Linear Organosilicone Structures with Delocalized O Bonds.
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1997
- Accession Number
- ADA328315
Entities
People
- Josef Michl
Organizations
- University of Colorado Boulder