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Relevant bibliographies by topics / Three centre-four electron

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Journal articles

Academic literature on the topic 'Three centre-four electron'

Author: Grafiati

Published: 4 June 2021

Last updated: 16 February 2022

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Journal articles on the topic "Three centre-four electron"

1

Karafiloglou, Padeleimon, and Richard D. Harcourt. "Aspects of three-electron two-centre, four-electron three-centre and six-electron five-centre bonding in cycloimmonium ylides." Journal of Molecular Structure: THEOCHEM 729, no. 3 (2005): 155–61. http://dx.doi.org/10.1016/j.theochem.2005.03.019.

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2

Harcourt, Richard D. "Increased Valence or Electronic Hypervalence for Symmetrical Three-Centre Molecular Orbital Configurations." Australian Journal of Chemistry 60, no. 9 (2007): 691. http://dx.doi.org/10.1071/ch07189.

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With ψ1 = y + k1a + b, ψ2 = y – b, and ψ3 = y – k3a + b as Y–A and A–B bonding, non-bonding, and antibonding three-centre molecular orbitals for a symmetrical Y–A–B type bonding unit with overlapping atomic orbitals y, a, and b, it is deduced that the maximum value for the A atom valence, (VA = Vab + Vay), is (a) 4(3 – 2√2) = 0.6863 for the one-electron and five-electron configurations Φ(1) = (ψ1)1 and Φ(5) = (ψ1)2ψ2)2(ψ3)1; (b) 8(3 – 2√2) = 1.3726 for the two-electron and four-electron configurations Φ(2) = (ψ1)2 and Φ(4) = (ψ1)2(ψ2)2; and (c) 4/3 for the three-electron configuration Φ(3) = (ψ1)2(ψ2)1. Thus for each of the three-centre molecular orbital configurations, the A-atom can exhibit increased valence, or electronic hypervalence, relative to the valence for an A-atom in a two-centre molecular orbital configuration. When k1 ≠ 0 for Φ(1) and k3 ≠ 0 for Φ(5), the A-atom odd-electron charge is not equal to zero. This odd-electron charge is available for (fractional) electron-pair bonding to a fourth atom X, to give an additional contribution, Va, to the valence. The resulting maximum value for the A-atom valence (VA = Vab + Vay + Va) is equal to 1.2020 for each of Φ(1) and Φ(5). A-atom valencies are calculated for the three-centre bonding units for several molecules and ions. The expressions for VA = Vab + Vay were derived with atomic orbital overlap integrals omitted. The present paper shows how the theory is modified when these integrals are included.

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3

Aschenbach, Lara K., Fergus R. Knight, Rebecca A. M. Randall, et al. "Onset of three-centre, four-electron bonding in peri-substituted acenaphthenes: A structural and computational investigation." Dalton Trans. 41, no. 11 (2012): 3141–53. http://dx.doi.org/10.1039/c1dt11697e.

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4

Mayer, I. "Bond orders in three-centre bonds: an analytical investigation into the electronic structure of diborane and the three-centre four-electron bonds of hypervalent sulphur." Journal of Molecular Structure: THEOCHEM 186 (April 1989): 43–52. http://dx.doi.org/10.1016/0166-1280(89)87037-x.

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5

Knight, Fergus R., Kasun S. Athukorala Arachchige, Rebecca A. M. Randall, Michael Bühl, Alexandra M. Z. Slawin, and J. Derek Woollins. "Exploring hypervalency and three-centre, four-electron bonding interactions: Reactions of acenaphthene chalcogen donors and dihalogen acceptors." Dalton Transactions 41, no. 11 (2012): 3154. http://dx.doi.org/10.1039/c2dt12031c.

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6

Baird, N. Colin, Markus Kuhn, and Toyanne M. Lauriston. "On the prediction of the structures of simple and hypervalent hydrides and fluorides containing unpaired electrons." Canadian Journal of Chemistry 67, no. 11 (1989): 1952–58. http://dx.doi.org/10.1139/v89-304.

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Abinitio molecular orbital calculations are reported for the optimum structures of many free radicals, including several species in which the central atom is hypervalent, and for some triplet states. Most geometries are close to those predicted by the VSEPR method for molecules with one additional electron, with the unpaired electron occupying a "lone pair" position. Deviations from the ideal geometries of hypervalent radicals can be rationalized in terms of different strengths for repulsions between electrons of different types. Alternatively the geometries can be understood by using the three-centre, four-electron bond theory for the hypervalent species and the σ-conjugation concept for the non-hypervalent molecules. The distortions from ideality of the hypervalent structure occur to allow interaction of the electron pair of the nonbonding MO of the three-center unit to interact with a lobe of the unpaired electron's orbital. Keywords: geometry of free radicals, abinitio MO theory for radicals, VSEPR theory for radicals, sigma conjugation for radicals.

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7

Segawa, Hiroshi, Akio Nakamoto та Takeo Shimidzu. "Photoinduced axial bond exchange reaction of dichlorophosphorus(V)tetraphenylporphyrin chloride: photochemical activation of central three-centre four-electron bond through the σ–π interaction". J. Chem. Soc., Chem. Commun., № 15 (1992): 1066–67. http://dx.doi.org/10.1039/c39920001066.

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8

Diamond, Louise M., Alexandra M. Z. Slawin та J. Derek Woollins. "Crystal structure of 2-phenyl-2λ4,3-ditelluratetracyclo[5.5.2.04,13.010,14]tetradeca-1(12),4,6,10,13-pentaen-2-ylium trifluoromethanesulfonate". Acta Crystallographica Section E Structure Reports Online 70, № 9 (2014): o1003—o1004. http://dx.doi.org/10.1107/s1600536814018170.

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In the title compound, C18H13Te2+·CF3O3S−, the TeIIatom of the cation and one O atom of the trifluoromethanesulfonate counter-ion form a close-to-linear Te—Te—O system, with a Te—Te—O angle of 172.3 (1)° and a Te—O distance of 2.816 (5) Å, which may suggest the presence of a three-centre–four-electron (3c–4e) bond. Secondary Te...O interactions [3.003 (4) and 3.016 (4) Å], involving the second TeIIatom of the binuclear molecule, are also noted, resulting in a supramolecular layer in thebcplane.

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9

Xiao, Zhiguang, and Anthony G. Wedd. "Metallo-oxidase Enzymes: Design of their Active Sites." Australian Journal of Chemistry 64, no. 3 (2011): 231. http://dx.doi.org/10.1071/ch10428.

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Multi-copper oxidases are a large family of enzymes prevalent in all three domains of life. They couple the one-electron oxidation of substrate to the four-electron reduction of dioxygen to water and feature at least four Cu atoms, traditionally divided into three sites: T1, T2, and (binuclear) T3. The T1 site catalyzes substrate oxidation while a trinuclear cluster (comprising combined T2 and T3 centres) catalyzes the reduction of dioxygen. Substrate oxidation at the T1 Cu site occurs via an outer-sphere mechanism and consequently substrate specificities are determined primarily by the nature of a substrate docking/oxidation (SDO) site associated with the T1 Cu centre. Many of these enzymes ‘moonlight’, i.e. display broad specificities towards many different substrates and may have multiple cellular functions. A sub-set are robust catalysts for the oxidation of low-valent transition metal ions such as FeII, CuI, and MnII and are termed ‘metallo-oxidases’. They play essential roles in nutrient metal uptake and homeostasis, with the ferroxidase ceruloplasmin being a prominent member. Their SDO sites are tailored to facilitate specific binding and facile oxidation of these low-valent metal ions and this is the focus of this review.

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10

Kayar, S. R., H. Hoppeler, B. Essen-Gustavsson, and K. Schwerzmann. "The similarity of mitochondrial distribution in equine skeletal muscles of differing oxidative capacity." Journal of Experimental Biology 137, no. 1 (1988): 253–63. http://dx.doi.org/10.1242/jeb.137.1.253.

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A morphometric analysis was performed on horse muscle tissue to quantify mitochondrial distribution relative to capillaries. Samples of M. vastus medialis, M. semitendinosus, M. masseter and M. cutaneus thoracicus were preserved in a glutaraldehyde fixative for electron microscopy, or frozen for biochemical and histochemical analysis. These four muscles varied from highly oxidative in type, consisting nearly completely of type I fibres, in masseter, to highly glycolytic, primarily type IIb fibres, in cutaneus. In all four muscles, mitochondria were found in highest volume density near capillaries at the fibre border, with a sharp decline in volume density towards the fibre centre. This distribution was independent of myoglobin concentration, muscle fibre type and the activities of three key metabolic enzymes, citrate synthase, 3-OH-acyl-CoA dehydrogenase and lactate dehydrogenase.

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