Polar substituent effects in the bicyclo[1.1.1]pentane ring system: acidities of 3-substituted bicyclo[1.1.1]pentane-1-carboxylic acids

Experimental gas-phase acidities are reported for a series of 3-substituted (X) bicyclo [1.1.1]pent-1-yl carboxylic acids (1, Y = COOH). A comparison with available calculated data (MP2/6-311++G**// B3LYP/6-311+G**) reveals good agreement. The relative substituent effects are shown to be adequately described by a much lower level of theory (B3LYP/6-31+G*). Various correlations are presented which clearly point to polar field effects as being the origin of the relative acidities.     

A comparative investigation of the fatty acid compositions of the seeds of a number of lines of a genetic collection of Gossypium hirsutum

A comparative analysis has been made of the amounts of lipids and their fatty-acid compositions in the seeds of the lines of agenetic collection of cotton plants of the speciesGossypium hirsutum and their hybrids and the variety Tashkent-1. The results obtained on the fatty-acid compositions of some hybrids make it possible to recommend the use of individual lines of cotton plants as donors for improving the food-value indices of cottonseed oil.Institute of Chemsitry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 173–176, March–April, 1991.     

高能核碰撞中带电多重数快度与能量和中心度的关系

用强子–弦级联模型JPCIAE及相应的Monte Carlo事例产生器研究相对论性核–核碰撞中带电粒子多重数的赝快度密度对能量和中心度的依赖关系.无需另调任何模型参数的条件下,此模型可以同时较好地描述相对论性pp实验数据及PHOBOS和PHENIX实验组的Au+Au实验数据.本文指出:因〈N_part〉并非严格定义的物理量,致使实验上和理论上确定〈N_part〉有一定任意性,从而使得每参加者核子对的带电粒子赝快度密度随着〈N_part〉的增加可能逐渐增大,也可能逐渐减小,因此用它来区分粒子产生机制是欠妥的.     

Acidic potassium permanganate as a chemiluminescence reagent--a review

A critical and comprehensive review of acidic potassium permanganate chemiluminescence is presented. This includes discussion on reaction conditions, the influence of enhancers such as polyphosphates, formaldehyde and sulfite, the relationship between analyte structure and chemiluminescence intensity, and the application of this chemistry to determine a wide variety of compounds, such as pharmaceuticals, biomolecules, antioxidants, illicit drugs, pesticides and pollutants. Previous proposals for the nature of the emitting species are re-evaluated in light of recent evidence.     

Diastereofacial selectivity in some 4‐substituted (X) 2‐adamantyl derivatives: electronic versus steric effects

π‐Facial selectivity data for the reduction and methylation of some 4^ax‐substituted (X) 2‐adamantanones ( 3 , Y = O) as well as the nucleophilic trapping of secondary and tertiary 4^ax‐substituted (X)‐2‐adamantyl cations ( 4 ; R = H and CH₃, respectively) and the 4‐methylene‐2‐adamantyl radical ( 8 ) are presented. The pronounced anti‐face selectivities observed for ( 3 , Y = O and 4 , R = CH₃) emphasize the importance of the steric factor as expected for systems with a strong steric bias. However, the dominant syn‐face capture of 4 (R = H) was completely unexpected and highlights a subtle interplay between steric and electronic effects. Finally, the very high anti‐face stereoselectivity for the trapping of ( 8 ) with the trimethylstannyl anion (Me₃Sn^?) is rationalized in terms of an electrostatic effect overwhelming the steric factor. Copyright © 2007 John Wiley & Sons, Ltd.     

Carbon-13 substituent chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl cyanides

The carbon-13 substituent chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl cyanides are a linear function of the substituent inductive parameters.     

The importance of chain length for the polyphosphate enhancement of acidic potassium permanganate chemiluminescence

Sodium polyphosphate is commonly used to enhance chemiluminescence reactions with acidic potassium permanganate through a dual enhancement mechanism, but commercially available polyphosphates vary greatly in composition. We have examined the influence of polyphosphate composition and concentration on both the dual enhancement mechanism of chemiluminescence intensity and the stability of the reagent under analytically useful conditions. The average chain length (n) provides a convenient characterisation, but materials with similar values can exhibit markedly different distributions of phosphate oligomers. There is a minimum polyphosphate chain length (∼6) required for a large enhancement of the emission intensity, but no further advantage was obtained using polyphosphate materials with much longer average chain lengths. Providing there is a sufficient average chain length, the optimum concentration of polyphosphate is dependent on the analyte and in some cases, may be lower than the quantities previously used in routine detection. However, the concentration of polyphosphate should not be lowered in permanganate reagents that have been partially reduced to form high concentrations of the key manganese(III) co-reactant, as this intermediate needs to be stabilised to prevent formation of insoluble manganese(IV).     

Determination of selected neurotransmitter metabolites using monolithic column chromatography coupled with chemiluminescence detection

The oxidation of selected clinically important neurotransmitter metabolites with acidic potassium permanganate in the presence of polyphosphates evokes chemiluminescence of sufficient intensity to enable the sensitive determination of these species. Limits of detection for 5-hydroxyindole-3-acetic acid (5-HIAA), vanilmandelic acid (VMA; α,4-dihydroxy-3-methoxybenzeneacetic acid), 4-hydroxy-3-methoxyphenylglycol (MHPG), homovanillic acid (HVA, 4-hydroxy-3-methoxyphenylacetic acid) and 3,4-dihydroxyphenylacetic acid (DOPAC) were between 5 × 10⁻⁹ and 4 × 10⁻⁸ M, using flow-injection analysis methodology. In addition, we demonstrate the rapid determination of homovanillic acid and 5-hydroxyindole-3-acetic acid in human urine - without the need for extraction procedures - using monolithic column chromatography with chemiluminescence detection.     

Metalloidalmethyl substituent effects by 13C and 19F NMR : electron release in the neutral ground state.

¹³C and ¹⁹F chemical shift studies of a series of CH₂M(CH₃)₃ and CH₂M(C₆H₅)₃ (M  Si, Ge, Sn, Pb) - substituted aryl derivatives (phenyl; 1-naphthyl; 2-naphthyl) have established unambiguously that the order of hyperconjugative electron release in the neutral ground state is Pb>Sn>Ge>Si. This order is clearly at variance with the commonly accepted order(Pb>Sn>Ge>Si) based on studies of electron deficient substrates. The phenomenon is discussed in terms of current theories on σ-π interactions. In addition, substituent parameters (σ_I and σ_R^o) for the PB(CH₃)₃ group have been derived utilizing new data from the fluorophenyl tag. These new constants are compared with those previously reported.     

Exploration for Degradation of Λ Polarization Produced in Relativistic Nucleus Nucleus Collisions

The degradation of Λ transverse polarization produced in S+Pb central collisions at energy 200 GeV per nucleon has been studied in detail. The S+Pb central collision events have been generated using Monte-Carlo generator——LUCIAE at 200 GeV per nucleon. The various factors degrading Λ transverse polarization have been analysed quantitatively. The ratios of Λ′s produced from rescattering, secondary production and decays of Σ, Ξ hyperons to the total measurable Λ′s in experiment have been investigeted and the degradation effect of these Λ on the total polarization has been determined. The simulation and calculation show that above three factors decrease the Λ transverse polarization strongly, however, can not eliminate the polarization completely when the Λ′s are assumed to be produced from hadronic gas in the final state. To explan the experimental data of vanished Λ polarization, it probably needs to consider new mechanisms of Λ production, including a weak effect of QGP formation.