. In a polycyclic -electronic system, the contributions of individual circuits to aromaticity obey the Hückel rule [34,35].…”
Section: Global Aromaticity Of the C 24 Isomersmentioning
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