Accession Number : ADA328315

Title :   Linear Organosilicone Structures with Delocalized O Bonds.

Descriptive Note : Final rept. 15 Feb 94-14 Feb 97,

Corporate Author : COLORADO UNIV AT BOULDER DEPT OF CHEMISTRY

Personal Author(s) : Michl, Josef

PDF Url : ADA328315

Report Date : MAY 1997

Pagination or Media Count : 8

Abstract : Results - Highlights: (1) The generally accepted textbook notion of gauche and anti conformer arrangements about each single bond in a linear saturated chain needs to be revised in that a third conformer (ortho) exists within a certain range of lateral substituent sizes. (2) Electronic excitation in linear all-anti permethylated silicon chains is localized in a single SiSi bond if the chain is six silicon atoms long or shorter and delocalized over all SiSi bonds if the chain has seven or more silicon atoms. (3) In a twisted conformer of Si7Me16, excitation is localized, and this conformer interconverts adiabatically with the all-anti conformer. (4) The chains in which excitation is localized exhibit isomerism of a new type, in which the isomers differ by the location of the stretched bond in which the excitation is localized (stretched bond isomerism). Upon thermal activation, the less stable isomers convert adiabatically to the more stable ones. (5) The usual notion that the lowest singlet electronic excitation energy of an oligosilane strongly depends on conformation is incorrect, at least in the case of decamethyltetrasilane. It is the intensity and not the energy that is exquisitely sensitive to conformation. This is due to the presence of an avoided crossing between configurations that go to sigma sigma(*) and sigma pi(*) limits, respectively, at planar geometry.

Descriptors :   *METHYL RADICALS, *ISOMERS, *CHEMICAL BONDS, *ORGANIC COMPOUNDS, *SILICONES, THERMAL PROPERTIES, LINEAR SYSTEMS, STABILITY, ACTIVATION, EXCITATION, ATOMS, SENSITIVITY, SATURATION, ELECTRON ENERGY, GEOMETRIC FORMS, SILICON, CHAINS, PLANAR STRUCTURES, CONFORMITY.

Subject Categories : Organic Chemistry
      Physical Chemistry
      Atomic and Molecular Physics and Spectroscopy

Distribution Statement : APPROVED FOR PUBLIC RELEASE