Isomers electron configuration

Decarboxylation of sahcyhc acid takes place with slow heating because of the presence of the electronic configuration of the carboxyl group ortho to the hydroxyl group, but does not occur in the other isomers of hydroxyben2oic acid. On rapid heating, sahcyhc acid sublimes because of its low vapor pressure. This property allows commercial separation from the other isomers as a means of purification analogous to distillation. The differences ia the vapor pressures are shown ia Table 4. 

Despite its very simple electronic configuration (Is ) hydrogen can, paradoxically, exist in over 50 different forms most of which have been well characterized. This multiplicity of forms arises firstly from the existence of atomic, molecular and ionized species in the gas phase H, H2, H+, H , H2" ", H3+. .., H11 + secondly, from the existence of three isotopes, jH, jH(D) and jH(T), and correspondingly of D, D2, HD, DT, etc. and, finally, from the existence of nuclear spin isomers for the homonuclear diatomic species. 

Stronlianile, 385 Strontium atomic size, 379 chemistry, 382 electron configuration. 378 heal of vaporization, 305 hydroxide, K,p, 383 ionization energies, 379 occurrence, 385 properties, 381 Structural formula, 31 Structural isomers, 327 Styrene, 345 Sublimation, 176 Substance, 28 pure, 29, 65, 70... 

In addition to the variation in electronic configuration, the geometric details of the coordination sphere and the properties of iron-ligand bonds (different a- or 71-donor strength) also influence the isomer shift as observed for a series of compounds ... 

The traditional interpretation of the isomer shift in Fe Mossbauer spectra is based on the following assumptions (a) the influence of the 3d electron configuration on the IS occurs via the shielding effect of the 3d electrons on the 3s and 4s electrons, (b) the variations in the 3s shell are dominant, and (c) the influence of the 4s shell occurs via the 4s population. 

A correlation of isomer shift, electronic configuration, and calculated -electron densities for a number of ruthenium complexes in analogy to the Walker-Wertheim-Jaccarino diagram for iron compounds has been reported by Clausen et al. [ 127]. Also useful is the correlation between isomer shift and electronegativity as communicated by Clausen et al. [128] for ruthenium trihalides where the isomer shift appears to increase with increasing Mulliken electronegativity. 

Fig. 7.51 Isomer shift versus formal electron configuration of tungsten compounds (from [226]). The triangles are data taken from [230], the circles from [226]...

Fig. 7.78 Linear relation of the quadmpole splitting A q = ( jl)eqQ (1 + j /3)l/2 and the isomer shift b for aurous (a) and auric (b) compounds. Also included is a correlation with the relative change in electron density at the gold nucleus, Ali/r(o)P, as derived from Dirac-Fock atomic structure calculations for several electron configurations of gold. An approximate scale of the EFG (in the principal axes system) is given on the right-hand ordinate (from [341])...

The oxidation state of the central iron ions in the neutral species [FeL], as well as their monocation and dicationic oxidation products, [Fe(L )]+ and [Fe(L )]2+, are amenable to direct measurement by Mossbauer spectroscopy where the isomer shift gives direct information for the dn electron configuration, provided that the coordination number and the nature of the donor atoms are invariant. Frozen acetonitrile solutions of the above 57Fe enriched species have been investigated by this technique (147). 

Figure 9. Isomer shift as a function of electron configuration...

The Mossbauer effect, although not a substitute for other analytical methods such as x-ray diffraction, can be used to obtain several kinds of structural information about solids. In favorable cases, it is possible to obtain rather detailed information about the electronic configuration of atoms and the local symmetry of their sites by measuring the isomer shift and quadrupole splitting. If more than one valence state of a given atom is present, a semiquantitative determination of the amount of each kind is possible. In solid solutions, the amount of local or long range order can be estimated, and in certain defect structures the relation between the active atoms and the defects can be studied. 

Fig. 6 The Huckel MOs of the three isomeric benzoquinodimethanes [8]. The bonding MOs of the ortho- and para-isomers are filled according to the Pauli exclusion principle. The electron configuration of the non-bonding MOs of the metaisomer is dictated by Hund s rule.

Effects of Isomerism Geometrical isomers of coordination compounds can exhibit different values of redox potential, as accounted for, in various cases, by simple djr orbital level splitting diagrams or by MO calculations. The dependence of the relative stability and redox behavior of the geometrical isomers on the electronic configuration of the metal is also... 

There are five possible constitutional isomers of Cyg whose structures possess closed-shell electronic configurations [15, 62]. The two most abundant of these, C2V-C78 and D3-C78 have been studied extensively by CV and OSWV. In the first study carried out at —15°C in PhMe/MeCN, the C2v isomer displays six one-electron reductions, with the sixth one being irreversible. All waves are... 

Cg4 can be any of 24 stable isomers that satisfy the isolated pentagon rule [4, 6] and possess closed-shell electronic configurations [15]. Before successful HPLC separation and characterization of major and some minor isomers was achieved [53, 55, 56], electrochemical studies of Cg4 involved a mixture of its two major isomers, D2(IV) and D2rf (I I), which at the time could only be isolated as a 2 1 mixture [50, 51, 60]. In solvents such as pyridine, PhCN, and DMF/PhMe, the mixture displayed multiple redox waves, making assignment difficult. In the first OSWV study of the separated isomers, D2-Cg4(IV) displayed four one-electron evenly spaced reductions in pyridine (see Table 8 and Fig. 5) [53]. However, the reduction potentials of the isomer reported as 02 (11) in that same study are now believed to correspond to one of the minor isomers of Cg4, the C2 (IV)... 

The acylation is thought to occur as shown in Scheme 3. The ir-allyl intermediate (5) was isolated in 86% yield and characterized by X-ray analysis.13 The NMR spectrum and crystal structure of (5) indicate that only the anti-al y structure is formed no other positional isomers were detected. The iron atom in (5) obtains a closed-shell electron configuration by intramolecular o-donation of a lone pair of electrons from the acyl oxygen atom, which is confirmed by a lowering the acyl CO bond order (vco 1637 cm-1).12 There is no direct evidence for formation of (4) its intermediacy has been suggested primarily based on the endo stereochemistry of the acylation reaction (see below). 

A The color of stained glass 20.1 Electron Configurations 20.8 Isomers... 

Iron atoms in states other than Fe(II) and Fe(III) are rare in biological material, but there is one case where Mossbauer evidence has pointed to an Fe(IV) electronic configuration. Horseradish peroxidase, when it forms peroxide derivatives (Compounds I and II of HRP), displays an isomer shift which is about equal to that obtained with Fe metal (23). A similar observation has also been found on an analogous compound, Japanese Radish Peroxidase (72). There is no evidence for Fe(I) or Fe (IV) states in any other hemoproteins, or in any of the iron-sulfur proteins. 

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