Selenium atomic properties

Occurrence, Extraction and Purification—The Allotropy of Selenium—Colloidal Selenium—General Physical Properties of Selenium—Chemical Properties— Applications of Element—Physiological Action—Atomic Woighl—Valency— Constitution of Selenium Molecule—Detection and Estimation of Selenium. 

Ganther and Corcoran 185) have reported the introduction of selenium into SS bonds to produce compounds of the type R-S-Se-S-R. With reduced RNase at pH 2, 2 moles of selenium can be introduced per protein molecule. Other derivatives have differing amounts of selenium. The monomeric derivatives have some properties similar to RNase-A but only a few per cent of the original enzymic activity. The location of the selenium atoms has not been reported. 

A,B-Diheteropentalenes have only limited solubility in water. The hydrogen donor properties of the NH site of pyrrole and the hydrogen acceptor property of the oxygen atom of the furan ring can increase the solubility of the compounds containing these heteroatoms relative to the systems with only sulfur or selenium atoms in their structure. Alkylation at the nitrogen of furo[3,2-6]pyrrole derivatives increases the solubility in ethanol and other organic solvents. 

One of the main properties of selenides is their aptitude for attack by various nucleophilic reagents. Alkyllithiums, which are not reactive with sulfides, have a marked selenophilic character. They form an ate complex on the selenium atom, which immediately decomposes with cleavage of one C-Se bond leading to the more stable carbanionic species. 

Organometallics bearing a selenium-stabilized caibanion - belong to the well-known family of a-heterosubstituted organometallics which have proved particularly useful in organic synthesis over the past 30 years. Although they share similar features with other members of this family, they possess exceptional properties due to the special behavior of the selenium atom. " ... 

The presence of a selenenyl moiety in organic molecules confers on them unique properties 1 12). The selenium atom in selenides is particularly nucleophilic towards, for example, alkyl halides and halogens 1,2) (Scheme 1) it is oxidizable leading... 

The dichalcogenanthrenes and their allies exhibit marked electron-donor properties and form complexes with certain salts and metal carbonyls <62CB2027, 82DOK(266)ll64, 86JCR(S)326>. Tetramethoxyselenanthrene (78), for instance, forms a complex with mercury(II) chloride in which the selenium atoms are both bonded to the mercury atom, which is approximately tetrahedral in its coordination. The heterocyclic system as a result takes up a more sharply bent conformation than it normally adopts in the free state <86JCR(S)326>. 

The good donor properties of the selenium atom account for the greater reactivity of Se-methyl phosphinoselenoate esters compared with that of an analogous sulphur-containing ester, and the ultimate loss of selenium is a result of the better leaving ability of the —Se (X)R group the participation of diphosphorus intermediates is increased and the overall diastereoselectivity of the sequence reduced ... 

Cluster 47 crystallizes in the trigonal space group R3, whereas 48-50 crystallize in tridinic space (PI). Despite the different crystallographic symmetry, all four compounds display very similar structural properties. A closer look at the atomic arrangements helps to put the preference of this prototypic cluster framework down to highly symmetric substructures. A central selenium atom positioned on the... 

Oxocarbon derivatives either totally or partially substituted by phosphorus and selenium atoms or by nitrogenous groups are examples of the so-called pseudo-oxocarbons [4,49]. Sulfur derivatives are also among these compounds, with the nature of the substituent group resulting in substantial electron delocalization, which is an interesting feature in the context of optical materials with nonlinear properties [20]. The most studied pseudo-oxocarbons and their respective oxocarbons are depicted in Figures 5.3-5.6. 

In the various editions of his textbook, and in the publications dealing specifically with his predictions, Mendeleev repeatedly gives the example of calculating the atomic weight of the element selenium, a property which was known at the time and which could thus be used to test the reliability of his method. 

Table 16.2 Some atomic and physical properties of selenium, tellurium and polonium...

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