The molecular structures of Thiele's and Chichibabin's hydrocarbons

Montgomery, L. K.; Huffman, John C.; Jurczak, Edward A.; Grendze, M. P.

doi:10.1021/ja00279a056

Cited by 290 publications

(280 citation statements)

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“…28 It is experimentally found that the para-derivative exhibits singlet ground state together with the smaller bondlength alternation (BLA) of the central benzene ring (0.053 Å) as compared to that of the all-carbon analogue, Thiele's hydrocarbon (0.103 Å). 29 This experimental observation evokes the presence of larger contribution of the open-shell resonance structure in the para-quinodimethane framework for this synthesized system. In addition, it is expected that there exists a large charge transfer from the exocyclic SiH 2 region to the central benzene ring in the same manner as in silene.…”

Section: Introductionmentioning

confidence: 61%

Theoretical Study on the Enhancement of the Second Hyperpolarizabilities of Si-, Ge-Disubstituted Quinodimethanes: Synergy Effects of Open-Shell Nature and Intramolecular Charge Transfer

et al. 2015

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We have investigated the second hyperpolarizabilities (γ), that is, the third-order nonlinear optical (NLO) properties at the molecular scale, of the realistic Si-and Gedisubstituted para-and meta-quinodimethanes from the viewpoint of synergy effect of the open-shell singlet nature and the donor (D)−π−donor (D) intramolecular charge transfer (ICT). It has been revealed that the disubstituted para isomers exhibit strong D−π−D nature together with the intermediate open-shell singlet nature, which leads to their significantly enhanced γ values. These results well demonstrate the validity of our recent result of the theoretical model study on para-quinodimethane with point charges, and also present a new design strategy based on the concept of open-shell NLO that the replacement of the radical site of the π-conjugated carbon framework with the heavier main group elements induces both the larger open-shell singlet nature and the D−π−D type strong ICT, both of which synergetically contribute to the further enhancement of the γ values.

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Section: Introductionmentioning

confidence: 61%

Theoretical Study on the Enhancement of the Second Hyperpolarizabilities of Si-, Ge-Disubstituted Quinodimethanes: Synergy Effects of Open-Shell Nature and Intramolecular Charge Transfer

et al. 2015

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“…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.…”

Section: Para-dimethylene Polyphenylenesmentioning

confidence: 99%

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

Trinquier

Malrieu

2014

Chemistry A European J

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Some conjugated alternant hydrocarbons, of singlet ground state according to Ovchinnikov's rule, may exhibit strong polyradical character, despite admitting complete pairing of electrons in bond orbitals between adjacent atoms. Typical organizations of this kind are encountered in polycyclic frames supporting two or more extracyclic methylene groups. Lewis bond pairing would require quinonization of six-membered rings, whereas safeguarding aromaticity proves sufficient to impose ground-state open-shell character, that is, the existence of unpaired electrons, providing the number of benzene rings to be quinonized is larger than two. Several examples built as variations around para-polyphenylene frames are examined through unrestricted DFT (UDFT) calculations, using various methods for spin decontamination of wavefunctions, geometries, and singlet-triplet energy gaps. They all illustrate how it is possible to conceive architectures that can be written with a closed-shell bond pairing, although they exhibit a large number of unpaired electrons. The same analyses also apply to systems in which quinonization would not kill but only reduce the number of unpaired electrons.

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“…This type of competition between two limiting VB mesomers is a recurrent question for rationalizing the electronic properties of diradicals featuring polyphenylene bridges. 72,75,77 In this respect, it has been established that longer polyphenylene-based diradicals will usually present a dominant diradicalar structure, while shorter ones will present a dominant quinoidal structure, with the "turning" point being usually around two of three aryl rings depending on the nature of the terminal radical units. 78 Thus, terminal units X favoring spin delocalization will favor stronger quinoidal weights and maintain such a character over longer poly(1,4-phenylene) bridges.…”

Section: Discussionmentioning

confidence: 99%

Topological Dependence of the Magnetic Exchange Coupling in Arylethynyl-Bridged Organometallic Diradicals Containing [(η²-dppe)(η⁵-C₅Me₅)Fe^III]⁺ Fragments

et al. 2009

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We have investigated the spin distribution and determined the magnetic exchange coupling J(ab) (defined according to the following Hamiltonian: H(spin) = -2J(ab)S(a).S(b)) for three arylethynyl-bridged organoiron(III) diradicals containing [(eta(2)-dppe)(eta(5)-C(5)Me(5))Fe(III)](+) fragments. Considering the distance separating the Fe(III) centers (>or=11 A), remarkably large intramolecular magnetic interactions between unpaired spins were found for two of them. Thus, an antiferromagnetic coupling (J(ab)) of ca. -190 cm(-1) was experimentally determined for the binuclear Fe(III) species featuring a 1,4-diethynylbenzene bridge 1[PF(6)](2), while a ferromagnetic interaction of over +150 cm(-1) was evidenced for its 1,3-substitued analogue 2[PF(6)](2). We also show that a much weaker interaction (0 > J(ab) >or= -1 cm(-1)) takes place in the 4,4'-biphenyl analogue of 1[PF(6)](2) (3[PF(6)](2)), evidencing that insertion of an additional 1,4-phenylene unit in the bridge severely disrupts the magnetic communication in these diradicals. With the help of NMR and density functional theory, the magnetic properties of these compounds were rationalized and compared to those of the corresponding mononuclear Fe(III) relatives 4[PF(6)] and 5[PF(6)]. Finally, it is shown that, for all of these dinuclear Fe(III) complexes, the structural changes between singlet and triplet spin isomers remain very small regarding the carbon-rich bridge. Thus, even for a strongly coupled diradical such as 1[PF(6)](2), a dominant diradicaloid character dominates the valence-bond description of the singlet state unpaired electrons.

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The molecular structures of Thiele's and Chichibabin's hydrocarbons

Cited by 290 publications

References 0 publications

Theoretical Study on the Enhancement of the Second Hyperpolarizabilities of Si-, Ge-Disubstituted Quinodimethanes: Synergy Effects of Open-Shell Nature and Intramolecular Charge Transfer

Theoretical Study on the Enhancement of the Second Hyperpolarizabilities of Si-, Ge-Disubstituted Quinodimethanes: Synergy Effects of Open-Shell Nature and Intramolecular Charge Transfer

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

Topological Dependence of the Magnetic Exchange Coupling in Arylethynyl-Bridged Organometallic Diradicals Containing [(η²-dppe)(η⁵-C₅Me₅)Fe^III]⁺ Fragments

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The molecular structures of Thiele's and Chichibabin's hydrocarbons

Cited by 290 publications

References 0 publications

Theoretical Study on the Enhancement of the Second Hyperpolarizabilities of Si-, Ge-Disubstituted Quinodimethanes: Synergy Effects of Open-Shell Nature and Intramolecular Charge Transfer

Theoretical Study on the Enhancement of the Second Hyperpolarizabilities of Si-, Ge-Disubstituted Quinodimethanes: Synergy Effects of Open-Shell Nature and Intramolecular Charge Transfer

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

Topological Dependence of the Magnetic Exchange Coupling in Arylethynyl-Bridged Organometallic Diradicals Containing [(η2-dppe)(η5-C5Me5)FeIII]+ Fragments

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Topological Dependence of the Magnetic Exchange Coupling in Arylethynyl-Bridged Organometallic Diradicals Containing [(η²-dppe)(η⁵-C₅Me₅)Fe^III]⁺ Fragments