Disulfide electronic structure

In this work we examine the low energy UV-visible absorption spectrum of the [Fe2 ft - S2) P o- 61148) )2] complex, Figure 1, whose synthesis, structure, and properties have recently been reported. The complex contains a [Fe — S — S - Fe] core and is a structural isomer of the 2-Fe [Fe — ill — 8)2 — Fe ferredoxin. The electronic structure of the disulfide complex is, however, unknown, and can be associated with either an antifer-romagnetically (AF) coupled [Fe d ) - - Fe d )] system, or with a... 

Isonitrile complexes, having a similar electronic structure to carbonyl complexes, can also react with nucleophiles. Amino-substituted carbene complexes can be prepared in this way (Figure 2.6) [109-112]. Complexes of acceptor-substituted isonitriles can undergo 1,3-dipolar cycloaddition reactions with aldehydes, electron-poor olefins [113], isocyanates [114,115], carbon disulfide [115], etc., to yield heterocycloalkylidene complexes (Figure 2.6). 

Disulfides. Relative to the aromatic chromophores in proteins, the CD spectra of disulfides in proteins has received little attention. This is due to a number of reasons. First, the signals from the disulfides are typically weaker than those arising from aromatic groups. Second, the nature of higher energy excited states in disulfides is poorly understood. Third, little data is available on their electronic structure, either from theoretical treatments [114-116] or from experimental studies [117],... 

Fig. 6.14. A qualitative energy-ievel diagram illustrating the changing electronic structure with occupation of metal 3rf-type orbitals along the series of pyrite-structure disulfides from FeSj to Zn.S, (after Vaughan and Tossell, 1983).

Fig. 6.15. The electronic structures of pyrite-type disulfides based on MS-SCF-Xa calculations on clusters (after Harris, 1982 Vaughan and Tossell,...

Assuming covalent bonds, write electronic structures for the molecules GIF (chlorine fluoride), BrFg (bromine trifluofide), SbCl5 (antimony penta chloHde), HgSg (hydrogen disulfide). In which of these molecules are there atoms with electron configurations that are not noble-gas configurations ... 

The molecular and electronic structures of cyclic disulfide cation radicals of 1,2-dithietane 6 and 1,2-dithiete 7, and radical cations of 1,2-dithiolane 2 (2a-c represent stable conformations determined in terms of the symmetry restriction of Cs, Cz, and Czv), with emphasis on the nature of a two-center three-electron (Zc-ie) sulfur-sulfur bond have been examined by ab initio molecular orbital (MO) calculations <1997JMT(418)171>. Unrestricted Hartree-Fock (UHF)/ MIDI-4(d) computations showed that this bond in organodisulfide radical cation 2 is shorter in comparison to 1,2-dithiolane 2 and possesses partial Jt-bond character (structure A), as previously implied by electron spin resonance (ESR) spectroscopy <1982JA2318>, which correlates best with the form as the most favorable conformation of the cation radical 2. Contrary to the repulsive S-S interaction in the parent 1,2-dithiolane arising from the lone pairs of electrons, the hemi-7t-bond formed by one-electron oxidation should stabilize the five-membered ring of 2, or, for example, a similar cation radical of LA 3 which is involved in diverse biochemical reactions. 

The actual electronic structure of (RSSR) is especially interesting. Key feature is a 2o/10 bond between the two sulfur atoms, rendering [RS.. SR]-an even more appropriate and informative notation.55,56 While further details on this three-electron bond will be dealt with in the odd electron bonds section vide infra), the following is of immediate interest. The combined effect of the two bonding o-electrons and the one antibonding a electron affords a formal bond order of 1/2. This, in turn, provides the rationale for the above equilibrium and relative ease of redissociation of the newly formed sulfur-sulfur bond. The same [RS. . SR] species is, incidentally, formed in the reduction of disulfides by hydrated electrons. Thiyl radicals and disulfide radical anions thus are two conjugate forms of the one-electron redox intermediate between thiols and disulfides. 

Write the resonating electronic structures for the nitrate ion, NOs" the nitrite ion NO2" carbon dioxide, CO2 carbon disulfide, CS2 nitrous oxide, N2O. What shapes do these molecules have and what are the expected values of the bond angles Note that there are three valence-bond structures possible for CO2 that give each atom an argononic structure. 

In essence, two of these three electrons form a n bond, on top of the existing (j bond, and the remaining electron is place into an antibonding n orbital. The sulfur-sulfur bond thus assumes a partial 7c-character 1112,113]. As a direct consequence, the rotation becomes restricted and, particularly in cyclic disulfides, molecular structures may flatten. Even the possible formation of cis- and rran -isomers of (MeSSMe) could recently be verified through identification of two distinct vibrational stretching frequencies evaluated from time-resolved resonance Raman spectroscopy measurements. These findings were also supported by corresponding calculations [118, 119, 146]. 

Joseph Riga Is currently a senior staff member at Namur working mainly on molecular solids and polymers using XPS. He obtained his Ph.D. degree from the Facultes Universitaires Notre Dame de la Palx, Namur, Belgium with a thesis on the electronic structure of organic disulfides. 

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