无限长氢链极化率的从头算研究

在RHF／6-31G水平用CPHF方法计算了两种构型的氢链的轴向极化率,计算直到89个结构单元,已基本上达到每单元极化率的极限值。根据这些较完整的资料,讨论了拟合目标函数的选取,拟合函数的确定,以及如何选定拟合数据范围以求得最佳极限值的问题,提出了求得最可信的每单元极化率极限值的原则。     

Sensitive new test for aliphatic,aromatic, and heterocyclic aldehydes

Summary A new sensitive spot test for aliphatic, aromatic and heterocyclic aldehydes is introduced. Limits of identification for over 70 aldehydes are recorded. All tested aldehydes except chloral and hexadecanal give positive tests revealed by a blue or a green color with an absorption maximum around 610 to 630 nm (m). For the determination of total aldehyde, the procedure is at best an estimation.

---

Zusammenfassung Eine neue Tüpfelprobe für aliphatische, aromatische und heterocyklische Aldehyde wird vorgeschlagen. Die Erfassungsgrenzen für mehr als 70 Aldehyde werden angegeben. Mit Ausnahme von Chloral und Hexadekanal geben alle geprüften Aldehyde eine blaue bis grüne Färbung mit einem Maximum der Absorption bei 610 bis 630 nm. Eine kolorimetrische Bestimmung des Gesamtaldehyds kann nur mit einer relativen Präzision von etwa ±0,1 ausgeführt werden.

---

Résumé Introduction d'un nouvel essai à la touche sensible pour les aldehydes aliphatiques, aromatiques et hétérocycliques. Les auteurs donnent les limites d'identification pour plus de 70 aldehydes. Tous les aldehydes essayés donnent des essais positifs à l'exception du chloral et de l'hexadecanal; cet essai se traduit par l'apparition d'une couleur bleue ou verte ayant un maximum d'absorption au voisinage de 610 à 630 nm. Pour la détermination de l'aldéhyde total la technique peut être considérée au mieux comme une estimation.

     

Calculated polarizabilities for some aliphatic and aromatic hydrocarbons

Ground-state molecular polarizabilities of some aliphatic and aromatic hydrocarbons have been calculated using the method of Marchese and Jaffé. The polarizability components for the typical normal alkane n-heptane are found to be very nearly independent of conformation; those for biphenyl show a significant dependence but the average polarizability is approximately constant. The polarizabilities of the n-alkanes in general are seriously underestimated, but relatively good agreement with experiment is obtained for benzene and biphenyl.     

Cyclophanes as hosts for aromatic and aliphatic guests

A series of water-soluble cyclophanes, made by connecting two diarylmethane units and two bridging chains via four nitrogens, were found to provide hydrophobic cavities of definite shape and size for forming inclusion complexes with various organic compounds in aqueous solution. Some chemical modifications of these cyclophanes are described.This paper is dedicated to Professor D. J. Cram to celebrate his honor in receiving the 1987 Nobel Prize in Chemistry.     

Biodegradation of aliphatic and aromatic polycarbonates

Polycarbonate is one of the most widely used engineering plastics because of its superior physical, chemical, and mechanical properties. Understanding the biodegradation of this polymer is of great importance to answer the increasing problems in waste management of this polymer. Aliphatic polycarbonates are known to biodegrade either through the action of pure enzymes or by bacterial whole cells. Very little information is available that deals with the biodegradation of aromatic polycarbonates. Biodegradation is governed by different factors that include polymer characteristics, type of organism, and nature of pretreatment. The polymer characteristics such as its mobility, tacticity, crystallinity, molecular weight, the type of functional groups and substituents present in its structure, and plasticizers or additives added to the polymer all play an important role in its degradation. The carbonate bond in aliphatic polycarbonates is facile and hence this polymer is easily biodegradable. On the other hand, bisphenol A polycarbonate contains benzene rings and quaternary carbon atoms which form bulky and stiff chains that enhance rigidity. Even though this polycarbonate is amorphous in nature because of considerable free volume, it is non-biodegradable since the carbonate bond is inaccessible to enzymes because of the presence of bulky phenyl groups on either side. In order to facilitate the biodegradation of polymers few pretreatment techniques which include photo-oxidation, gamma-irradiation, or use of chemicals have been tested. Addition of biosurfactants to improve the interaction between the polymer and the microorganisms, and blending with natural or synthetic polymers that degrade easily, can also enhance the biodegradation.     

Biocatalytic racemization of aliphatic, arylaliphatic, and aromatic alpha-hydroxycarboxylic acids

[reaction: see text] Biocatalytic racemization of a range of aliphatic, (aryl)aliphatic, and aromatic alpha-hydroxycarboxylic acids was accomplished by using whole resting cells of a range of Lactobacillus spp. The mild (physiological) reaction conditions ensured an essentially "clean" isomerization in the absence of side reactions, such as elimination or decomposition. Whereas straight-chain aliphatic 2-hydroxycarboxylic acids were racemized with excellent rates (up to 85% relative to lactate), steric hindrance was observed for branched-chain analogues. Good rates were observed for aryl-alkyl derivatives, such as 3-phenyllactic acid (up to 59%) and 4-phenyl-2-hydroxybutanoic acid (up to 47%). In addition, also mandelate and its o-chloro analogue were accepted at a fair rate (45%). This biocatalytic racemization represents an important tool for the deracemization of a number of pharmaceutically important building blocks.     

Reactions of aliphatic,aromatic, and heterocyclic aminothiols with diacetylene

Reactions of aliphatic, aromatic, and heterocyclic aminothiols with diacetylene in liquid ammonia or methanol furnished the corresponding aminoorganylsulfanylbutenynes of predominantly Z-configuration.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 11, 2004, pp. 1725–1727.Original Russian Text Copyright © 2004 by Volkov, Volkova.     

A versatile Ru catalyst for the asymmetric transfer hydrogenation of both aromatic and aliphatic sulfinylimines

A highly efficient Ru catalyst based on an achiral, very simple, and inexpensive amino alcohol ligand (2‐amino‐2‐methylpropan‐1‐ol) has been developed for the asymmetric transfer hydrogenation (ATH) of chiral N‐(tert‐butylsulfinyl)imines. This complex is able to catalyze the ATH of both aromatic and the most challenging aliphatic sulfinylimines by using isopropyl alcohol as the hydrogen source. The diastereoselective reduction of aromatic, heteroaromatic, and aliphatic sulfinylketimines, including sterically congested cases, over short reaction times (1–4 h), followed by desulfinylation of the nitrogen atom, affords the corresponding highly enantiomerically enriched (ee up to >99 %) α‐branched primary amines in excellent yields. The same ligand was equally effective for the synthesis of both (R)‐ and (S)‐amines by using the appropriate absolute configuration in the iminic substrate. DFT mechanistic studies show that the hydrogen‐transfer process is stepwise. Moreover, the origin of the diastereoselectivity has been rationalized.     

分子极化效应指数与脂肪族醛酮的沸点

建立物质的定量结构—活性相关性(QSAR)和定量结构—性质相关性(QSPR)的研究一直受到化学工作者的关注。用拓扑指数研究饱和烃的各种物理化学性质已经有大量报道1 4。本文讨论了分子极化效应指数[5]与脂肪族醛酮沸点的关系,力求寻找到一个适用范围广,并且具有分子结构特征的计算脂肪族醛酮沸点的计算公式。1　分子结构参数的确定脂肪族醛酮分子中羰基的存在,使相同碳原子数的醛酮沸点比烷烃升高很多。我们以醛酮分子中的烷基极化效应指数(PEI)的差值(ΔPEI)[6]来表示羰基位置对醛酮沸点的影响:ΔPEI=PEIB,N-PEInrm,N(1)式中,…     

Modification of the static polarizability by a perfect metallic surface

We calculate the modifications of the static polarizability of a general system (atom or molecule) induced by a perfect metallic surface. The calculations use the Feynman propagator and take retardation effects into account. For any distance from the mirror the induced polarizability is composed of two terms: a classical one without retardation and a quantum one which is always retarded. Two limiting cases are then considered: the Casimir limit where the classical term dominates and the near-zone limit (London limit) where the quantum correction must be added to the classical term.     

Stability and reactivity of all-metal aromatic and antiaromatic systems in light of the principles of maximum hardness and minimum polarizability

It is demonstrated that among various possible isomers of all-metal aromatic compounds such as Al(4)(2-) and their complexes the most stable isomer with the minimum energy is the hardest and the least polarizable. A similar situation is observed for different isomers of all-metal antiaromatic compounds such as Al(4)(4-) and their complexes. It is shown that linear Al(4)(4-) is energetically more stable than its cyclic isomer. The reaction energies associated with the complexation processes highlight the stability of those complexes. The difference in energy, hardness, and polarizability between a cyclic molecule and its linear counterpart convincingly shows that an aromatic molecule exhibits negative changes in energy and polarizability but positive changes in hardness as expected from the principles of minimum energy, minimum polarizability, and maximum hardness. Although the aromaticity of Al(4)(2-) is unequivocally established through this study, the antiaromaticity picture in the case of Al(4)(4-) is shown to be poorly understood;however, the present analysis sheds light on this controversy.     

A thermodynamic model for the shape and stability of twinned nanostructures

Although thermodynamically metastable, planar defects are often observed in many faceted nanomaterials including nanocrystals, nanorods, and nanowires, even after annealing. These planar defects include contact twins and (intrinsic or extrinsic) stacking faults, and are usually neglected by most analytical models. For example, many bulk metals have the face-centered cubic structure, but small nanocrystals and nanorods of the same material often exhibit various structural and morphological modifications such as single or multiple symmetric twinning, as well as 5-fold cyclic twinning resulting in decahedral and truncated decahedral nanostructures. Presented here is a general analytical model for the investigation of nanomaterials of arbitrary shape, and with any configuration of planar defects. The model is tested for the case of twinning in unsupported gold nanocrystals and nanorods, and is shown to give results in excellent agreement with experimental and computational studies reported in the literature.     

Cyano-containing ionic liquids for the extraction of aromatic hydrocarbons from an aromatic/aliphatic mixture

Ionic liquids can replace conventional solvents in aromatic/aliphatic extractions, if they have higher aromatic distribution coef- ficients and higher or similar aromatic/aliphatic selectivities. Also physical properties, such as density and viscosity, must be taken into account if a solvent is applied in an industrial extraction process. Cyano-containing ionic liquids have a lower den- sity than the benchmark solvent sulfolane and a higher viscosity. Sulfolane is from a hydrodynamic point of view a better sol- vent than ionic liquids for the aromatic/aliphatic extraction. The most suitable ionic liquids for the extraction of aromatic hy- drocarbons from a mixture of aromatic and aliphatic hydrocarbons are [bmim]C(CN)3, [3-mebupy]N(CN)2, [3-mebupy]C(CN)3, [3-mebupy]B(CN)4 and [mebupyrr]B(CN)4. They have factors of 1.2-2.3 higher mass-based distribution coefficients than sul- folane and a similar or higher, up to a factor of 1.9 higher, aromatic/aliphatic selectivity than sulfolane. The IL [3-mebupy]N(CN)2 is a better extractant for the separation of toluene from a mixture of toluene/n-heptane in a pilot plant Ro- tating Disc Contactor (RDC) than sulfolane.