The true potential energy curves for different states of SiO and SiS molecules

The true potential energy curves forX ¹ Σ ⁺, a³ π _r,A ¹ π,e ³ Σ ⁻,E ¹ Σ ⁺,c ³ π _i states of astrophysically important molecule SiO, whose spectra were observed in the sunspots, have been constructed using the method of Lakshman and Rao. Dissociation energy and ionization potential have been estimated as 65,350 cm⁻¹ and 92,854 cm⁻¹ respectively and found to be in good agreement with the values cited in literature. The true potential energy curves forX ¹ Σ ⁺,D ¹ π andE ¹ Σ ⁺ states of SiS molecule have been constructed by the same method and its dissociation energy in the ground state has been estimated using Hulburt-Hirschfelder potential function as 54,765 cm⁻¹ in good agreement with 53,250.9 cm⁻¹ given by Herzberg.     

2-(o-Hydroxyanilido)alkylnitriles vs. 2-[1-(o-hydroxyanilido)alkyl]-benzoxazoles as products from o-aminophenol and cyanohydrins

The reaction of o-aminophenol with cyanohydrins leads to the formation of novel benzoxazoles 2 or the expected 2-(o-hydroxyanilido)alkylnitriles 3 or mixtures of these two, depending on the alkyl substituents on the cyanohydrin. The formation of benzoxazoles 2 was found to be due to the intrinsic instability of the corresponding 2-(o-hydroxyanilido)alkylnitriles, such as 4 .     

Ring opening metathesis polymerisations of norbornene and norbornadiene derivatives containing oxygen: a study on the regeneration of Grubbs catalyst

Ring opening metathesis polymerisation (ROMP) of norbornene and norbornadiene derivatives containing oxygen are investigated using Grubbs well-defined ruthenium initiator. A series of 7-alkoxy norbornadiene monomers (2b-d), containing alkoxy groups with decreasing steric hindrance in the 7-position have been prepared. The ROMP reactions of monomers showed that as the reaction proceeds the initiator is consumed first and then is partially regenerated at the expense of the propagating species. A small amount of another carbene species X, giving a broad signal at 17.44 ppm, is also formed which is extremely stable in solution. The species X is an active metathesis species and is able to perform ROMP on strained cyclic olefins. ROMP of monomers without alkoxy groups in the 7-position (3, 4a, 4b, 5a and 5b) and also monomers with alkoxy groups in the 5 and/or 6 positions of norbornene (6 and 7) have been performed under similar conditions. None of these systems exhibited regeneration of the initiator and no resonances due to species X can be seen in the ¹H NMR spectra. The results confirm that the presence of oxygen in the 7-position of the norbornadiene monomer plays an important role in the process of regeneration of the initiator. It is found that the steric bulk and the position of substituents of the monomer have a pronounced influence on the extent of regeneration of the initiator.     

Cationic crosslinking of solid dgeba resins with ytterbium(III) trifluoromethanesulfonate as initiator

Solid bisphenol-A epoxy resin of medium molecular mass was cured using a Lewis acid initiator (ytterbium(III) trifluoromethanesulfonate) in three different proportions (0.5, 1 and 2 phr). A kinetic study was performed in a differential scanning calorimeter. The complete kinetic triplet was determined (activation energy, pre-exponential factor, and integral function of the degree of conversion) for each system. A kinetic analysis was performed with an integral isoconversional procedure (free model), and the kinetic model was determined both with the Coats-Redfern method (the obtained isoconversional value being accepted as the effective activation energy) and through the compensation effect. All the systems followed the same isothermal curing model simulated from non-isothermal ones. The growth-of-nuclei Avrami kinetic model A_3/2 has been proposed as the polymerization kinetic model. The addition of initiator accelerated the reaction especially when 2 phr was added. 0.5 and 1 phr showed very few kinetic differences between them.     

Rapid synthesis and zebrafish evaluation of a phenanthridine-based small molecule library

A Heck cyclisation approach is described for the rapid synthesis of a library of natural product-like small molecules, based on the phenanthridine core. The synthesis of a range of substituted benzylamine building blocks and their incorporation into the library is reported, together with a highly selective cis-dihydroxylation protocol that enables access to the target compounds in an efficient manner. Biological evaluation of the library using zebrafish phenotyping has led to the discovery of compound 20c, a novel inhibitor of early-stage zebrafish embryo development.     

An analytical investigation of 24 oxygenated-PAHs (OPAHs) using liquid and gas chromatography–mass spectrometry

We developed two independent approaches for separation and quantitation of 24 oxygenated polycyclic aromatic hydrocarbons (OPAHs) using both liquid chromatography-atmospheric pressure chemical ionization/mass spectrometry (LC-APCI/MS) and gas chromatography-electron impact/mass spectrometry (GC-EI/MS). Building on previous OPAH research, we examined laboratory stability of OPAHs, improved existing method parameters, and compared quantification strategies using standard addition and an internal standard on an environmental sample. Of 24 OPAHs targeted in this research, 19 compounds are shared between methods, with 3 uniquely quantitated by GC-EI/MS and 2 by LC-APCI/MS. Using calibration standards, all GC-EI/MS OPAHs were within 15 % of the true value and had less than 15 % relative standard deviations (RSDs) for interday variability. Similarly, all LC-APCI/MS OPAHs were within 20 % of the true value and had less than 15 % RSDs for interday variability. Instrument limits of detection ranged from 0.18 to 36 ng mL^?1 on the GC-EI/MS and 2.6 to 26 ng mL^?1 on the LC-APCI/MS. Four standard reference materials were analyzed with each method, and we report some compounds not previously published in these materials, such as perinaphthenone and xanthone. Finally, an environmental passive sampling extract from Portland Harbor Superfund, OR was analyzed by each method using both internal standard and standard addition to compensate for potential matrix effects. Internal standard quantitation resulted in increased precision with similar accuracy to standard addition for most OPAHs using 2-fluoro-fluorenone-¹³C as an internal standard. Overall, this work improves upon OPAH analytical methods and provides some considerations and strategies for OPAHs as focus continues to expand on this emerging chemical class.

Template synthesis of 1,4,7-triphosphacyclononanes

Iron(II) templates based on a [(eta(5)-Cp(R))Fe]+ core have been employed for the successful synthesis of 1,4,7-triphosphacyclononane derivatives (9-aneP3R'3) from a range of appropriately functionalized coordinated diphosphines and monophosphines. 1,2-Diphosphinoethane (1,2-dpe) or (2-phosphinoethyl)phenylphosphine (Phdpe) undergo a base-catalyzed Michael-type addition to trivinylphosphine, divinyl(benzyl)phosphine, or divinyl(phenyl)phosphine in [(eta(5)-Cp(R))Fe(diphosphine)(monophosphine)]+ complexes (2a-j) to give [(eta(5)-Cp(R))Fe(9aneP3R'3)]+ derivatives (4a-j) containing coordinated triphosphacyclononanes bearing one (with Phdpe) or two (with 1,2-dpe) secondary phosphine donors. The rates of macrocyclization show a dependence on the nature of the substituent(s) R on the cyclopentadienyl ligand with increased rates being observed along the series R = H5 < (Me3Si)H4 < 1,3-(Me3Si)2H3 approximately = Me5. For coupling reactions with trivinylphosphine, a pendant vinyl function remains in the macrocyclic product (4a-g) which is readily hydrogenated to the corresponding ethyl derivatives (5a-g). Further functionalization of coordinated secondary phosphines in the initially formed macrocycles (5a-g) is achieved by proton abstraction followed by addition of the appropriate alkyl halide electrophile and gives rise to tritertiary-triphospha-cyclononanes (7a-g, 7l, 7m). All new complexes have been fully characterized by spectroscopic and analytical methods in addition to the structural determination by single-crystal X-ray techniques of [{eta(5)-(Me3Si)2C5H3)Fe(9-aneP3H2C2H3)]PF6, 4c, and [(eta(5)-Me3SiC5H4)Fe(9-aneP3Et3)]BF4, 7b. 1,4,7-Triethyl-1,4,7-triphosphacyclononane is released from its metal template (7a, 7b) by treatment with either H2O2 or Br2/H2O to give the trioxide 9-aneP3(O)3Et3 (8). Attempts to recover the trivalent phosphorus species, 1,4,7-triethyl-1,4,7-triphosphacyclononane, from the trioxide by reduction proved unsuccessful.