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Why is the Si-X stretching frequency of X8Si8O12 (X = H, CH3, Cl) much higher than that of XSi(OSiME3)3?

Why is the Si-X stretching frequency of X8Si8O12 (X = H, CH3, Cl) much higher than that of... The totally symmetric stretching frequencies u5(Si-X) of the octasilases-quioxanes X8Si8O12 are distinctively larger than those of XSi(OSiMe3)3 for X = H, CH3, Cl whereas u5(Si-H) of H8Si8O12 and of H10Si10O15 differ very little. Inspection of the experimental data and molecular orbital calculations of the EHMO-ASED type show that this striking discrepancy is caused by the differences in the X-Si-O-Si conformations. The cage structure of X2Si8O12 requires the anti X-Si-O-Si conformation whereas the syn conformation is the stable one in XSi(OSiMe3)3. The Si-H bond order decreases from anti to syn caused by a decreasing interaction of the H-ls orbital with the Si-O-pπ type orbitals. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Research on Chemical Intermediates Springer Journals

Why is the Si-X stretching frequency of X8Si8O12 (X = H, CH3, Cl) much higher than that of XSi(OSiME3)3?

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References (17)

Publisher
Springer Journals
Copyright
Copyright
Subject
Chemistry; Catalysis; Physical Chemistry; Inorganic Chemistry
ISSN
0922-6168
eISSN
1568-5675
DOI
10.1163/156856795X00431
Publisher site
See Article on Publisher Site

Abstract

The totally symmetric stretching frequencies u5(Si-X) of the octasilases-quioxanes X8Si8O12 are distinctively larger than those of XSi(OSiMe3)3 for X = H, CH3, Cl whereas u5(Si-H) of H8Si8O12 and of H10Si10O15 differ very little. Inspection of the experimental data and molecular orbital calculations of the EHMO-ASED type show that this striking discrepancy is caused by the differences in the X-Si-O-Si conformations. The cage structure of X2Si8O12 requires the anti X-Si-O-Si conformation whereas the syn conformation is the stable one in XSi(OSiMe3)3. The Si-H bond order decreases from anti to syn caused by a decreasing interaction of the H-ls orbital with the Si-O-pπ type orbitals.

Journal

Research on Chemical IntermediatesSpringer Journals

Published: Mar 16, 2009

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