Synthesis of 1,3-diarylacetones from N-(arylacetyl)benzotriazoles via arylketene intermediates

Several 1-acylbenzotriazoles were synthesized and treated with sodium hydride to afford symmetrical ketones via the dimerization of intermediate ketenes followed by hydrolysis and the loss of carbon dioxide. © 1996 John Wiley & Sons, Inc.     

Hammett analysis of a family of carbene-carbene complex equilibria

p-X-substituted phenylchlorocarbenes (X = NO(2), CF(3), Cl, H, Me, and MeO) form π-type complexes with trimethoxybenzene in pentane. The carbenes and complexes are in equilibrium, and logarithms of the measured equilibrium constants are well correlated by Hammett σ(p) constants with ρ = 2.48. The carbene complexes are characterized by UV-vis spectroscopy, and computational analysis is afforded by DFT calculations.     

Two-photon induced photodecarbonylation reaction of cyclopropenones

Irradiation of cyclopropenones (1a-c) with 800 nm pulses of ultrafast laser results in a photodecarbonylation reaction via nonresonant two-photon absorption of light.     

Trap phosphorescence spectra and lifetimes from crystalline tetramethylcyclobutane-1,3-dithione

Phosphorescence spectra and lifetimes of single crystal tetramethylcyclobutane-1,3-dithione (TMCBDT) have been measured over the temperature range 1.6–30 K. Analysis of the phosphorescence intensities as a function of temperature shows that the emission originates from a series of defect traps. At low-temperature emission is observed from the individual triplet spin sublevels of a deep-lying trap. The influence of spin-lattice relaxation on the decay from this trap is modelled. Highly selective intersystem crossing into two of the triplet sublevels is shown to occur. First-order spin-orbit coupling of various excited singlets to two sublevels of the emissive ³A_u state is suggested as the primary mechanism for S-T intersystem crossing. Evidence is presented that the deepest trap is a thio-dione impurity, probably TMTCBD (tetramethyl-3-thio-1,3-cyclobutanedione).     

Hammett studies of aryldichloromethide carbanion reactions

[reaction: see text] Rate constants were measured for the capture of para-substituted phenylchlorocarbenes by chloride ions to form aryldichloromethide carbanions and for the additions of these carbanions to acrylonitrile. Hammett analyses give rho = +0.86 for the former reaction and rho = -2.65 for the latter reaction.     

Pi-stacking interactions in some crystalline cisoid E,E-1,4-diaryl-1,3-butadienes

A cisoid E,E-1,4-diperfluorophenyl-1,3-butadiene has been prepared in which offset stacking between perfluorophenyl-perfluorophenyl rings occurs, and face-to-face stacking between phenyl-perfluorophenyl rings is found in crystals of its 1:1 complex with a cisoid E,E-1,4-diphenyl-1,3-butadiene.     

New side chain liquid crystalline polysiloxanes containing 1,3-dithiane or 1,3-dioxane rings as mesogenic side groups

New liquid crystal materials: 2-\[p-(9-decenyloxy)phenyl]-5-(p -alkoxyphenyl)-1,3-dioxane( 11 ) and 2-\[p-(9-decenyloxy)phenyl]-5-(p -alkoxyphenyl)-1,3-dithiane( 12 ) were synthesized. The mesomorphic behaviour of these compounds was determined. Though the 1,3-dioxane-type monomer exhibited both SmA and nematic phases, the 1,3-dithiane-type monomer only exhibited a nematic phase. By the hydrosilylation of poly(methylhydrosiloxane) and these monomers, side chain polysiloxanes were synthesized. For the monomers, the transition temperatures of the nematic to isotropic transitions of 1,3-dioxane-type compounds are higher than those of the corresponding 1,3-dithiane-type compounds. However, in the polysiloxane polymer this relation reversed.     

Hammett correlations in the chemistry of 3-phenylpropyl radicals

The energetics and kinetics of the reaction of variously substituted benzyl radicals with a model alkene were calculated at the G3(MP2)-RAD//B3-LYP/6-31G(d) level of theory to determine whether such reactions are amenable to Hammett analysis. The reactions were studied both in the gas phase and in toluene solution in the temperature range 298-353 K; calculations include 1D-hindered rotor corrections for low frequency torsional modes, and the solvation energies were calculated using COSMO-RS at the BP/TZP level of theory. The addition reaction was found to be dominated by radical stabilization effects, but under circumstances where olefin substituent effects were decoupled from aryl substituent effects, a modest polar effect comes into play, which is enhanced by solvation. Reasonable correlations with empirical substituent parameters such as Hammett σ and σ(?) are observed for the enthalpy of activation, but additional entropic factors act to decrease the degree of correlation with respect to free energies and rate coefficients, confirming hypotheses from earlier experimental work. Substituent effects on the reverse β-fragmentation reaction, and potential cyclization of the 3-phenylpropyl radicals formed by addition are also discussed.     

Kinetic studies of the laser-induced photodecarbonylation of 3,5-di-tert-butyl-1,2-benzoquinone

The photodecarbonylation of 3,5-di-tert-butyl-1,2-benzoquinone was initiated by excitation of the ¹(π−π*) and the ¹(n−π*) state, respectively, with the use of emission lines of an argon ion laser. The UV—vis reaction spectra exhibit a strong sensitivity to the selected solvents. Both UV—vis spectra and MR spectra show the existence of a persistent bis-ketene intermediate. The kinetic analysis yields that the course of reaction can be described as a consecutive process. The primary step acts as a light-induced electrocyclic ring cleavage generating the intermediate. In the second step, the CO abstraction leads to the corresponding monoketone.     

Comparative conformational analysis of 1,3-dioxane and 1,3-dithiane

It was shown by ab initio quantum-chemical approximations HF/6-31G(d) and MP2/6-31G(d)//HF/6-31G(d) that the conformational isomerization of 1,3-dioxane and 1,3-dithiane proceeded along common routes. The potential energy surface of both compounds contains six minima including the chair invertomers and enantiomeric flexible forms. They are separated by several potential barriers. It was established by molecular dynamics method that the flexible conformers at heating and keeping at 295–300 K transformed into each other and in the chair conformer.     

金属卟啉催化下环己烷羟基化反应中的Hammett关系

合成了40个卟啉环上具有不同取代基的单铁、锰卟啉和u-氧桥连双铁、锰卟啉,研究了这些金属卟啉模拟细胞色素P－450单充氧酶在温和条件下催化环己烷羟基化的反应.首次用线性自由能关系对金属卟啉仿生催化反应和金属卟啉自氧化反应进行相关分析,获得一些新的结果和规律.在此基础上,对金属卟啉仿生催化反应的可能机理进行了探讨.     

Side-chain liquid crystalline polyesters derived from diethylmalonate and/or 1,3-propanediol

A series of azo monomers for polycondensation have been synthesized and characterized. These monomers, which contain electron-donor or acceptor substituents, have been condensed with aliphatic monomers to obtain two different series of aliphatic main-chain polyesters with pendant mesogenic groups. The polymers display nematic or smectic phases depending on the structural modifications of pendant mesogenic groups and the length of the flexible main-chain. In addition to these series, two polyesters with a high concentration of side pro-mesogenic groups have been synthesized. © 1996 John Wiley & Sons, Inc.     

Liquid crystalline polymers containing heterocycloalkane mesogens. 2. Side-chain liquid crystalline polysiloxanes containing 2,5-disubstituted-1,3-dioxane mesogens

Polysiloxanes and copolysiloxanes containing 2-(p-hydroxyphenyl)-5-(p-methoxyphenyl)-1,3-dioxane and 5-(p-methoxyphenyl)-1,3-dioxan-2-yl as mesogenic units and an aliphatic spacer containing 11 and 10 methylene units, respectively, were synthesized. Their phase behavior was studied by differential scanning calorimetry and optical polarization microscopy, and compared with the phase behavior of the polysiloxanes and copolysiloxanes containing 4-methoxy-4′-hydroxybiphenyl and 4-cyano-4′-hydroxybiphenyl mesogens attached to the polymer backbone through an aliphatic spacer containing 11 methylene units. All synthesized polymers present smectic mesomorphism. The polymers containing 4-methoxy-4′-hydroxybiphenyl and 4-cyano-4′-hydroxybiphenyl are also crystalline, while the polymers containing 1,3-dioxane based mesogens do not crystallize.     

Impurity analysis in pure-grade 1,3-butadiene

Summary The separation of 20 impurities in a pure-grade 1,3-butadiene has been carried out at 46°C by using Carbopack B modified with 4.94% picric acid.     

Conformational analysis of 1,3-dioxane in nanotubes

Russian Journal of Organic Chemistry - Computer simulation of conformational transformations of 1,3-dioxane molecule within model single-walled carbon nanotubes (hybrid DFT-method PBE/3ζ)...     

Electron spectra of Hammett dye-indicators sorbed by montmorillonite

Theoretical and Experimental Chemistry -     

Conformational analysis of 1,3-oxathiane

Computer simulation of pathways of conformational isomerization of 1,3-oxathiane molecule carried out with the help of HF/6-31G(d), MP2.6-31G(d)/HF/6-31G(d), and PNE/3z quantum-chemical approximations showed that interconversion between the degenerate in energy chair conformers proceeds through seven independent pathways: directly and via six flexible forms. Potential energy surface contains eight minimum points including chair conformers and enantiomeric pairs of twist forms, and also five transition states, among them different modification of semi-chair, symmetric and unmmetrical boat. Molecular dynamics methods show that flexible forms at room temperature convert into one another and into the chair conformers.     

Hammett rho of reactions of MeLi with benzophenones

Relative rates of reactions of MeLi with benzophenones in diethyl ether at 0 degrees C that furnish methyldiarylmethanols were determined using slow addition of a MeLi solution to solutions containing an excess of two benzophenones. The additions exhibit a Hammett rho of 0.94.     

丙烯醛光致脱羰机理的量子化学研究

用量子化学方法研究了丙烯醛基态和激发态的反应途径, 通过比较不同反应途径的反应势垒和中间产物构型的稳定性, 从理论上得出该反应的反应机理。