MO-LCAO-Berechnungen an Polymethinen. XI Lokale spektrale Anregungen in polynuclearen Cyaninfarbstoffen

MO-LCAO Calculations on Polymethines. XI. Local Spectral Excitations in Polynuclear Cyanine Dyes Various branched-conjugated cyanine dyes display long-wavelength absorption bands similar in position to those of their straight-chain substructures. According to the analysis of results of PPP-type calculations this close similarity results from a partial localization of the electronic transitions, whereas the participating electronic states are highly delocalized. The long-wavelength absorptions of symmetrically-branched trinuclear cyanine dyes have an entire molecular chromophore origin resulting from twofold degenerate electronic transitions. Lowering of the symmetry brings about a splitting of the colour-band. In contrast to the branched-conjugated cyanine dyes various tetranuclear cyanine dyes can be considered as being composed of two subchromophores either directly linked or joined through a conjugative bridge. In accordance with PPP configuration analyses and LHM-type calculations the splitting of the colour band is best understood by composite-molecule approaches. In this context the applicability of the simple molecular exciton theory is discussed.     

MO-LCAO-Berechnungen an Polymethinen. IX. Zur Farbigkeit gekoppelter Oxonol- und Cyaninfarbstoffe

MO-LCAO Calculations on Polymethines. IX. On the Chromaticity of Coupled Oxonol and Cyanine Dyes Streptopolymethines display low-energy electronic transitions with a high transition probability and possess, moreover, a high capability to accept or to release electrons. These properties account for the absorption colour of polymethine dyes consisting of two molecular fragments. Scope and limitations of a composite-molecule approach can be recognized by subjecting the electronic wavefunctions to the so-called configuration analysis. Colour-structure relationships are derived from inspection of key orbital interactions between the molecular fragments.     

Zum Stand der Schwefelsäure-Produktion

Sulphuric acid production – state of the art. Apart from pyrites and other metal sulfides, sulphur is mainly used today as raw material for the production of sulphuric acid. The oxidation of roaster gases or sulphur combustion gases is performed almost exclusively in multistage reactors over catalysts containing vanadium pentoxide. SO₂ conversions of more than 99.5% are achieved by intermediate absorption of SO₃ (“double catalysis”) and by using efficient catalysts. To further improve the economics of the manufacturing process, new technologies are being tried out, and attempts are being made to develop even more active catalysts. Although there is still some uncertainty regarding the kinetics of SO₂ oxidation, empirical findings can be explained quite satisfactorily with existing models.     

Derivate des Phosphorsäure-o-phenylenesters. XIX. Zum Ablauf der Bromierung von Phenyl-o-phenylenphosphit

Derivatives of o-Phenylene Phosphates. XIX. Bromination of Phenyl o-Phenylene Phosphite The bromination of phenyl o-phenylene phosphite does not yield the expected penta-coordinated phosphorus dibromide 3 but phosphorus tribromide, phenoxy-bis-(o-phenylendioxy)-phosphorane and tetraphenoxyphosphonium bromide. The mechanism of the reaction is discussed.     

Struktur und Eigenschaften von ABS-Polymeren. IV. Zum Einfluß der thermischen Vorbehandlung auf das Deformationsverhalten von ABS-Pfropfpolymerisaten

The influence of thermal history on the thermomechanical properties of a graft polymer (ABS) is investigated. The thermal pretreatments are: sharp quenching from above the glas-transition of the matrix resin, annealing below the glas transition. A first characterization of the influence of these two pretreatments is done by measuring density, probe length as function of temperature and by DTA. The less modulus in the region below the glas transition of the matrix resin is very sensitive to thermal pretreatment. Small but reproducible influences are observed in the glas transition region of the polybutadien particles. At room temperature stress-strain measurements are achieved until fracture happens. Crazing is observed (which is often called stress-whitening) in all cases, but the extent of craze growing is dependent on thermal history. The measurements are completed by scanning micrographs of the fracture surfaces. Annealing of the fracture surfaces gives additional informations. The results are discussed using the concept of free volume which is variated by thermal pretreatment. At room temperature the phase-boundary between polybutadion particle and matrix resin is considered as transition zone from high to small hole concentration. The sharpness of this zone is supposed to be a decisive parameter for the macroscopic deformation behaviour.     

Zum mechanismus der eletrochemischen ameisensäureoxidation in saurem leitelektrolyten

Current/voltage plots with formic acid in acid electrolytes at noble metal electrodes show in general three anodic peaks. In the potential range of the first peak the acidic H-atom is split off and oxidized. At constant potential the current decreases with time due to poisoning of the electrode by intermediate products. At the second and third peaks non-specific electrochemical or chemical reactions (coverage of the electrode by chemisorbed oxygen) are followed by a pure chemical oxidation of formic acid.

Résumé

Les courbes (tension, courant) d'électrolytes acides + acide formique avec électrodes de métaux nobles, manifestent généralement trois pics anodiques. L'intervalle de tension correspondant au premier traduit l'oxydation de l'atome N acide. A tension constante, le courant décroit en fonction du temps, ce qui est dû á l'empoisonnement de l'électrode par des produits intermédiaires. Au 2e et au 3e pic, des réactions non spécifiques, électrochimiques ou chimiques (telles que recouvrement de l'électrode par oxygéne chimi-sorbé) sont suivies par l'oxydation purement chimique de l'acide formique.     

Polyreaktionen an pigmentoberflächen. IV. Mitteilung: Polymerisation von n-carboxy-α-aminosäureanhydriden auf der oberfläche von siliciumdioxid

Silica with covalent bound amino-phenyl groups on its surface is used as initiating agent for the polymerization of N-carboxy-α-amino-acid anhydrides (NCAs). The polymerization rate of the amino-phenyl silica initiated polymerization is about three times faster than the polymerization rate of the polymerization initiated by the comparable low molecular compound p-toluidine (propagation rate constant for the polymerization of L-leucine NCA initiated by amino-phenyl silica in dioxane at 15°C: k = 1,8 · 10^?2 1 · mol^?1 · sec^?1). Both reactions show similar conversion-time curves, which are determined by the slow initiation step. By the reaction of amino-phenyl silica with NCAs, silica polypeptides are obtained with an unextractable polymer content from 20 to 85%, while by adsorption only a little amount of polypeptide (about 5%) is irreversibly bound to the silica surface. With a good solvent, the graft polymer is separable into a soluble and an insoluble silica-polypeptide, but not into silica and polypeptide. These facts and the reaction mechanism indicate a covalent bond between silica and polypeptide.