Methyl modified siloxane melting gels for hydrophobic films

Hybrid melting gels were prepared by a sol–gel process, starting with a mono-substituted siloxane and a di-substituted siloxane. Methyl-modified melting gels were prepared using (a) methyltriethoxysilane (MTES) with dimethyldiethoxysilane (DMDES) and (b) methyltrimethoxysilane (MTMS) together with dimethyldimethoxysilane (DMDMS). The gels with MTES–DMDES were prepared with concentrations between 50–50 and 75–25 mol%. The gels with MTMS–DMDMS were prepared with concentrations between 50–50 and 70–30 mol%. For both systems, the consolidation temperature, after which the melting gel no longer softens, increased with an increase in the amount of the mono-substituted siloxane, increasing from 135 to 160 °C for MTES–DMDES and increasing from 145 to 170 °C for MTMS–DMDMS. Coatings formed on mica substrates were about 1 mm thick, and showed no visible cracks. The surfaces of the coatings were profiled using micro-Raman spectroscopy, which revealed that methyl groups were concentrated at the surfaces of the films. All contact angles measured with water were greater than 90°.     

An investigation of structure-reactivity relationships of δ-alkenyl oximes; competitive thermal reactions leading to cyclic nitrones and/or N-unsubstituted bicyclic isoxazolidines

Thermal reactions of C-aryl δ-alkenyl oximes give N-unsubstituted bicylic lactone, lactam and pyrrolidine fused isoxazolidines by an intramolecular oxime olefin cycloaddition pathway (IOOC) and/or cyclic nitrones by an azaprotio cyclotransfer (APT) route; a number of factors, including the nature of the aryl group, the oxime geometry and the structure of the linker between the oxime and the terminal alkene, contribute to the competition.     

Direct Time‐Domain Observation of Conformational Relaxation in Gas‐Phase Cold Collisions

Cooling molecules in the gas phase is important for precision spectroscopy, cold molecule physics, and physical chemistry. Measurements of conformational relaxation cross sections shed important light on potential energy surfaces and energy flow within a molecule. However, gas‐phase conformational cooling has not been previously observed directly. In this work, we directly observe conformational dynamics of 1,2‐propanediol in cold (6 K) collisions with atomic helium using microwave spectroscopy and buffer‐gas cooling. Precise knowledge and control of the collisional environment in the buffer‐gas allows us to measure the absolute collision cross‐section for conformational relaxation. Several conformers of 1,2‐propanediol are investigated and found to have relaxation cross‐sections with He ranging from σ=4.7(3.0)×10^?18 cm² to σ>5×10^?16 cm². Our method is applicable to a broad class of molecules and could be used to provide information about the potential energy surfaces of previously uninvestigated molecules.     

Total Synthesis,Stereochemical Assignment,and Field‐Testing of the Sex Pheromone of the Strepsipteran Xenos peckii

The sex pheromone of the endoparasitoid insect Xenos peckii (Strepsiptera: Xenidae) was recently identified as (7E,11E)‐3,5,9,11‐tetramethyl‐7,11‐tridecadienal. Herein we report the asymmetric synthesis of three candidate stereostructures for this pheromone using a synthetic strategy that relies on an sp³–sp² Suzuki–Miyaura coupling to construct the correctly configured C7‐alkene function. Comparison of ¹H NMR spectra derived from the candidate stereostructures to that of the natural sex pheromone indicated a relative configuration of (3R*,5S*,9R*). Chiral gas chromatographic (GC) analyses of these compounds supported an assignment of (3R,5S,9R) for the natural product. Furthermore, in a 16‐replicate field experiment, traps baited with the synthetic (3R,5S,9R)‐enantiomer alone or in combination with the (3S,5R,9S)‐enantiomer captured 23 and 18 X. peckii males, respectively (mean±SE: 1.4±0.33 and 1.1±0.39), whereas traps baited with the synthetic (3S,5R,9S)‐enantiomer or a solvent control yielded no captures of males. These strong field trapping data, in combination with spectroscopic and chiral GC data, unambiguously demonstrate that (3R,5S,9R,7E,11E)‐3,5,9,11‐tetramethyl‐7,11‐tridecadienal is the X. peckii sex pheromone.     

Catalytic enantioselective Conia-ene reaction

An enantioselective intramolecular Conia-ene reaction of beta-dicarbonyl compounds and alkynes to afford methylene cyclopentanes is described. The reaction employs a DTBMSegphos-Pd(II)/Yb(III) dual catalyst system that allows for the asymmetric synthesis of all-carbon quaternary centers and generates a product containing an alkene that can be further manipulated.     

Macrocyclic Cyclopropenes by Highly Enantioselective Intramolecular Addition of Metal Carbenes to Alkynes

The intramolecular addition of a diazo ester group to a triple bond in the presence of chiral dirhodium(II ) carboxamidate catalysts gives macrocyclic lactones with a fused cycloproprene ring [Eq. (a)]. This efficient reaction is characterized by high enantiocontrol (up to 98% ee) and chemoselectivity.     

4′‐Hydro­xy­bi­phenyl‐4‐carbo­nitrile

The title compound, C₁₃H₉NO, crystallizes with four mol­ecules in the asymmetric unit. Each of the four crystallographically independent mol­ecules forms a chain parallel to the a axis with symmetry‐equivalent mol­ecules. These chains are held together by similar O—H·NC hydrogen bonds, with approximately linear O—H·N angles and significantly bent H·N—C angles. The four different mol­ecules are related by strong elements of pseudosymmetry. To better describe the pseudosymmetry, the structure has been reported in the non‐standard space group .     

Powder‐XRD and 14N magic angle‐spinning solid‐state NMR spectroscopy of some metal nitrides

Some metal nitrides (TiN, ZrN, InN, GaN, Ca₃N₂, Mg₃N₂, and Ge₃N₄) have been studied by powder X‐ray diffraction (XRD) and ¹⁴N magic angle‐spinning (MAS) solid‐state NMR spectroscopy. For Ca₃N₂, Mg₃N₂, and Ge₃N₄, no ¹⁴N NMR signal was observed. Low speed (ν_r = 2 kHz for TiN, ZrN, and GaN; ν_r = 1 kHz for InN) and ‘high speed’ (ν_r = 15 kHz for TiN; ν_r = 5 kHz for ZrN; ν_r = 10 kHz for InN and GaN) MAS NMR experiments were performed. For TiN, ZrN, InN, and GaN, powder‐XRD was used to identify the phases present in each sample. The number of peaks observed for each sample in their ¹⁴N MAS solid‐state NMR spectrum matches perfectly well with the number of nitrogen‐containing phases identified by powder‐XRD. The ¹⁴N MAS solid‐state NMR spectra are symmetric and dominated by the quadrupolar interaction. The envelopes of the spinning sidebands manifold are Lorentzian, and it is concluded that there is a distribution of the quadrupolar coupling constants Q_cc's arising from structural defects in the compounds studied. Copyright © 2015 John Wiley & Sons, Ltd.