Synthesis and crystal structures of some cobalt halide derivatives containing alkyl or silanolato groups

The alkylcobalt halide (2) and the lithium silanolatocobaltates Li(THF)₂(μ-Br)₂Co(μ-OSiMe₃)₂Co(μ-Br)₂Li(THF)₂ (4) and [LiBr{Li(THF)}₂{CoBr(OSiMe₃)₃}]₂ (5) form centrosymmetrical halogen-bridged dimers in the crystalline state. Compound 4 shows bromide bridges between lithium and cobalt, and silanolato bridges between the cobalt atoms. Below 200 K there are significant antiferromagnetic interactions between the cobalt centres. Compound 5 crystallises in a novel structure in which two cubane-like fragments containing silanolato bridges are linked together through a Li₂Br₂ ring.     

Dipole moments of some alkyl vinyl and alkyl propenyl ethers

Dipole moments of several alkyl vinyl and alkyl propenyl ethers have been determined by the Halverstadt-Kumler method in benzene solution at 293 K. The μ values depend on the bulkiness of the alkyl group present. In the alkyl vinyl ether series, a part of the varying μ values may be ascribed to changes in molecular geometry with varying bulkiness of the alkyl group. Other factors are clearly involved, since even in the alkyl (Z)-propenyl ether series μ values depend significantly on the alkyl group, although the geometry of the molecules remains essentially constant throughout the series. In the latter series, the total dipole moment is linearly related to the Taft's σ^*-values of the alkyl groups:μ/D=?(1.17±0.15)σ^*+(1.29±0.03). This suggests that the variation of μ with the alkyl radical follows from the changing polar character of the alkyl groups, which leads to changes in the value of the group moment μro.     

Unusual head-to-tail coupling of alkyl benzoates by electroreduction.

The electroreduction of alkyl benzoates in an alcoholic solvent gave unusual head-to-tail coupled products. Usual head-to-head coupled products derived from acyloin condensation could not be detected. The best result (73% yield) was obtained from methyl benzoate using an undivided cell with an Sn cathode in i-PrOH containing tetraalkylammonium salt as a supporting electrolyte. Using an undivided cell, the products cross-coupled with a solvent molecule were obtained as byproducts. The substitution at the para position of methyl benzoate considerably decreased the yields of the head-to-tail coupled products and increased those of the cross-coupled products. The possible mechanism of the head-to-tail coupling is the attack of anion radical, generated from methyl benzoate by one-electron transfer, to another methyl benzoate. The cross-coupled products were formed by the reaction with carbonyl compound anodically produced from a solvent molecule. The cross-coupling between methyl benzoate and aromatic aldehydes was also effected by the mixed electroreduction under the same conditions.     

Unusual nickel-mediated C-S cleavage of alkyl and aryl sulfoxides

The first examples of transition metal mediated C-S cleavage of sulfoxides containing sp2- and sp3-hybridized carbon bonds attached to the sulfur atom and the first example of a structurally characterized complex featuring an oxygen-bound sulfinyl ligand are presented.     

Mass spectra of some alkyl isoxazoles

The mass spectra of several compounds obtained during the process of Stork's isoxazole synthesis9 as well as the related isoxazoles have been investigated. The fragmentations of simple alkyl isoxazoles are nicely formulated via azirine intermediates. A striking difference between the spectra of isoxazoles and those of methylfurans as to the relative abundance of [M — l] peaks is noteworthy. The very low abundance of these peaks in the former reflects the unique character of isoxazole nucleus due to the preferential cleavage of N? O linkage rather than a benzylic C? H bond rupture. If an alkyl substituent is present at 4-position in 3,5-dimethylisoxazoles, strong peaks at m/e 110, 68 and 43 are common in their spectra. The analyses of metastable transitions and high resolution measurements have demonstrated that the formation of these ions can be interpreted by a mechanism involving the cleavage of N? O linkage.     

Unusual crystalline and polycrystalline structures in methane hydrates

We present previously unreported crystalline and polycrystalline structures for methane hydrates obtained at relatively low pressures. These structures, which contain unusual cages with 12 pentagonal faces and 3 hexagonal faces, were observed during the atomistic simulations of the crystal growth of sI and sII methane hydrates. These 51263 cages have a significant impact on the structure of the resulting crystal and could explain several experimental observations regarding in-situ transformations between sI and sII hydrates. We document a previously unidentified structure of methane hydrates which we designate structure sK. Additionally, we predict a polycrystalline structure consisting of this new hydrate and sI and suggest a mechanism for the formation of a polycrystalline structure consisting of sequences of sI and sII hydrates.     

Unusual adsorption behavior of polymers in layered structures

We studied the conformations of polymer chains embedded in regular lamellar matrices such as microphase-separated block copolymer melts or lipid/water systems. In such quasi-one-dimensional systems, the host plays the role of a nearly-periodic external potential. A probe chain can get trapped with the localization length L at isolated defects, when its degree of polymerization N exceeds a cross-over value N_L. Interestingly, the radius of gyration, R_g, of the chain displays a minimum as a function of the defect density, ρ, the minimum being estimated by ρ_cL ≃ N_L/N. Using Monte Carlo simulation, we underline the non-monotonic behavior of R_g and calculate Green's function for various defect densities. On the same vein, the mean square displacement of the monomer units at large times shows a pronounced minimum as a function of the defect density, ρ.     

Intramolecular rotation in some alkyl trifluoroacetates at mircowave frequencies

The permittivity and dielectric loss of methyl and ethyl trifluoroacetates have been measured at three microwave frequencies viz., 24.50, 18.26 and 9.83 GHz and also at 1 MHz and optical frequency at 35°C, in dilute solutions of benzene and decalin. The permittivity and dielectric loss at different frequencies have been plotted against concentration (wt. fraction). The slopes of these straight lines have been used for the complex plane plots (a″ vs a′), which in the case of benzene are Debye semi-circles for the main dispersion region while in decalin are Cole-Cole arcs which show symmetrical distribution of relaxation times. The dispersion curve for these compounds in decalin could not be resolved into two distinct Debye curves because of overlapping of the two dispersion regions. The data have been analysed in terms of two relaxation processes corresponding to overall and group rotations.     

Synthesis and structures of alkyl (aryl) benzazolylazoketoximes

Alkyl(aryl)benzazolylazoketoximes were obtained by nitrosation of the hydrazones of alkyl- and aryl-substituted aldehydes by means of n-amyl nitrite. On the basis of data from IR and PMR spectroscopy it was concluded that the synthesized compounds exist in the oxime form. Their acid ionization constants were determined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1101–1105, August, 1980.     

聚(乙烯基对苯二甲酸二烷基酯)的非寻常相转变

以聚(乙烯基对苯二甲酸二烷基酯)(PDAVT)为对象,用热分析、X射线衍射、流变及固体核磁共振等方法考察了甲壳型液晶高分子中存在的"低温无序、高温有序"的非寻常相行为.实验证明,在升温过程中,烷基基团为丁基、己基和辛基的PDAVT(P4、P6和P8)可从无定形态发育出柱状(Col)液晶相,导致在高温区体系模量升高.降温时P6和P8可完全回到无定形态,表现出典型的"各向同性相重入"行为.PDAVT液晶相畴的生长具有一维生长的特点,是成核控制的,升高温度可加快Col相的形成.固体核磁共振实验表明,样品从无定形态转变为Col相的过程与侧链运动性的不断加强有密切关系.我们也初步探索了剪切场或拉伸场对液晶转变的影响,发现当温度不高时,剪切或拉伸既不改变液晶转变温度,也没有提高液晶态样品的液晶化程度.综合分析多方面的实验结果可以看出,PDAVT的非寻常相行为是熵主导的.侧链的加速运动会增强"甲壳效应",Col相是侧链熵最大化的结果.     

The fragmentation of some alkyl thio-phosphate esters by electron-impact

The mass spectra of the following compounds have been studied: and the fragmentation pathways established with the aid of accurate mass measurements, metastable transition and appearance potential determination. The mass spectra show that the sulphur-containing compounds (II to IV) give a stronger molecular ion that that of compound I. A further significant difference is the low intensity, in the mass spectra of II to IV, of the fragments relative to the processes that occur in I, probably because the electron removed upon ionisation belongs to the sulpher atom in compounds II to IV and to the oxygen in compound I. The isomeric compounds, (III and IV) show quite different mass spectra, The radicals containing only Phosphorus and oxygen have an ionisation potential close to 9 eV and the presence of sulphur considerably lowes this value. The measured ionisation potentials of compounds I to IV are respectively, 10·7₀, 9·5₅, 9·2₀ and 9·0₀eV. The heats of formation of compounds II and III have been estimated as ?176 and ?118 Kcal mole^?1, respectively.     

The mass spectra of some alkyl and aryl imidazolines

The mass spectra of mono- and di-substituted alkyl and aryl imidazolines have been measured and the spectra analysed with the aid of deuterium labelling and high resolution techiques. In contrast to the fragmentation of thiazolines, all principal fragments of the imidazoline ring contain one nitrogen with or without hydrogen migration. In the case of 2,4-disubstituted imidazolines, the presence of two tautomeric molecular ions are suggested.