The stannylation of carbonyl-stabilised phosphorus ylids,and tin-assisted elimination reactions

The interaction of organotin halides with lithium salts of mono-substituted phosphorus ylids and also with disubstituted ylids is described.     

Nickelocene chemistry : III. Reactions of Bromo(η5-cyclopentadienyl)triphenylphosphinenickel with phosphorus,arsenic and sulphur ylids

The phosphorus ylids Ph₃PCHR (R = Me, Et, Prⁿ, Prⁱ, Bu_n, Cl, and OMe), and the ylids Ph₃AsCH₂, Me₂SCH₂, and Me₂S(O)CH₂ react with [Ni(η⁵-C₅H₅)Br(PPh₃)] at room temperature to give the complexes [Ni(Ph₃PCHR)(η⁵-C₅H₅(PPh₃)] Br, [Ni(Ph₃AsCH₂)(η⁵-C₅H₅)(PPh₃)]Br, [Ni(Me₂SCH₂)(η⁵-C₅H₅)(PPh₃)]Br and [Ni{Me₂S(O)CH₂} (η⁵-C₅H₅)(PPh₃)]Br, respectively. These are readily converted into the corresponding hexafluorophosphate salts on reaction with ammonium hexafluorophosphate. Under more forcing conditions the stabilised ylid Ph₃PCHCOPh gives a product believed to be the complex [Ni(Ph₃PCHCOPh)₂(η⁵-C₅H₅)]Br, isolated and characterised as its PF₆^? salt.     

Dose distribution in electron-irradiated PMMA: effect of dose and geometry

Depth-dose distributions for an electron beam are generally determined with either a stack irradiation geometry or a wedge (generally with an angle of about 50°–60°) made from an electrically-conducting material (such as, aluminium) or a non-conducting material (such as, PMMA). If the non-conducting wedge is thicker than the electron range, the stored charge in the material could influence the measured depth-dose distribution. This effect was investigated for 7-MeV electrons for PMMA with the wedge angle varying from 0° to 60°. The maximum-to-surface dose ratio was used as a characteristic parameter of the shape of the distribution. The depth-dose distribution measured by a dosimetry film placed inside the wedge-pair was similar to the standard shape when the wedge angle was larger than about 55° (dose ratio 1.5). However, as the angle was decreased, this ratio sharply increased almost linearly up to about 15°, and then leveled off at about 3. We also studied the effect of the surface dose on this dose ratio for the wedge angle of 0°, where we found that the ratio increased with the dose. Both of these effects can be explained by the presence of the electrostatic field around the dosimetry film due to stored charge in the non-conducting PMMA.     

About the structure of cellulose: debating the Lindman hypothesis

The hypothesis advanced in this issue of CELLULOSE [Springer] by Bjorn Lindman, which asserts that the solubility or insolubility characteristics of cellulose are significantly based upon amphiphilic and hydrophobic molecular interactions, is debated by cellulose scientists with a wide range of experiences representing a variety of scientific disciplines. The hypothesis is based on the consideration of some fundamental polymer physicochemical principles and some widely recognized inconsistencies in behavior. The assertion that little-recognized (or under-estimated) hydrophobic interactions have been the reason for a tardy development of cellulose solvents provides the platform for a debate in the hope that new scientific endeavors are stimulated on this important topic.     

Studies on cycloimmonium ylids. Synthesis of some new 2,4,6-triaryl-substituted pyridines via pyridinium,picolinium and isoquinolinium ylids

Reaction of pyridinium phenacylids and their picolinium and isoquinolinium counterparts with substituted benzylideneacetophenones gave a wide variety of 2,4,6-triaryl-substituted pyridines which are expected to have some potential biological activities. Ammonium acetate in glacial acetic acid was used as the cyclization agent. The structures of resulting pyridines are supported by nmr and ir spectral data.     

On the shell structure and geometry of monovalent metal clusters

The Hückel model is used to study the electronic structure of monovalent metal clusters. In an fcc cluster the Hückel model gives an estimate to the electronic structure of a free electron cluster. It is shown that the surface faceting of the fcc cluster can destroy the electronic shell structure already when the cluster has about 100 electrons. In the Hückel model the icosahedral structure has smaller total energy than the fcc structures, from which the Wulff construction has the smallest energy already when the cluster has 600 atoms.     

End-substitution effect on the geometry and electronic structure of oligoheterocyclics

The end-substitution effects on the geometric and electronic structures of oligoheterocyclics are systematically studied using the density functional theory. It is found that the influence of the end-substitution does not depend on the heteroatom. End-substitution plays a fine-tune effect on the geometry and the excitation state. While the influences on the conducting type (p-type or n-type) and the inter-chain charge carrier hoping channels are much different between the electron-donating –CH ₃ and electron–accepting –CN substitutions. Both molecular electrostatic potentials and charge carrier injection rates indicate that the –CH ₃/–CH ₃ substitution is beneficial to the p-type doping, while the –CN/–CN substitution is in favor of the n-type doping, which is in agreement with the experimental observations. The –CH ₃ substituted packing dimers exert similar intermolecular interactions to the unsubstituted ones. The –CN substituted packing dimers yield much stronger intermolecular interactions comparing to the –CH ₃ substituted ones. It could be anticipated that the –CN substitution would be helpful to the charge carrier hopings between chains and thereby enhance the conductivity.     

Substitution effect on the geometry and electronic structure of the ferrocene

The substitution effects on the geometry and the electronic structure of the ferrocene are systematically and comparatively studied using the density functional theory. It is found that -NH(2) and -OH substituents exert different influence on the geometry from -CH(3), -SiH(3), -PH(2), and -SH substituents. The topological analysis shows that all the C-C bonds in a-g are typical opened-shell interactions while the Fe-C bonds are typical closed-shell interactions. NBO analysis indicates that the cooperated interaction of d --> pi* and feedback pi --> d + 4s enhances the Fe-ligand interaction. The energy partitioning analysis demonstrates that the substituents with the second row elements lead to stronger iron-ligand interactions than those with the third row elements. The molecular electrostatic potential predicts that the electrophiles are expected to attack preferably the N, O, P, or S atoms in Fer-NH(2), Fer-OH, Fer-PH(2), and Fer-SH, and attack the ring C atoms in Fer-SiH(3) and Fer-CH(3). In turn, the nucleophiles are supposed to interact predominantly by attacking the hydrogen atoms. The simulated theoretical excitation spectra show that the maximum absorption peaks are red-shifted when the substituents going from second row elements to the third row elements.     

Ab-initio studies of fluoroxytrifluoromethane geometry and electronic structure

Ab-initio molecular orbital calculations using both minimal or STO-3G and extended or 4-31G basis sets have been applied to fluoroxytrifluormethane. Complete geometry optimizations using both basis sets have been applied to this molecule and the calculated structural parameters have been compared to the electron diffraction data. The extended basis set calculations are found to be in much better overall agreement with experiment although the minimal basis set does reproduce the angular parameters well, including the tilt angle. The barrier to the CF₃ torsion has been computed and it compares favorably with the microwave spectral value.The electronic structure of CF₃OF and some related molecules have been examined by partitioning the electrons according to the method of Mulliken. The highest occupied orbital in CF₃OF is found to be largely an O-F π * orbital and the O-F bond is also found to be the least ionic and weakest bond in the molecule. The computed dipole moment of CF₃OF agrees well with the experimental value.     

Characterization of ylids formed during the photolysis of α-epoxyketones

The irrdiation of α-epoxyketones $\text{1}$ – $\text{3}$ at 366 nm produced ylids which were characterized by their absorption spectra and by trapping with maleic anhydride.     

Total phosphorus distribution over the Baltic Sea sub-regions

A quantitative relation has been revealed between the input and concentration of total phosphorus in different sub-regions of the Baltic Sea. This relation has been used to calculate the total phosphorus content of water in the Baltic Sea in 1990, 1995, 2000, and 2006.     

New evidence for and new reactions of ortho-lithio ylids

While α-lithio ylid 2 my be generated from triphenylphosphonio-bromomethylid through halogen/metal exchange, the reaction of triphenyl phosphonio-methylid 1 with sec- or tert-butyllithium produces nearly quantitatively the o-lithio ylid 3 , which is stable at -60° but slowly decomposes at higher temperatures via a cyclization product 5 to give the α-lithio phosphine 4.     

Synthesis and properties of thiocarbamoylmethylpyridinium (isoquinolinium) ylids

2-(2-Carbethoxy-1-amino-1-thio)ethylenepyradinium(isoqunolinium) ylids were obtained by the reaction of carbethoxycyanomethylpyridinium(isoquinolinium) ylids with hydrogen sulfide. In an alkaline medium they cyclize into 5-mercaptosubstituted imidazo[1,2-a]pyridines(isoquinolines). The structure of the latter compounds was confirmed by PMR and IR spectroscopy.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1639–1643, December, 1989.     

Nitrones—V: Reactions of some nitrones with phosphinoxy ylids

Reactions of 3,4-dihydroisoquinoline N-oxide (1) with carbomethoxymethyldiphenylphosphine oxide (13) and cyanomethyldiphenylphosphine oxide (14) lead both in 1,2-dimethoxyethane (DME) and in t-BuOH mostly to enamines 6 and 7 respectively. In contrast reactions of 5,5-dimethyl-Δ¹-pyrroline N-oxide (2) with 13 and 14 lead to mixtures of aziridines 8 or 9 and of enamines 10 or 11, respectively, in the aprotic solvent DME. These reactions give only aziridines 8 or 9 in t-BuOH. The results obtained are explained in terms of the formation of pentacoordinated phosphorus intermediates.