98192-08-6Relevant academic research and scientific papers
Optical resolution and configurational stability of selenoxides stabilized by intramolecular coordination
Shimizu, Toshio,Enomoto, Masao,Taka, Hideo,Kamigata, Nobumasa
, p. 8242 - 8247 (1999)
2-((Dimethylamino)methyl)phenyl alkyl (or aryl) selenoxides, configurationally stabilized by intramolecular coordination of an amino group to the selenium atom, were optically resolved into their enantiomeric isomers by means of high-performance liquid chromatography using an optically active column packed with amylosecarbamate derivative/silica gel. This is the first example of the isolation of optically pure selenoxides without bulky substituents and also the first isolation of optically pure alkyl aryl selenoxides. The absolute configuration of the (-)-isomers could be assigned to be the S-form by comparison of their specific rotations, circular dichroism spectra, and behavior on the optically active column with those of the sulfur analogue, prepared by Andersen's method. Racemization of the optically active selenoxides was accelerated not only in acidic solution but also in basic media. This result indicates there are two different mechanisms for their racemization in acidic and basic media. The stabilization energy of the selenoxides by the intramolecular coordination of an amino group to the selenium atom was estimated to be ca. 3 kcal mol-1 on the basis of variable-temperature 1H NMR measurements.
Radical cations of aromatic selenium compounds: Role of Se···X nonbonding interactions
Singh, Beena G.,Thomas, Elizabeth,Sawant, Shilpa N.,Takahashi, Kohei,Dedachi, Kenchi,Iwaoka, Michio,Priyadarsini, K. Indira
, p. 9259 - 9265 (2013/10/21)
Selenium centered radical cations in aliphatic selenium compounds are stabilized by formation of two-center-three electron (2c-3e) hemi bonds either with nearby heteroatoms forming monomer radicals or with selenium atoms of the parent molecules forming dimer radicals. Such radicals in aromatic selenium compounds would generally be stabilized as monomers by the delocalization of the spin density along the aromatic ring. To test the assumption if aromatic selenides having Se···X nonbonding interactions can show different types of radical cations, we have performed pulse radiolysis studies of three structurally related aromatic selenium compounds and the results have been substantiated with cyclic voltammetry and quantum chemical calculations. The three aromatic selenium compounds have functional groups like -CH 2N(CH3)2 (1), -CH2OH (2), and -CH3 (3) at ortho position to the -SeCH3 moiety. The energy of Se···X nonbonding interactions (Enb) for these compounds is in the order 1 (Se···N) > 2 (Se···O) > 3 (Se···H). Radical cations, 1?+, 2?+ and 3?+ were produced by the one-electron oxidation of 1, 2 and 3 by radiolytically generated ?OH and Br2?- radicals. Results on transient spectra, lifetime, and secondary reactions of 1?+, 2?+, and 3?+ indicated that 1?+ shows a significantly different absorption spectrum, longer lifetime, and less oxidizing power compared to those of 2?+ or 3?+. Quantum chemical calculations suggested that 1?+ is stabilized by the formation of a 2c-3e bond between Se and N atoms, whereas 2 ?+ and 3?+ acquire stability through the delocalization of the spin density on the aromatic ring. These results provide evidence for the first time that stronger nonbonding interactions between Se···N in the ground state, facilitate the formation of stabilized radical cations, which can significantly influence the redox chemistry and the biological activity of aromatic selenium compounds.
