Phosphoranes par fermeture trans-annulaire: III—Conformation—configuration—labilité

The analysis of the n.m.r. spectra of the two isomers of 1,6,6-trimethyl-3-phenyl-2,8-dioxa-5-aza-1-phospha ^vbicyclo[3.3.0]octane allows us to propose a conformation for each 5-membered ring and for the configuration of the phosphorus atom. The lability of the H? P proton, revealed by high temperature experiments and by P? H ? P? D exchange, is significantly different in the two isomers.     

Triplet—triplet annihilation and exciton—exciton interactions

A theoretical discussion is presented on the nature of direct and indirect interactions between two triplet excitons. It is shown that the direct exciton interaction through the coulombic interaction of electrons is important when there is a large change in the polarizability of the molecule during its excitation. The indirect exciton—exciton interaction is mainly due to the exciton—phonon interaction arising from the variation in the D-shift term. It is independent of temperature and spin substate. It is attractive in nature for excitons of narrow band-width, and if the exciton—acoustic phonon coupling is inducing the indirect interaction, it falls as R⁻³. It is suggested that a kinematic theory of the triplet—triplet annihilation should incorporate the effects of such interactions.     

Partial phase diagrams for the water—cadmium nitrate, water—silver nitrate and water—cadmium nitrate—silver nitrate systems

Sub-ambient differential scanning calorimetry has been used to determine partial binary phase diagrams for the water—silver nitrate and water—cadmium nitrate systems. Both systems are shown to be eutectic with eutectic temperatures of 263 ± 0.5 K and 256.5 ± 0.5 K for the water—silver nitrate and water—cadmium nitrate systems, respectively. The eutectic compositions are at approximately 40.5 wt.% nitrate for each system. The freezing of ternary solutions containing a fixed silver nitrate/cadmium nitrate ratio but increasing concentrations of total nitrates are explained in terms of a partial ternary system containing two binary eutectic systems and a ternary eutectic reaction. The ternary eutectic temperature is shown to be 254 ± 0.5 K.     

Relativity and the chemistry of UF6: A molecular Dirac—Hartree—Fock—CI study

The electronic structure and bonding of UF₆ and UF₆⁻ are studied within a relativistic framework using the MOLFDIR program package. A stronger bonding but more ionic molecule is found if one compares the relativistic with the nonrelativistic results. The first peak in the photoelectron spectrum of Karlsson et al. is assigned to the 12γ_8u component of the 4t_1u orbital, in agreement with other theoretical and experimental results. Good agreement is found between the experimental and theoretical 5f spectrum UF₆⁻. Some properties, like the dissociation energy and electron affinity, are calculated and the necessity of a fully relativistic framework is shown. The Breit interaction has an effect on the core spinors and the spin-orbit splitting of these spinors but the influence on the valence spectrum is negligible. © 1996 John Wiley & Sons, Inc.     

QCLDB—Quantum chemistry literature data base—a trial

A brief account of a quantum chemistry literature data base (QCLDB ) is described, which contains the key information of about 2000 papers of ab initio calculations of atoms and molecules published in 1977–1979. The QCLDB is stored in a computer and can be sorted and rearranged into author and substance indices. Selection of the items for each paper in a computer-readable data base is discussed.     

The structural rule of Mo—Fe—S cluster compounds

By means of the structural rule, 9N-L, of transition metal cluster compounds, a relationship between the spin property and the structure of Mo-Fe-S clusters is proposed. The relationship can be further revealed by performing EHMO quantum chemical calculations. Also the theoretical maximum values of spin are in accordance with experimental results.     

Pentazol‐Derivate und daraus entstehende Azide: [O3S—p‐C6H4—N5]— und [O3S—p‐C6H4—N3]— als Kalium‐Kronenether‐Salze

Pentazole Derivates and Azides Formed from them: Potassium‐Crown‐Ether Salts of [O₃S—p‐C₆H₄—N₅]^— and [O₃S—p‐C₆H₄—N₃]^{— —}O₃S—p‐C₆H₄—N₂⁺ was reacted with sodium azide at —50 °C in methanol, yielding a mixture of 4‐pentazolylbenzenesulfonate and 4‐azidobenzenesulfonate (amount‐of‐substance ratio 27:73 according to NMR). By addition of KOH in methanol at —50 °C a mixture of the potassium salts K[O₃S—p‐C₆H₄—N₅] and K[O₃S—p‐C₆H₄—N₃] was precipitated (ratio 60:40). A solution of this mixture along with 18‐crown‐6 in tetrahydrofurane yielded the crystalline pentazole derivate [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₅]·THF by addition of petrol ether at —70 °C. From the same solution upon evaporation and redissolution in THF/petrol ether the crystalline azide [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·THF was obtained. A solution of the latter in chloroform/toluene under air yielded [K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·1/3H₂O. According to their X‐ray crystal structure determinations [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₅]·THF and [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·THF have the same kind of crystal packing. Differences worth mentioning exist only for the atomic positions of the pentazole ring as compared to the azido group and for one THF molecule which is coordinated to the potassium ion; different orientations of the THF molecule take account for the different space requirements of the N₅ and the N₃ group. In [K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·1/3H₂O there exists one unit consisting of one [K‐18‐crown‐6]⁺ and one [O₃S‐C₆H₄—N₃]^— ion and another unit consisting of two [O₃S‐C₆H₄—N₃]^— ions joined via two [K‐18‐crown‐6]⁺ ions and one water molecule. The rate constants for the decomposition [O₃S‐C₆H₄—N₅]^— → [O₃S‐C₆H₄—N₃]^— + N₂ in methanol were determined at 0 °C and —20 °C.     

ChemInform Abstract: On Squaring Triangles — Structural Motifs in Cu—In—Sb Compounds.

Two new compounds, Cu₇In_2.5Sb_0.5 (I) and Cu₂In_0.75Sb_0.25 (II) are prepared from the elements (silica ampules, 1173 K, 3 d, followed by annealing at 573—773 K for 220 d).     

Highly reactive metals from potassium—graphite. Preparation and use of titanium—graphite and tin—graphite

The potassium—graphite route to active forms of metals has been extended to the preparation of titanium—graphite (Ti---Gr) and tin—graphite (Sn---Gr). The Ti---Gr is used to achieve the reductive coupling of ketones to give alkenes, and Sn---Gr is used in the preparation of diallyltin dibromide complexes which react with aldehydes to give homoallylic alcohols.     

The reaction of triphenylmethylhalophosphines with tetrachloro‐orthobenzoquinone: Oxidation—isomerization—dehydrohalogenation

Treatment of solutions of the halophosphines TrtP(H)F (Trt = trityl, Ph₃C) 1a and TrtP(H)Cl 1b with equimolar amounts of TOB (tetrachloro‐orthobenzoquinone) led to the formation of mixtures of products. They contained the phosphoranes 2a and 2b, which were formed by oxidation with TOB and are in equilibrium with the phosphines 3a and 3b. Moreover, the trityl phosphonite 4, which was formed by dehydrohalogenation of 2a, 2b and 3a, 3b, was observed in both mixtures. The dehydrohalogenation was found to be reversible in the case of HF. The pure compounds 4 and 5 were obtained from the reaction of TrtPCl₂ with tetrachlorocatechol 4 and by the oxidation of 1a and 1b with two equivalents of TOB. Because of its importance in this reaction sequence, an X‐ray crystal structure determination was carried out on 4. The P–O bond lengths of 168.4(2) and 167.7(2) pm are probably to be attributed to a bond‐lengthening effect of the chlorine atoms of the quinone. As a comparison with analogous systems reveals, the phosphorane 5 is an example of a σ⁵λ⁵(P) species in which the phosphorus atom exhibits square‐pyramidal coordination. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 277–280, 1999     

Stability of electrons—monomers and dimers—in gamma-irradiated hydroxide glasses

The increase of temperature from 77 K brings about the retrapping of electrons and/or recombination processes manifested by the changes of absorption spectra and ESR signals. The new absorption bands at 700–840 nm, which belong to diamagnetic electron dimers, have been observed at 215–225 K. These species are connected with NaOH·X H₂O hydrates as it has been shown by near-IR spectra. The dispersive kinetic parameters of photobleaching of electrons—monomers and dimers—at 80 K have been measured.     

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.     

Untersuchung der binären Systeme von Alkoxy-silan—Alkohol und Phenoxy-silan—Phenol

On ground of DK and IR investigations it can be ascertained that the alkyl-alcoxy-silane—alcohol mixtures shows complex forming mainly at 2:1 molar ratio composition. In the case of monofunctional silane-alcohol mixtures this could be proved only on ground of infrared spectra. From the shifting on the v OH vibration the strength of the hydrogen bridge bond was calculated to be 4.29 kcal/mole. The ability to form complexes with acceptor character increases in direction of the tetra-function, and the disposition to form complexes with donor character in direction of the mono-function. In the associates the silicium atom is in sp³d hybridisation state. On ground of the DK and IR investigations on the mixtures of alkyl-phenoxy-silane—phenol it can be ascertained, that the complex forming is strongest at 1:1 molar ratio composition.     

Investigations into the formation and characterization of microemulsions. I. Phase diagrams of the ternary system water—sodium alkyl benzene sulfonate—hexanol and the quaternary system water—xylene—sodium alkyl benzene sulfonate—hexanol

The phase diagrams of the ternary system water—sodium alkylbenzene sulfonate (NaDBS)-hexanol and the quaternary system water—xylene—NADBS—hexanol have been established at three different temperatures, namely 25, 37, and 50°C. The different phases formed have been qualitatively examined using optical (phase contrast and polarizing) microscopy. The textures of the various liquid crystalline phases in the ternary system have been identified, by comparison with previous studies in the literature. Some of the liquid crystalline phases have been quantitatively assessed using low angle X-ray diffraction. The latter measurements were also used to determine the unit cell dimensions in the various phases studied. With the quaternary system, particular attention was paid to the transparent region which consisted of an L₂ (inverse micellar) phase extending into another transparent region which has a blue “tinge” in some cases, namely the microemulsion (M) region. The amount of water solubilized in the L₂ (reverse micelle) or M + L₂ phase was calculated from the phase diagrams. With the ternary system the results showed a maximum in moles of water solubilized per mole total surfactant (NaDBS + hexanol) at a concentration of 0.3 mole surfactant, at an optimum molar ratio of n-hexanol to NaDBS of 4.5:1. This maximum was about twice with the quaternary system, when compared with that of the ternary system, indicating the importance of the role of xylene in solubilization of water by the surfactants. The present investigation has also shown that the extent of the microemulsion region is significantly reduced by increases of temperature when the NaDBS is lower than 15 wt%.     

1,2-dihydroisoquinolines—XVIII Rearrangements—IV Dihydroisoquinoline rearrangement—15

When 1-allyl-2-methyl-1,2-dihydropapaverine is treated with hot, dilute mineral acid, rearrangement occurs to give, almost exclusively the 3-allyl-2-methyl-3,4-dihydropapaverinium salt. The previously reported rearrangement of 1-cinnamyl-2-methyl-6,7-dimethoxy-1,2-dihydroisoquinoline has been re-examined and the earlier result, that rearrangement occurs yield the 3-cinnamyl-3,4-dihydroisoquinolinium salt, confirmed.     

Frequency-dependent polarizability of —CC— linked para-nitroaniline monomer through pentamer

Using atomic orbital basis sets calibrated in an earlier study on the monomer and dimer and employing the direct atomic-integral driven strategy of the DISCO program package, we performed self-consistent field level calculations of the frequency-dependent polarizabilities of the monomer through pentamer of —CC— linked para-nitroaniline. These computations, which were performed in parallel using seven IBM RS6000 model 560 workstations, involved up to 612 atomic basis functions and 10¹¹ two-electron integrals, and required solution of linear response equations whose dimensions ranged up to 132000.     

Observation and analysis of rotationally resolved — electronic transitions of CD—Ar

The CD—Ar van der Waals complex has been generated in the gas phase by the 248 nm photolysis of CDBr₃ entrained in a supersonic jet of argon. Rotationally resolved spectra associated with the complex have been observed by laser-induced fluorescence in the vicinity of the CD B ²Σ⁻-X ²Π (1, 0) band near 366 nm. Bands at 27310.7 and 27327.8 cm⁻¹ are rotationally analyzed using computer simulations, and assigned as (1, 0⁰, 0) and (1, 1^p, 0), respectively. The vibronic structure of the CD—Ar excited states has also been analyzed using a model based on hindered internal rotation. The results are compared to those reported for CH—Ar.