Do halogen and methyl substituents have electronic effects on the structures of simple disilanes? An experimental and theoretical study of the molecular structures of the series X3SiSiMe3 (X = H, F, Cl and Br)

The gas-phase molecular structures of a series of halogen-substituted disilanes [X₃SiSiMe₃ (X = H, F, Cl and Br)], 1,1,1-trimethyldisilane (H₃SiSiMe₃), 1,1,1-trifluoro-2,2,2-trimethyldisilane (F₃SiSiMe₃), 1,1,1-trichloro-2,2,2-trimethyldisilane (Cl₃SiSiMe₃) and 1,1,1-tribromo-2,2,2-trimethyldisilane (Br₃SiSiMe₃), have been determined in the gas phase by electron diffraction. Ab initio calculations at the HF and MP2 level were used to support the experimental investigation using the SARACEN method. All of the investigated structures were determined to adopt a staggered structure with C _3v symmetry. The effect of substitution on the Si–Si bond and the Si–Si–X bond angle was investigated and these results were compared to results obtained from a recent study of halogen-substituted disilanes [X₃SiSiXMe₂ (X = F, Cl, Br and I)] to consider the effect of the methyl groups on the substituted disilanes.     

Selective formation of non-conjugated olefins by samarium(II)-mediated elimination/isomerization of allylic benzoates

Aromatic allylic benzoates can be selectively transformed to the corresponding benzoate eliminated olefin by the action of samarium diiodide. Depending on the substrate and the elimination conditions, high selectivity for the non-conjugated alkene product can be achieved.     

Inclusion complex formation of β-cyclodextrin and Naproxen: a study on exothermic complex formation by differential scanning calorimetry

Inclusion complex formation between β-cyclodextrin and Naproxen was investigated using differential scanning calorimetry (DSC) as a function of the β-cyclodextrin-to-Naproxen molar ratio, ranging from 0:5:1 to 5:1. When these mixtures are heated above the melting temperature of Naproxen, an exothermic peak is observed at a temperature slightly higher than the melting peak of Naproxen. This peak, which has not been previously reported, has been interpreted as an exothermic energy of inclusion complex formation. The magnitude of this complex formation peak was found to be dependent upon the composition of the β-cyclodextrin and Naproxen mixture and increased in magnitude to a maximum value at a β-cyclodextrin:Naproxen molar ratio of 2:1. In addition, Naproxen recrystallization and re-melting peaks seen in the cooling and re-heating scans, respectively, decreased in magnitude with increasing molar ratio and totally disappeared for the mixture with 5:1 of β-cyclodextrin to Naproxen ratio indicative of complete inclusion of Naproxen in the cyclodextrin cavities. Complete inclusion was further reflected by the disappearance of key Naproxen peaks in Fourier transform infrared spectra of samples recovered from DSC experiments. The large excess of β-cyclodextrin needed to fully complex the Naproxen was found to be due to slow kinetics. Increasing the hold time after the initial melting led to inclusion efficiencies up to 95 % even for the 2:1 mixture. These experiments suggest that ratios of β-cyclodextrin:Naproxen 2:1 or greater facilitate the process by increasing the presence of cyclodextrin molecules in the close proximity of the drug molecules and lead to high inclusion efficiencies.