Refine
Has Fulltext
- no (13)
Document Type
- Article (13)
Language
- English (13)
Is part of the Bibliography
- yes (13)
Keywords
- Conformational analysis (2)
- Quantum chemical calculations (2)
- conformational analysis (2)
- quantum chemical calculations (2)
- 1,3-Azasilinanes (1)
- 1,3-Dimethyl-3-phenyl-1,3-azasilinane (1)
- 1,3-Oxasilinanes (1)
- 3-Silatetrahydropyrans (1)
- 3-silathianes (1)
- Assignment of stereochemistry (1)
- Barrier to ring inversion (1)
- Conformational equilibrium (1)
- DFT theoretical calculations (1)
- Dynamic NMR spectroscopy (1)
- Gas-phase electron diffraction (1)
- Low temperature NMR spectroscopy (1)
- NBO analysis (1)
- Ring current effect (1)
- Solvent effects (1)
- barrier to ring inversion (1)
- conformational equilibrium (1)
- dynamic NMR (1)
- low temperature NMR spectroscopy (1)
- low-temperature NMR spectroscopy (1)
- silapiperidines (1)
Institute
- Institut für Chemie (13)
3-Methyl-3-silatetrahydropyran 1 was synthesized and its molecular structure and conformational behavior was studied by gas-phase electron diffraction (GED), FTIR, low temperature H-1 and C-13 NMR spectroscopy, and by theoretical calculations (DFT, MP2). Two conformers; 1-ax and 1-eq; were located on the potential energy Surface. In the gas phase; a slight predominance of the axial conformer was determined, with the ratio 1-ax:1-eq = 54(9):46(9) (from GED) or 53:47 or 61;39 (from IR). In solution, LT NMR spectroscopy at 103 K gives the ratio 1-ax:1-eq = 35:65 (-Delta G(103)degrees = 0.13 kcal/mol). Simulation of solvent effects using the PCM continuum model or by calculation of the corresponding solvent-solute complexes allowed us to rationalize the experimentally observed opposite conformational predominance of the conformers of 3-methyl-3-silatettahydropyran in the gas phase and in solution. Comparative analysis of the effect of heteroatom in 1-hetero-3-methyl-3-silacyclohexanes on the structure, stereoelectronic interactions, and relative energies of the conformers is done.
1,3-Dimethyl-3-phenyl-1,3-azasilinane was synthesized and its conformational behavior was studied by the low temperature NMR spectroscopy and quantum chemical calculations. The compound was shown to exist as an equilibrium mixture of the PhaxMeeq and PheqMeax chair conformers with the N-methyl substituent in equatorial position. The barrier to ring inversion was also determined.
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 1H and 13C NMR spectroscopy and DFT theoretical calculations. In contrast to the expectations from the conformational energies of methyl and alkoxy substituents, the Meaxi-PrOeq conformer was found to predominate in the conformational equilibrium in the ratio Meaxi-PrOeq : Meeqi-PrOax of ca. 2 : 1 as from the 1H and 13C 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.