Correlations between topological features and physicochemical properties of molecules

The article reviews in brief, thede novo group additivity approach and, at length, the different topological approaches to obtain predictive and internally consistent correlations between various properties and structural features of molecules. The stress has mainly been on the molecular connectivity method. A new rational scheme for nomenclature of connectivity indices of different orders and types is introduced. The concept of the perturbation connectivity parameter developed by us recently has been applied to obtain correlations for molar refraction, boiling point, molar volume, heat of atomisation, heat of combustion, heat of vaporisation, magnetic susceptibility and critical constants of alkanes, alcohols and alkylbenzenes. A comparative study of various approaches reveals that the present perturbation topological approach has an edge over other similar methods.     

Collection and Identification of Trace Organic Compounds in Atmospheric Deposition from a Semi-Rural Site in the U.K.

Abstract

The collection of rainwater, aerosol and vapour samples at a semi-rural site in the UK was achieved using a PTFE-lined wet-only rainfall collector and a high-volume filter/adsorption trap air sampler, respectively. Analysis of atmospheric deposition revealed the presence of several hundred compounds, many of which were of anthropogenic origin, e.g.: PAH, phenols and alkylbenzenes. Amounts of compounds varied from low nanograms to tens of micrograms per litre in rainwater samples and from low picograms to high nanograms per cubic metre in aerosols. Phenolic compounds were the most abundant group of organics identified in rainwater and were present at total concentrations of >20μg1^?1 in some of the samples analysed. In the high-volume air samples most anthropogenic compounds were detected in the adsorbent rather than the filter extract. Seasonal variations in the PAH content of the adsorbent extracts were observed. The presence of siloxanes in the air samples was thought to be the result of contamination.     

Magnetic suspectibilities of liquid gold alloys

Abstract

The temperature dependences of the magnetic susceptibilities of liquid Au-Zn and Au-Cd alloys have been measured. Curves of the susceptibilities of these alloys for all concentrations show rather a big deviation from the linearly interpolated ones. With the increase of temperature, these curves approach the interpolated curves. This fact might be related to the change of clustering in the liquid state, which approaches a random mixture with the increase in temperature.     

Enantiomer separation of side-chain fluorinated alkylbenzenes by capillary gas chromatography on cyclodextrin phases

Summary The separation of racemic side-chain fluorinated alkylbenzenes and bromofluorinated analogues by capillary gas chromatography using permethylated , and -cyclodextrins dissolved in polysiloxanes of different polarity as stationary phases is described. The influence of the achiral polysiloxane matrices on the separation of enantiomers is discussed in the light of the results obtained with the different phases. For a part of the tested compounds thermodynamic data are determined which describe the interaction of enantiomers with the stationary phase. The mechanism of separation is discussed on this basis and by comparison with data for structurally similar compounds.     

Stability Constants for 1:1 Complexes Formed between2-hydroxypropyl-β-Cyclodextrin with an Average Substitution Degree of 4.4 and Benzene and Alkylbenzenes as Guests by Modified Static Head-Space Gas Chromatography Method

Modified static head-space gas chromatography method (M-SHSGC method) was used to determine the stability constants of benzene and alkylbenzenes with 2-hydroxypropyl-β-cyclodextrin inclusion complexes. The 1:1 stability constants were in agreement with those obtained by conventional SHSGC method. The M-SHSGC method precludes the necessity of the calibration curve by the use of Henry’s law constant of guest. Consequently, it is more advantageous than conventional SHSGC method because the time required to determine the stability constant is markedly reduced.     

2,7-dimethyl-3,8-dinitrodipyrazolo[1,5-a:1',5'-d]pyrazine-4,9-dione: a new labelling reagent for liquid chromatographic analysis of amino acids

Linear alkylbenzenes (LABs) are discharged into the environment as sub-products of linear alkylbenzenesulfonate (LAS) detergent. Their association with LAS is attributed to the incomplete sulfonation of the LABs in detergent manufacturing resulting in products having LAB. Recently there has been widespread interest in their use as markers of sewage effluent in the aquatic environment. Although LABs may be potentially useful in assessing the distribution and degradation of domestic wastewater, studies about it are still limited probably due to the analytical difficulties.In this article, a new analytical method for the determination of LABs in detergents using gas chromatography coupled to mass spectrometry (GC-MS) in combination with solid phase microextraction (SPME) is proposed. This alternative sample preparation technology presents several advantages, since it is solvent free, fast, uses the whole sample for analysis, requires only small amounts of sample and the fibers for the extraction procedure are reusable. A factorial experimental design was utilized to obtain the optimum values for the main operational parameters in the analysis of LABs in detergents using direct SPME in the pre-concentration step.     

Excess molar volumes of 2-methylethylbenzene with benzene,methylbenzene or ethylbenzene at various temperatures

Excess molar volumes of benzene or methylbenzene + 2-methylethylbenzene at 25, 35 and 45°C and of ethylbenzene + 2-methylethylbenzene at 25°C have been determined from density measurements using a vibrating tube densimeter. Experimental V _m ^E values have been compared with calculated values based on the Flory theory.List of Symbols p _i characteristic pressure of pure component - reduced temperature of pure component - V ^E excess molar volume - V _i ^* characteristic volume of pure component - reduced volume of mixture - reduced volume of pure component i - X ₁₂ interaction parameter in Flory's theory - site fraction of component 2 - segment fraction of component 2     

Electrochemical cleavage of a benzylic C-C bond in arylaliphatic compounds

Electrochemical cleavage of a benzylic C-C bond in arylaliphatic compounds and the effect of the structure of their alkyl and aryl fragments on the process are studied. Cleavage was found to be the most effective for substituted benzenes and anisoles with side chains bearing vicinal methoxy- and hydroxy-groups in the a- and -positions. Cleavage was moderate for cior -methoxy(hydroxy)- and (,-dialkoxyalkyl)arenes. Electrolysis carried out in methanol results in formation of PhCH₂OMe and PhCH(OMe)₂ from PhCH₂R and PhCH(OMe)R, benzaldehyde from (1,2-dihydroxypropyl)benzene, acetophenone from 2-phenylhexan-2-ol, 4-MeOC₆H₄CH(OMe)₂ from 4-(1,2-dimethoxypropyl)anisole, and 2-(MeO)₂CHC₆H₄CH(OMe)₂ from 1,2-dimethoxyindan.Translated fromIzvestiya Akademii Nauk, Seriya KMmicheskaya, No. 1, pp. 140–143, January, 1993.     

烷基苯上5-H溴代反应新方法的研究(Ⅰ)

研究了一种新的烷基苯上 α-H的溴化方法 ,发现使用 KBr O3/Na HSO3作为溴化剂 ,对系列烷基苯 ,尤其是有第二类取代基存在的烷基苯 ,在较低温度 ( 50℃～ 55℃ )及白炽光照射等溴化工艺条件下 ,能获得纯度较好 ,收率较高的α-溴代烷基苯衍生物。该新方法反应条件温和、操作简便、溴的利用率高、无腐蚀性气体 HBr产生