Gas phase structures, energetics, and potential energy surfaces of disilacyclohexanes.

The molecular structures of 1,4-, 1,3-, and 1,2-disilacyclohexanes (denoted as 14, 13, and 12, respectively) were investigated by means of gas electron diffraction (GED). Each molecule was found to possess a chair as the most stable conformation in the gas phase, the point group being C(2h), C(s), and C(2), respectively. Experimental GED structures are in good agreement with theoretical calculations (MP2/cc-pVTZ and B3LYP/cc-pVTZ).

Experimental design for optimizing drug release from silicone elastomer matrix and investigation of transdermal drug delivery.

Silicone elastomers are commonly used for medical devices and external prosthesis. Recently, there has been growing interest in silicone-based medical devices with enhanced function that release drugs from the elastomer matrix. In the current study, an experimental design approach was used to optimize the release properties of the model drug diclofenac from medical silicone elastomer matrix, including a combination of four permeation enhancers as additives and allowing for constraints in the properties of the material.

First synthesis of the three isomeric parent disilacyclohexanes. An improved preparation of methylene di-Grignard.

Ring closure of 1,5-dibromo-1,5-disilapentane with methylene di-Grignard was the key step in the preparation of the parent 1,3-disilacyclohexane. For that purpose, the preparation of methylene di-Grignard has been improved and simplified. The successful synthesis of the isomeric 1,2- and 1,4-disilacyclohexanes is also reported.

Unexpected conformational properties of 1-trifluoromethyl-1-silacyclohexane, C5H10SiHCF3: gas electron diffraction, low-temperature NMR spectropic studies, and quantum chemical calculations.

The molecular structure of axial and equatorial conformers of 1-trifluoromethyl-1-silacyclohexane, (C5H10SiHCF3), as well as the thermodynamic equilibrium between these species was investigated by means of gas electron diffraction (GED), dynamic nuclear magnetic resonance (DNMR) spectroscopy, and quantum chemical calculations (B3LYP, MP2, and CBS-QB3). According to GED, the compound exists as a mixture of two Cs symmetry conformers possessing the chair conformation of the six-membered ring and differing in the axial or equatorial position of the CF3 group (axial=58(12) mol%/equatorial=42(12) mol%) at T=293 K. This result is in a good agreement with the theoretical prediction.

Conformations of silicon-containing rings. 5. Conformational properties of 1-methyl-1-silacyclohexane: gas electron diffraction, low-temperature NMR, and quantum chemical calculations.

The molecular structure of 1-methyl-1-silacyclohexane 3 has been determined by gas electron diffraction (GED). The conformational preference of the methyl group was studied experimentally in the gas phase (GED) and in solution (low-temperature (13)C NMR) and by quantum chemical calculations (HF, MP2, and B3LYP with 6-31G basis sets and mPW1PW91/6-311G(2df,p)). Both experimental methods result in a preference of the equatorial position of the methyl group, 68(7)% in the gas phase at 298 K and 74(1)% in solution at 110 K.