An Alternative Method for Anomeric Deacetylation of Per-acetylated Carbohydrates

An alternative method for anomeric deacetylation of fully acetylated carbohydrates has been developed using imidazole in methanol.     

Fugacity coefficients for water vapor

The fugacity coefficient of water vapor were calculated along the saturation line at temperatures from 273.16 to 647.14 K and at supercritical temperatures from 673.15 to 1073.15 K and pressures from 5 to 1000 MPa.     

熵函数的一种引入法

从数学上证明δQR/T可由全微分入手;结合几个常见的可逆循环过程,较为简明地介绍一种熵函数的引入法。该方法既省去了经典方法的烦琐推理,也避免了单刀直入式定义的困惑;不失热力学的严谨性,同时也有益于第一定律和第二定律的衔接。     

Introducing Alternative Algorithms for the Determination of the Distribution of Relaxation Times

Impedance spectroscopy is a powerful characterization method to evaluate the performance of electrochemical systems. However, overlapping signals in the resulting impedance spectra oftentimes cause misinterpretation of the data. The distribution of relaxation times (DRT) method overcomes this problem by transferring the impedance data from the frequency domain into the time domain, which yields DRT spectra with an increased resolution. Unfortunately, the determination of the DRT is an ill-posed problem, and appropriate mathematical regularizations become inevitable to find suitable solutions. The Tikhonov algorithm is a widespread method for computing DRT data, but it leads to unlikely spectra due to necessary boundaries. Therefore, we introduce the application of three alternative algorithms (Gold, Richardson Lucy, Sparse Spike) for the determination of stable DRT solutions and compare their performances. As the promising Sparse Spike deconvolution has a limited scope when using one single regularization parameter, we furthermore replaced the scalar regularization parameter with a vector. The resulting method is able to calculate well-resolved DRT spectra.     

Buffered Silicagel Systems - An Alternative Method for the Separation of Polar Compounds

Abstract

The adsorption chromatography of polar compounds on normal silicagel gives very often strongly tailing peaks and, therefore, poor resolution. By coating the surface of the silicagel with a buffer salt, the tailing disappears and all the advantages of adsorption chromatography can be used. On buffered silicagel, nonionic compounds behave in the same way as on the untreated adsorbent. In this paper we describe the influence of type, pH and concentration of the buffer solution used to modify the silicagel on the performance of the separation system. The changes in separation selectivity and various applications are shown.     

Electrospray Mass Spectrometry: An Alternative Method for the Identification of Organotin Compounds

The limitations of conventional gas chromatography–mass spectrometry (GC–MS) analyses for alkyl- and aryl-tin compounds are discussed, particularly the excessive fragmentation from electron impact (EI) ionization. Negative EI methods exhibit low ionization capabilities and are restricted to compounds with an electronegative centre, and are thus not suitable for general routine analysis. Liquid chromatography–MS (LC–MS) interfaces offer potential advantages in terms of reduced sample work-up since no derivatization is required. Electrospray techniques give reproducible mass spectra for each compound studied under fixed instrumental parameters. Changes in the cone/repeller voltages can radically alter the observed mass spectra. High-mass species were observed for each compound studied and tentative structures for these species are proposed.     

Fugacity Calculations Using Estimated Physicochemical Properties

Abstract

Fugacity calculations according to Mackay and Paterson have been performed for a set of 114 chemicals. Calculations using experimental input parameters and calculations based on estimated parameters are comparatively presented. It is shown that estimated parameters are useful for an estimation of environmental distribution provided the estimation methods are chosen carefully and experimental melting points as well as boiling points are available. Estimation methods for vapour pressure and water solubility need further development.     

An Improved Alternative Norgestrel Preparation

Ethynyl cerium chloride, prepared in situ from ethynyl magnesium bromide or lithium acetylide and anhydrous cerium chloride efficiently added to 13-ethyl-3-methoxy-gona-3,5-diene-17-one 2. Aqueous HCl hydrolysis of intermediate enol ether 3 gave high yields of norgestrel 4.     

An Alternative to Automatic Titration

Automatic titrators are designed to do exactly what a lab-technician used to do. Much more sophisticated automation of volumetry is possible. Omegaphoresis [3] in buffer-free [2] sample solutions automatically creates a stationary multiple component titration curve or zoned pattern with normalized concentrations of each separated species. An automatic measurement of each zone length yields their quantity. Simultaneous automatic detection of all the zones in a 10–20 component solution in less than 2 minutes, with a precision of ±2%, a required amount of the order of less than one nanomol and a resolution of ±pK < 0.01 replaces acid-base, complexometric, and certain types of redox-titrimetry. An option of the method allows identification of the components as well.     

Benzotriazole-1-carboxamidinium Tosylate: An Alternative Method for the Conversion of Amines to Guanidines

A novel, effective and convenient reagent for the conversion of amines to guanidines is presented. Various primary and secondary amines react with benzotriazole-1-carboxamidinium tosylate (1) to give the corresponding guanidines in good yields under mild conditions.     

把分子模拟法引入高分子物理实验教学

分子模拟法（也被称作计算机模拟法）是用计算机以原子水平的分子模型来模拟分子的结构与行为,进而模拟分子体系的各种物理与化学性质,它已成为一种重要的科学研究方法,并且被广泛地应用于高分子科学的研究中。     

(3＇→5＇)亚甲基缩醛连接的二聚和三聚体脱氧核苷的另法合成

3'-O-(甲硫甲基)缩醛的脱氧核苷(1)与N-碘代丁二酰亚胺(MS)和二苯基次膦酸反应得到相应的3＇-O-(二苯膦酰氧)甲基缩醛(2).在三甲基硅三氟甲磺酸酯(TMSOTf)的条件下,后者与3＇-位保护的脱氧核苷(5)缩合,得到(3＇→5＇)甲缩醛连接的二聚体d[(B1-m-B2)](m=次甲基)(6).同样的,2(B=T或B=C)与3＇-位保护的二聚体9(T-M-T或C-m-T)缩合,可得到相应的三聚体10(T-m-T-m-T,C-m-T-T和Y-m-C-m-T).     

An Alternative Route to Yomogi Alcohol

On the basis of spectral data plus results of selective partial hydrogenation, yomogi alcohol, a new artemisia-type monoterpene originally considered to have structure I,¹ was reformulated as II.² Meanwhile, Willhalm and Thomas³ and later Thomas and Pawlak⁴ reported a nonselective synthesis of II along with a study of its chemistry. Independently, Sucrow⁵ developed a specific route to II and also a synthesis of I. Here we report an efficient, alternative two-step synthesis of II starting from 3,3-dimethylpent-1-en-4-yne (III).⁶     

气体压缩因子和逸度因子的若干规律

在物理化学气体部分的教学内容中,气体的压缩因子和逸度因子均为重要概念,同时也是生产、科研和设计中的重要气体基础数据。本文通过对542种无机、有机气体的临界压缩因子数据进行整理及分析,对其数值取值范围及特点进行了讨论,同时对纯气体的压缩因子和逸度因子数值的一些简单规律进行了总结,为缺乏数据时二者的估算提供依据,以供教学参考。     

An Alternative Approach for the Synthesis of Sulfoquinovosyldiacylglycerol

Sulfoquinovosyldiacylglycerol (SQDG) is a glycolipid ubiquitously found in photosynthetically active organisms. It has attracted much attention in recent years due to its biological activities. Similarly, the increasing demand for vegan and functional foods has led to a growing interest in micronutrients such as sulfolipids and their physiological influence on human health. To study this influence, reference materials are needed for developing new analytical methods and providing enough material for model studies on the biological activity. However, the availability of these materials is limited by the difficulty to isolate and purify sulfolipids from natural sources and the unavailability of chemical standards on the market. Consequently, an alternative synthetic route for the comprehensive preparation of sulfolipids was established. Here, the synthesis of a sulfolipid with two identical saturated fatty acids is described exemplarily. The method opens possibilities for the preparation of a diverse range of interesting derivatives with different saturated and unsaturated fatty acids.     

An Alternative Method to Prepare Nitrile Oxides from Primary Nitro Compounds by Using Thionyl Chloride and Triethylamine

The dehydration of PhCH₂NO₂ (1a), PhCOCH₂NO₂ (1b), and MeOOCCH₂NO₂ (1c) with SOCl₂ in the presence of Et₃N gave three corresponding nitrile oxides. Each nitrile oxide was trapped by various dipolarophiles to obtain the cycloadducts of 2-isoxazolines.     

An Alternative Method for Correlation and Evaluation of Mutual Diffusion Coefficients of Solutes in Organic Solvents at Infinite Dilution

Based on the linear free energy relationships theory and empirical equations, correlations of mutual diffusion coefficients of solutes in organic solvents at infinite dilution at various temperatures are proposed. Four homologues in 743 binary systems have been regressed and correlation equations for the diffusion coefficients are obtained. The mean relative deviations of the four equations are 8.63%, 8.57%, 2.96%, and 4.85%, and all of the squared correlation coefficients (R²) are larger than 0.96, indicating that the fittings are good. The results reveal that a simple form of the equation exhibits high estimation accuracy, definite theory meaning, wide applicability and wide temperature range. This study successfully combines macroscopic physical properties of substances with their molecular microstructure, providing an alternative approach for calculating of mutual diffusion coefficient.     

Triflic Anhydride: An Alternative Promoter in Glycosidations

Abstract

The activation of glucosyl halides, trichloroacetimidates and of thioglucosides with triflic anhydride has been investigated showing that triflic anhydride promotes glycos idations with trichloracetimidates as well as with fluorides. There is also some potential for the activation of reactive thioglycosides. The role of triflic anhydride as a Lewis acid is likely.