New “localized orbitals” appropriate for post-Hartree—Fock calculations

In this work, we propose a new orbital set based on density matrices of subsystems. Most of the resultant orbitals are localized in the subsystems and resemble the natural orbitals of the subsystems. Correlation between two electrons, each in a distant localized orbital, should be small and the corresponding configurations can be neglected in a calculation. Test calculations are performed on hexatriene and the usefulness of these orbitals is shown. © 1996 John Wiley & Sons, Inc.     

Chemical examination of Tylophora asthmatica—II

Tylophorine has been degraded to a compound, identified as 2:3:6:7-tetramethoxy-9-methylphenanthrene. In conjunction with other degradation results and biogenetic considerations, tylophorine is now formulated as 2:3:6:7-tetramethoxyphenanthro(9:10:6′:7′)indolizidine.

A synthesis of the basic ring system, phenanthro-(9:10:6′:7′)indolizidine, present in tylophorine has been achieved.     

The bond order—bond length relationship

The difference in length between two bond orders was reported by Pauling to be essentially the same, regardless of the atoms that make up the bond. To a first approximation these differences hold not only for bond orders 1, 2 and 3 but also for six membered aromatic rings containing all carbon, carbon-nitrogen, nitrogen-nitrogen, carbon-phosphorous, carbon-arsenic, and carbon-antimony bonds. An equation was developed (based upon these differences) that relates bond order and bond length. The output of this equation was compared with those of Gordy and Pauling. Our equation as well as the Gordy equation (with revised constants) return a bond length of 1.4 Å for bond order 1.67 which is consistent with theory. (This bond order was not used in developing either the equation or the revised Gordy constants.)     

Chemical examination of Andrographis echioides—II Structure and synthesis of echioidin

On the basis of degradative and spectral evidence and synthesis, echioidin, the new flavone glucoside isolated from Andrographis echioides Nees, is shown to be 5-hydroxy-2′-β- -glucosidoxy-7-methoxyflavone (echioidinin-2′-β- -glucoside).     

Reactions of acylarylnitrosamines—II

Decomposition of acylarylnitrosamines in benzene produces not only free radicals as is well recognized, but also intermediate ion pairs. The generality of this dual mechanism is experimentally demonstrated by use of nucleophilically activated fluorine as a ‘label’. The appearance of acylfluoride in the reaction products from fluorine substituted acylarylnitrosamines is interpreted.     

Haschisch—Xi Massenspektrometrische bestimmung von haschisch-inhaltsstoffen—II

The fragmentation of cannabidiol dimethylether and related compounds has been investigated by means of deuterium labelling and model compounds. The most important fragmentation processes start with a retro-Diels-Alder reaction of the cyclohexene ring, principally witout migration of the double bond. With certain ions an unusual -cleavage of the n-pentyl and methoxy substituents of the phenyl ring has been observed.

All known double bond isomers of the tetrahydrocannabinol type have been identified with certainty by means of their mass spectra.     

Chemical Safety—An International Challenge

The protection of health and environment need to be taken into account when chemicals leave the laboratory after development to be produced in large quantities and marketed as either end or intermediate products. Over the past 20 years this necessity has led to complex structures of national and international cooperation, which are characterized by both scientific findings and political targets.     

Chemical graphs—XII Configurations of annulenes

A procedure is developed for finding out all possible configurations of annulenes (both single- and multiple-edge configurations). An exhaustive table for these geometric (cis-trans) isomers of all annulenes up to [20]annulene is presented. Every configuration is given a notation by assigning to each edge one of three possible digits indicating its direction.     

Asymmetric annellation effects—II

The comparison of the U.V. absorption spectra of acenes, 1:2–3:4-dibenzacenes and tetrabenzacenes shows a strong asymmetric annellation effect. This is explained on the basic assumption that an aromatic sextet or benzenoid ring can transfer only two electrons to another ring. Three benzenoid rings can thus produce an induced aromatic sextet in an included ring of the type of the central ring in triphenylene.

The synthesis of tetrabenzotetracene is described.     

Thermodynamique des complexes metalliques ternaires des amino-acides. II. Etude des systemes Ni(II)—glycine—valine Ni(II)—alanine—valine

Standard enthalpies and entropies of formation for binary and ternary Ni(II) complexes with pairs of the following amino acids as ligands: glycine, DL--alanine and DL-valine, were calorimetrically determined at 25°C in aqueous solution using 1 M ionic strength (NaClO₄).

The results are discussed according to every possible pathway for mixed ligand complex formation and also using the classical statistical methods. Temperature-dependent and temperature-independent components of the thermodynamic data are calculated. In all cases with these ligands involving identical coordination sites, the temperature-independent component of the enthalpy change is closely constant for binary as well as for ternary complexes. All the data show that the stabilization of mixed ligand complexes with respect to the parent binary complexes arises from the entropy term and is maximum for the Ni(II)—glycine—valine system.     

Hindered rotation in thioamides—II

The NMR spectra for a series of amides and thioamides of type where R = CH₃, C₆H₅ and C₆H₅CH₂, were investigated from ?60° to 150°C. The Arrhenius activation energies, E_a, for the normal amide equilibration were determined by the W_½ method and the values range from 15.4 to 20.9 Kcal/mole. The three thioamides, compounds ( 2 ), ( 4 ) and ( 6 ) yield spectra showing a second, low temperature, equilibration. This exchange was first studied by Siddall and co-workers and they interpreted the spectral changes in terms of population changes of the conformational isomers about the N? CH bonds. They assumed strong interaction of nitrogen alkyl groups which gave rise to three low energy dl pairs of isomers. Their results, however, as well as those obtained for similar compounds reported herein, show only two sets of patterns at low temperatures. These spectra suggest a first order, A?B, type equilibration where P_A≠P_B. An alternative assignment based upon the following classification of steric effects of S, R, R′ and R″, is suggested; (1) a strong interaction of the sulfur atom with the adjacent alkyl group on the nitrogen atom, R′, (2) a somewhat weaker interaction of R with the adjacent nitrogen alkyl group R″ and (3) a still weaker interaction of the two nitrogen alkyl groups, R′ and R″. This leads to four isomers, two dl pairs, C₁T₄, C₆T₃ and C₁T₆, C₆T₃, which are expected to have a lower energy than the rest and the first pair is preferred. The W_½ method of measuring exchange rates was extended to cover A?B equilibrations, where P_A≠P_B. The results indicate an accuracy that is not significantly lower than that obtained by the more elaborate total line shape analysis.     

Zur nomenklatur der phane—II

The new term “Phanes” has been clearly defined and a nomenclature system tentatively developed. This system is comprehensible and of general application and at the same time relatively simple. The notations “nucleus”, “bridge”, “number of bridge members” and “number of ring members” are defined. In order to get a definite characterisation of the phanes which contain a carbocyclic nucleus, a carbocyclic and heterocyclic bridge the following terms: “carbophanes”, “carba-phanes” and “hetera-phanes” have been newly introduced. The prefix “hetera-” has been proposed as a general expression and as a representative term for the syllables “aza-”, “oxa-”, “thia-” and so on. The so called “a-nomenclature” is clearly called “hetera-nomenclature”. The new expressions “heteralogous” and “substitulogous” are explained. As the various examples will show, the “Phane-Nomenclature” can also be applied to the naming of complicated metallocenophanes.     

Structural investigation of lac resin—II

The three fractions of lac rein viz., hard resin I, hard resin II and soft resin have been cleaved with hydriodic acid followed by deiodination. The products were separated into fatty acids and terpene acids. The former have been studied by GLC and data on the nature and distribution of the chain lengths and their relative amounts were thus obtained. Cleavage of the different fractions of the resin with hydrogen chloride followed by alkaline hydrolysis gave the total aleuritic acid quantitatively. Based on the above results, the possibility of the presence of alkali stable linkages in lac resin and the amount of aleuritic acid liberated only by acid cleavage have been determined.     

Image Enhancement—Chemical,Digital, Visual

Digital image processing has become well known through the high quality of some spectacular satellite images. It has developed into a discipline in its own right within information science and now finds application, not only in space travel, but also in such diverse fields as, for example, robotics, medical imaging, and television technology. Image processing also occurs, however, in photographic films and biological visual systems. In these systems, too, recorded images are manipulated for better recognition. This poses the question as to whether similar principles of image processing are operative in these different image handling systems.     

Chemical Sensors and Biosensors—Principles and Applications

Chemical and environmental engineering and biotechnology are among the fields now being transformed by continually increasing levels of automation. Whereas the objective in other sectors of industry is simply to increase efficiency, here considerations of system theory or safety demand a high level of automation. Either the processes are too complex and require multifunctional control with feedback, or an analysis of the safety requirements shows the necessity for a certain degree of redundancy in the safety measures, and for elimination of human error as a risk factor. With regard to quality control, cost-benefit analyses lead to striking conclusions which again indicate the need for highly automated, and above all reliable, systems to eliminate rejects. The crux of any automated system is the measurement and control technology; of central importance is the rapid, reliable, and in some cases continuous, measurement and interpretation of key processes or control variables. For this purpose a wide variety of recording instruments and sensors are used to give as accurate a picture as possible of the state of the system. It is obvious from this that the performance of the control system is critically dependent on the sensors. Errors in the measured quantities can become amplified in the control variables or, in dynamic systems, can lead to undesirable operating conditions. Moreover, as a consequence of great advances in microelectronics, “intelligent sensors” which can calibrate and control themselves will be one of the key technologies of the nineties. Unless fast and immediate information on the true current status of a system is available, microprocessors as control devices react blindly and unpredictably to errors in input information. New discoveries in the fields of electronic, electrochemical, and optical transducers are now being applied in heterogeneous catalysis and surface physics, and in biochemistry (enzymology and immunology); in these fields new chemical sensor principles are being tested, which could revolutionize instrumental methods of molecular analysis in particular, owing to their very favorable cost-performance relationship. This article aims to give an up-to-date overview of the current state of the art in these developments, with emphasis on their importance for analysis and their significance in relation to the chemist's interest in mechanisms for identifying substances.     

A two‐dimensional zinc(II) coordination polymer created via in situ ligand synthesis involving C—N bond formation

The novel Zn^II coordination polymer poly[{μ₄‐2‐[3‐(pyridin‐2‐yl)‐1H‐pyrazol‐3‐yl]butanedioato}zinc(II)], [Zn(C₁₂H₉N₃O₄)]_n, has been synthesized hydrothermally and structurally characterized. The results demonstrate that the complex shows two‐dimensional neutral wave‐like layers. The complex was prepared by the conjugate addition reaction of 2‐(1H‐pyrazol‐3‐yl)pyridine to cis‐fumaric acid in the presence of Zn(OAc)₂·2H₂O (OAc is acetate) at 413 K.     

Protonenresonanz-Untersuchungen an Polysaccharid-Derivaten—II: CELLULOSEDERIVATE

Cellulose derivatives are used as examples to show how NMR spectroscopy—at 100 and particularly at 220 MHz—may be applied in structural studies of polysaccharides, namely to distinguish between hexoses and pentoses, to determine the configuration and conformation of the monomer units in the polymer as well as the type of the glycosidic bond. For such investigations the acetyl, benzoyl or methyl derivatives are required. The degree of polymerization (P_w) of the acetates or methyl ethers should be P_w < 200 and in the case of benzoates P_w < 100.     

Versuche mit einem tiefgekühlten Zwillingsholkathoden-Interferometer—Spektrometer—II. Das optische System

The optical arrangement consists of a double beam imaging system an interferometer spectrometer attached to it. The two cathode spots are projected by the imaging system to the flip-flop mirror in the optical axis of the interferometer. One of the two cathode spots can be projected either to the slit of a spectroscope or to that of a spectrograph, respectively, for preliminary observation. For measuring the intensity ratios, neutral wedges are built into the imaging system. The principal component of the system is a piezo-electrically controlled Fabry—Perot interferometer spectrometer. The deparallelisation of the Fabry—Perot mirrors during the scanning, caused by the “fatigue” of the piezo-electrical system, was eliminated using suitable circuits. The good performance of the interferometer was checked by measuring of the finesse and resolution of selected spectral lines of different spectral lamps and the resonance radiation of a He---Ne gas laser. The optical set-up is suitable for general spectroscopic and spectrographic observations, for measuring radial intensity distributions, for obtaining high resolution spectra and for the determination of intensity ratios in the radiation of the twin hollow cathode source in the visible spectral range.