Silabutadienes. Internal rotations and pi-conjugation. A density functional theory study
Hong-Wei Xi1, Miriam Karni, Yitzhak Apeloig
1Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel.
The Journal of Physical Chemistry. A
|October 15, 2008
Summary
Computational studies reveal that silabutadienes exhibit varying stable conformations, with rotation barriers influenced by central bond length and pi-conjugation. These barriers, while correlating with conjugation, do not solely determine resonance energies.
Area of Science:
- Computational Chemistry
- Organic Chemistry
- Materials Science
Background:
- Silabutadienes are silicon-containing analogs of butadiene with potential applications in materials science.
- Understanding their conformational preferences and rotational dynamics is crucial for predicting their properties.
Purpose of the Study:
- To computationally investigate the potential energy surfaces (PESs) for internal rotation in nine different silabutadienes.
- To determine the most stable conformers and analyze the factors influencing internal rotation barriers (RB).
- To explore the relationship between RB and pi-conjugation energies.
Main Methods:
- Density Functional Theory (DFT) with the B3LYP functional and 6-311+G(d,p) basis set was employed for PES calculations.
- Conformational analysis identified stable rotamers (s-trans, antiperiplanar, gauche).
- Resonance stabilization energies (RE) were estimated using Natural Bond Orbital (NBO) and Block Localized Wave function (BLW) methods.
Main Results:
- The s-trans rotamer is most stable for silabutadienes with C-C central bonds, while antiperiplanar conformers are favored for those with trans-bent SiSi double bonds.
- Internal rotation barriers (RB) vary significantly, with the shortest central bonds exhibiting the highest barriers.
- A linear correlation was observed between RB and pi-conjugation energies, though RBs are smaller than REs.
Conclusions:
- Central bond length is a primary determinant of rotation barriers in silabutadienes.
- While pi-conjugation influences RB, it is not the sole factor, and RBs cannot be used to estimate absolute resonance energies.
- The study provides insights into the structure-property relationships of silabutadienes, relevant for designing new silicon-based materials.
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