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Conformation and Stereodynamics of Aliphatic Triisopropylsilanes in Solution and in the Solid State
Author(s) -
Anderson J. Edgar,
Casarini Daniele,
Lunazzi Lodovico,
Mazzanti Andrea
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(200002)2000:3<479::aid-ejoc479>3.0.co;2-#
Subject(s) - chemistry , solid state , computational chemistry , stereochemistry , crystallography , chemical physics
A dynamic process has been detected in the solution 13 C‐NMR spectra of t Bu‐Si( i Pr) 3 ( 4 ) in the temperature range ‐145 °C to ‐163 °C, the corresponding free energy of activation being 5.5 kcal mol −1 . Molecular mechanics calculations have identified three types of conformations that are markedly more stable than all the others, but the one with the highest symmetry cannot be populated, as is evident from the appearance of the spectrum at low temperature. This spectrum can be interpreted in terms of restricted rotation of the tert ‐butyl group and of the isopropyl groups, leading to a structure centered around the ( a , g ,‐ g ) conformation. In the case of the analogous ( i Pr) 3 SiCl derivative ( 5 ), this dynamic process was not observed in solution, but an appropriate spectrum for the same ( a , g ,‐ g ) conformation was obtained by the solid‐state CP‐MAS NMR spectroscopy at ‐100 °C.