Color centers in poly(arylenesulfophthalides) and the ground state of Müller's hydrocarbon molecule

Abstract

Published data on the properties of Miiller's hydrocarbon are analyzed The total energies of several hydrocarbon biradicals with p-phenytene bridges, including Thiele "s, Chichibabin "s, and Mailer's hydrocarbons in the singtet and triplet states were caicu}ated by the AM I and PM3 scmiempiricat quantum-chemical methods. Contrar),. to popular opinion, our calculations revealed that the M/iller's hydrocarbon molecule has a triplet rather than singlet ground state. The results obtained make it possible to explain the limt that quinoid color centers do not l-arm in the course of reduction of poly(terphenylsulfophthatide). The calculated paramelcrs of eieclronic speclra for singiet states of some related biradicals are reported.

Kekulé versus Lewis: When Aromaticity Prevents Electron Pairing and Imposes Polyradical Character

“…As this series of extended p-quinodimethanes has been studied from Heisenberg-Hamiltonian methods (which do not suffer from spin contamination problems), [27] it will be interesting to compare their geometries and excitation energies with the present DFT results. If substituted by four phenyl groups at their terminal ends, these molecules are known as Thiele's, [28] Chichibabin's, [29][30][31][32][33] and Müller's [34,35] hydrocarbons, respectively. The first member of the series, para-quinodimethane or para-xylylene, 1, is expected to adopt a clear quinonic structure.…”

Can a Topological Approach Predict Spin-Symmetry Breaking in Conjugated Hydrocarbons?

“…The first one is the series of para -dimethylene- para -polyphenylenes, p -R 2 C–(C 6 H 4 ) n –CR 2 and related architectures . This family is better known after the name of the chemists who first synthetized derivatives of this type, namely, Thiele ( n = 1), Chichibabin ( n = 2), and Müller ( n = 3). , The appearance of unpaired electrons on terminal CH 2 groups is not surprising here since it maintains the aromaticity of the benzene rings, which would be destroyed by the full electron pairing on double bonds into a paraquinonic configuration. The appearance of instabilities in the series of linear polyacenes was more surprising and has been the matter of ongoing debates, − as briefly recalled in section .…”