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Unusual conformational preferences of 1,3‐dimethyl‐3‐isopropoxy‐3‐silapiperidine
Author(s) -
Kirpichenko Svetlana V.,
Shainyan Bagrat A.,
Kleinpeter Erich
Publication year - 2012
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3028
Subject(s) - chemistry , conformational isomerism , ring flip , alkoxy group , nuclear magnetic resonance spectroscopy , ring (chemistry) , activation barrier , entropy (arrow of time) , computational chemistry , crystallography , stereochemistry , molecule , density functional theory , thermodynamics , organic chemistry , alkyl , physics
The conformational analysis of the first representative of the Si‐alkoxy substituted six‐membered Si,N‐heterocycles, 1,3‐dimethyl‐3‐isopropoxy‐3‐silapiperidine, was performed by low‐temperature 1 H and 13 C NMR spectroscopy and DFT theoretical calculations. In contrast to the expectations from the conformational energies of methyl and alkoxy substituents, the Me ax i ‐PrO eq conformer was found to predominate in the conformational equilibrium in the ratio Me ax i ‐PrO eq : Me eq i ‐PrO ax of ca. 2 : 1 as from the 1 H and 13 C NMR study. The thermodynamic parameters obtained by the complete line shape analysis showed that the main contribution to the barrier to ring inversion originates from the entropy term of the free energy of activation. Copyright © 2012 John Wiley & Sons, Ltd.