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On the Role of the π-Contribution to Reverse Polarization for Structure and Stability of Heavy group 14-16 Alkene, Imine, and Carbonyl analogs
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Biochemistry and Organic Chemistry.
In: Journal of the American Chemical SocietyArticle in journal (Refereed) Submitted
URN: urn:nbn:se:uu:diva-97585OAI: oai:DiVA.org:uu-97585DiVA: diva2:172585
Available from: 2008-10-03 Created: 2008-10-03Bibliographically approved
In thesis
1. Lowcoordinated Silicon and Hypercoordinated Carbon: Structure and Stability of Silicon Analogs of Alkenes and Carbon Analogs of Silicates
Open this publication in new window or tab >>Lowcoordinated Silicon and Hypercoordinated Carbon: Structure and Stability of Silicon Analogs of Alkenes and Carbon Analogs of Silicates
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum chemical studies on lowcoordinated group 14-16 compounds have been performed. This thesis focuses particularly on silenes influenced by reverse Siδ-=Cδ+ bond polarization. Hypercoordinated carbon compounds are also studied.

The geometries from calculations with several common computationally inexpensive methods have been tested against high level CCSD/cc-pVTZ geometries for a series of substituted silenes. Hybrid HF/DFT methods performed best among the inexpensive methods tested for silenes.

Heavy alkenes strongly influenced by reverse polarization are found to have less exothermic dimerization energies for both head-to-head and head-to-tail dimerizations, and to have higher activation energies for water addition than naturally polarized heavy alkenes.

We also investigated solvated lithium, magnesium and potassium silenolates and found that lithium and magnesium ions coordinate preferably to O, giving their SiC bond some double bond character.

Reverse polarized 2-siloxy-, 2-thiosiloxy-, and 2-(N-sila-N-methyl)-silenes could according to calculations be formed thermolytically from the corresponding tetrasilanes as transient species. It was, however, found that silenes highly influenced by π-conjugative reverse polarization have low barriers for the back-reaction, and thus these silenes are more difficult to form as stable species than naturally polarized silenes.

It is also found that conjugated 1-siladienes, formed by electrocyclic ring-opening of 1-silacyclobut-2-enes, which are highly influenced by π-conjugative reverse polarization, have higher barriers for electrocyclization back to starting material than naturally polarized 1-siladienes.

It is found that CHe54+, CHe64+, CNe54+, and CNe64+ are the closest carbon analogs of SiH5-, SiH62-, SiF5- and SiF62-, respectively. However, due to their exothermic dissociation reaction, these very high-lying local minima will be impossible to reach experimentally.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 85 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 557
silenes, zwitterionic silenes, silenolates, reverse polarization, natural resonance theory, hypervalent carbon, hypercoordinated carbon, thermolysis, lowcoordinated silicon
National Category
Organic Chemistry
urn:nbn:se:uu:diva-9298 (URN)978-91-554-7294-8 (ISBN)
Public defence
2008-10-25, C8:301, BMC, Husargatan 3 753 21, Uppsala, 10:15 (English)
Available from: 2008-10-03 Created: 2008-10-03 Last updated: 2009-03-26Bibliographically approved

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