Preparation et caracterisation de complexes [cis-4,4′-dinitrodibenzo-18-couronne-6, LnCl3, 3CH3CN]

Some new complexes between thecis-4,4′-dinitrodibenzo-18-crown-6 and rare earth chlorides LnCl₃ (Ln=Nd, Gd, Yb) were synthesized in acetonitrile. Ligandcis-4,4′-dinitrodibenzo-18-crown-6 and its complexes were identified by infrared spectroscopy, X-ray diffraction and thermal analysis (TG and DTA). Acis-trans isomerisation of the complexed ligand is observed about 148°C when heating the rare earth complex.

     

Die Verwendung von Klathraten der Komplexsalze vom Typ Ni(SCN)2(4-MePy)4 zur Trennung vonCis-Trans-Azobenzolgemischen

Zusammenfassung Zur Trennung voncis- undtrans-Azobenzol wurden Klathrate des Typs Ni(SCN)₂(4-Methylpyridin)₄·0,7(4-Methylpyridin) erfolgreich als Adsorbentien in chromatographischen Säulen verwendet.Die thermische und photochemischecis-trans-Isomerisierung dieser Verbindungen (bei Zimmertemp.) wurden als mögliche Fehlerquellen bei der quantitativen Auswertung der Trennergebnisse untersucht.

---

The application of clathrates formed from complex salts of the Ni(SCN)₂(4-methylpyridine)₄ type to the separation of mixtures of cis- and trans-azobenzenes

The clathrates of Ni(SCN)₂(4-methylpyridine)₄·0,7(4-methylpyridine) type have been successfully applied as sorbents in chromatographic columns to the separation of geometric isomers ofcis- andtrans-azobenzenes.Thermal and photochemicalcis-trans-isomerization of these compounds (at room temperature) have been studied as possible source of errors in the quantitative evaluation of separation results.

---

---

Mit 3 Abbildungen

---

Herrn Prof. Dr.H. Nowotny gewidmet.     

Untersuchungen zur Temperaturabhängigkeit charakteristischer IR-Absorptionen, 5. Mitt.: IR-spektroskopischer Nachweis von fixierten Molekülzuständen bei α-Diketonen

Zusammenfassung IR-spektroskopische Untersuchungen an -Diketonen bei erhöhter Temperatur zeigen, daß zwei räumlich unterschiedliche Anordnungen, denen auf Grund der C=O-Streckschwingungs-absorption quasi-cis-trans-Charakter zukommen muß, bei diesen Substanzen auftreten.

---

An infrared spectroscopic study of the C=O stretching vibration with -diketones at elevated temperatures shows the existence of two different conformations with a quasi-cis-trans-character.

     

Conformational analysis and electronic structure of monothiodiacetamide: Normal coordinate analysis and molecular orbital study

The infrared spectra of monothiodiacetamide (MTDA, CH₃CONHCSCH₃) and its N-deuterated compound in solution, solid state and at low temperature are measured. Normal coordinate analysis for the planar vibrations ofMTDA-d ₀ and –d ₁ have been performed for the two most probablecis-trans-CONHCS-or-CSNHCO-conformers using a simpleUrey-Bradley force function. The conformation ofMTDA derived from the vibrational spectra is supported by the all valence CNDO/2 molecular orbital method. The vibrational assignments and the electronic structure ofMTDA are also given.

---

Konformationsanalyse und elektronische Struktur von Monothiodiacetamid. Normalkoordinatenanalyse und MO-Studie

Zusammenfassung Das Infrarotspektrum von Monothiodiacetamid (MTDA, CH₃CONHCSCH₃) und der entsprechenden N-deuterierten Derivate wurde in Lösung, im Festzustand und bei tiefer Temperatur gemessen. Die Normalkoordinatenanalyse der möglichen planaren Konformeren wurde mittels einer einfachenUrey-Bradley-Funktion durchgeführt. Die dabei abgeleitete Konformation vonMTDA steht im Einklang mit einer semiempirischen quantenchemischen Rechnung (CNDO/2). Die Zuordnung der Schwingungen und die Elektronendichteverteilung inMTDA werden angegeben.

     

Stereochemical effects in the electron impact mass spectra of cis-trans isomeric 1,2,3,4-tetramethylcyclohexanes

The mass spectra of six cis-trans isomeric 1,2,3,4-tetramethylcyclohexanes are discussed. The intensity ratio of [M? CH₃]⁺/[M? C₂H₅]⁺ correlates with the strain energies of the stereoisomers. Therefore, the identification of cis-trans isomers is possible by means of their mass spectra. The mass spectra of deuterium labelled compounds demonstrate favoured fragmentation of the axial methyl groups and ring opening between the cis substituted carbon atoms of the cyclohexane.     

Thermal cis–trans isomerization and decomposition of polyacetylene

Thermal cis-trans isomerization and decomposition of polyacetylene film prepared with a Ti(OC₄H₉)₄–Al(C₂H₅)₃ (Al/Ti = 4) system were investigated under inert gas or in vacuum by means of thermal analysis and infrared spectroscopy. Thermograms of differential thermal analysis of cis-polyacetylene revealed the existence of two exothermic peaks at 145 and 325°C and one endothermic peak at 420°C which were assigned to cis-trans isomerization, hydrogen migration accompanied with crosslinking reaction, and thermal decomposition, respectively. The isomerization was followed by infrared spectroscopy over the temperature range 75–115°C. The reaction did not obey simple kinetics. The apparent activation energy for the cis-trans isomerization was 17.0 kcal/mole for the polymer containing 88% cis configuration and increased with increasing trans content up to 38.8 kcal/mole for 80% trans content.     

Reaction of Aluminium Chloride with Benzo[C]- and Naphtho[2,3-C]pyrans

Aluminium(III) chloride is shown to cause (reversible) cis-trans stereoisomerisations in some benzo[c]- and naphtho[2,3-c]pyrans at ambient temperature.     

Selective Encapsulation and Unusual Stabilization of cis-Isomers by a Spherical Polyaromatic Cavity

To explore new cavity functions, we herein employed cis-trans stereoisomers with a N=N, C=C, or C=N unit as guest indicators for a polyaromatic capsule. Thanks to the rigid, spherical cavity with a diameter of ∼1 nm, azobenzene and stilbene derivatives are quantitatively encapsulated by the capsule with 100 % cis-selectivity in water. The isomerization of the cis-azo compound is suppressed against heat and light in the cavity, due to the confinement effect. Furthermore, C,N-diphenyl imine derivatives are quantitatively encapsulated by the capsule in water and adopt an otherwise unstable cis-form. The polyaromatic cavity suppresses the hydrolysis of the imines in water, even at elevated temperature, due to the shielding effect. Accordingly, the properties of the cis-trans isomers could be largely altered through supramolecular manipulation.     

Model for the direct photo-isomerization of stilbene

The photo-chemical cis-trans isomerization of stilbene is re-interpreted after the introduction of a low-energy doubly excited state.     

Synthesis and Characterization of the First Double-Bridged Tetraselenafulvalenophanes

Recrystallization of the isomeric mixtures of 1 a and 1 b obtained by synthesis gave single crystals of the cis-trans and cis-cis isomers, respectively. The unique stacked structures of these compounds were elucidated by X-ray structure analysis.     

Photoisomerization of AZO Aromatic Chromophobes in Polyvinyl Chloride

Abstract

The synthesis and characterization of new vinyl chloride-p-acryloyloxyazobenzene copolymers are reported. Kinetics of photoinduced trans-cis and thermal cis-trans isomerization of azo pendant groups in copolymer have also been investigated, and the kinetic parameters were evaluated. An azo acrylate model compound was used for comparison.     

Steric Structure of Bis(5,5-dimethyl-3-thioxo-1-cyclohexenyl) Sulfide

Two-dimensional NMR spectroscopy, dipole moment measurements, and quantum-chemical calculations (basis 6-31G^*) were used to show that in the gas phase and in solutions bis(5,5-dimethyl-3-thioxo-1-cyclohexenyl) sulfide prefers a nonplanar cis-trans conformation.     

The mass spectra of small-ring heterocycles. III. Aroylaziridines

The mass spectra of cis-trans isomeric aroylaziridines are presented. Attempts to extend the method for distinguishing between cis and trans isomers previously established for aroylazetidines are described and the results rationalized. A simple fission of the 1-alkylnitrogen bond is described and detailed fragmentation mechanisms are presented and discussed.     

Gas Chromatographic Derivation of the Solubility Parameters of Polychbrinated Biphenyls with the Inclusion of Cis-Trans and Optical Isomerism and Orientational Disorder

Abstract

A thermodynamic model (SOFA) was used to derive molar (subcooled) liquid volume, heat of vaporization and Scatchard-Hildebrand solubility parameters of polychlorinated biphenyls. Differences in molar volume and heat of vaporization between cis-trans isomers and between enantiomers were accounted for by specific fragment contributions and by an increase or decrease of molar volume and heat of vaporization when mixed cis-trans isomers or D-L enantiomers, respectively, occur. The SOFA model was extended by the inclusion of an orientational disorder entropy term. An accurate set of gas chromato-graphic relative retention times (N = 210) and semi-empirical data on heats of vaporization (N = 7) and molar volumes (N = 11) was used for the derivation.

An extremely accurate prediction was obtained. The mean deviations between calculated and experimental values were close to experimental errors. The corresponding correlation coeficients amounted to r = 0.9989, 0.9988, and 0.99996 for heat of vaporization, molar volume and chromatographic retention, respectively. Cis-trans isomerism was predicted in accordance with experimental crystalline data.     

Properties of decalin as a solvent in thermal field-flow fractionation

Summary Cis-trans-decahydronaphthalene (67.85% trans+ 32.15% cis, here briefly referred to ascis-trans-decalin) as a possible solvent for thermal field-flow fractionation is proposed. Different features such as solvent properties with respect to low polarity polymers, availability of basic physicochemical data (viscosity and thermal conductivity in a convenient temperature range), low toxicity and low cost are emphasized. Retention data over a wide range of cold wall temperatures and thermal gradients were collected. Thev correction factor and λ retention data were determined for polystyrene samples over a relative molecular mass range of 11,300–3,950,000 g mol⁻¹. From these data, selectivity values were determined and compared to the commonly found values for polystyrene in different solvent systems. The average value of −0.6 found here forcis-trans-decalin falls in the optimum selectivity solvent-domain.Cis-trans-decalin is thus fully proven as an optimum solvent for ThFFF.     

Separation ofcis andtrans isomers of naturally occurring hydroxycinnamic acids by high-pressure liquid chromatography

Summary The separation of hydroxycinnamic acids has been investigated by high-pressure liquid chromatography using a micro C₁₈ bonded phase. Irradiation oftrans-ferulic and sinapic acids readily gave a mixture ofcis-trans isomers which can be also separated with the system described.     

cis- and trans-N-nitroso-2,4-diphenylazetidines

The synthesis of cis- and trans-2,4-diphenylazetidines as well as that of their N-nitroso derivatives is described. The “abnormal” reduction of the N-nitrosamines gives a cis-trans mixture of the expected 1,2-diphenylcyclopropanes. However, no stereochemical correlations could be made owing to the base-induced isomerization of the starting N-nitrosamines during the course of the reaction.     

Structure of Substituted 5-Chloromethyloxazolidines

By means of ¹H NMR spectroscopy isomerism was demonstrated in N-alkyl substituted 5-chloromethyl-1,3-oxazolidines due to relative cis-trans orientation of substituents in 2 and 5 positions of the ring. The preferred configuration in 2,3-diaryl-5-chloromethyl-1,3-oxazolidines, cis-(2R,5R), was proved by quantum-chemical calculations.     

Enamine formation from anilines and methyl propiolate. The synthesis of 4(1h)-quinolones

The addition of substituted anilines to methyl propiolate produces labile cis-trans mixtures of enamines which can be isomerized by acid, solvent variation, and thermal techniques. Thermal cyclization of these enamines provides a synthesis of 4( lH)-quinolones.     

On the explanation of the biphotonic processes in polyesters containing azobenzene moieties in the side chain

An explanation for the recently observed biphotonic transitions in side-chain polyesters with azobenzene moieties is given on the basis of experimental observations from optical and Fourier-Transform infrared absorption spectra. We present for the first time experimental evidence that a red laser beam at 633 nm causes cis-trans (Z—E) transitions in azobenzene.