Search results for "condensation"

1989

Polymides 3a and 3b with stiff-chains bearing trioxaoctyl or tetraoxaundecyl side chains were synthesized and characterized. The polycondensation was done with pyromellitic anhydride and N,N′-bis(1-imidazolylcarbonyl)-2,5-(1,4,7-trioxaoctyl)- or 2,5-(1,4,7,10-tetraoxaundecyl)-1,4-phenylenediamine (2a or 2b). 3b, being sufficiently soluble, was characterized by 13C NMR spectroscopy. The results of IR and 13C NMR spectroscopy prove the presence of the correct imide structure. In solid state 3a and 3b form layered structures with the side chains being in a disordered state.

Bis-, Tris-, and Tetrakis(squaraines) Linked by Stilbenoid Scaffolds

2001

The oligosquaraines 1−5, with stilbenoid scaffolds, were prepared by multistep syntheses in which the final steps consisted of condensation reactions between the semisquaric acid 21 and multiple resorcinols 12b−15b and 17b. The target compounds exhibit intense (ϵ > 250000 L·mol−1·cm−1) and sharp absorption bands with maxima between 687 to 778 nm, depending on the conjugation in the stilbenoid scaffold. Comparison with the monosquaraine 6 as a model compound reveals intramolecular interactions between different donor−acceptor−donor moieties, which give rise to increased absorption intensities.

ChemInform Abstract: Bis-, Tris-, and Tetrakis(squaraines) Linked by Stilbenoid Scaffolds.

2010

The oligosquaraines 1−5, with stilbenoid scaffolds, were prepared by multistep syntheses in which the final steps consisted of condensation reactions between the semisquaric acid 21 and multiple resorcinols 12b−15b and 17b. The target compounds exhibit intense (ϵ > 250000 L·mol−1·cm−1) and sharp absorption bands with maxima between 687 to 778 nm, depending on the conjugation in the stilbenoid scaffold. Comparison with the monosquaraine 6 as a model compound reveals intramolecular interactions between different donor−acceptor−donor moieties, which give rise to increased absorption intensities.

Dodecyloxy-substituted 2,4,6-tris(styryl)pyridines

2008

(E,E,E)-2,4,6-Tris(styryl)pyridines 2a-c with 3, 6 or 9 dodecyloxy substituents were prepared by the highly stereoselective condensation reaction of collidine (8) and the corresponding phenyl-(1-phenyl-methylidene)amines 7a-c (Siegrist reaction). In contrast to the corresponding compounds with a benzene or a 1,3,5-triazine core, 2a-c do not show any hints for the formation of thermotropic liquid crystals. The major application of such star-shaped systems is in the field of nonlinear optics.

Size Matters More Than Chemistry for Cloud-Nucleating Ability of Aerosol Particles

2006

Size-resolved cloud condensation nuclei (CCN) spectra measured for various aerosol types at a non-urban site in Germany showed that CCN concentrations are mainly determined by the aerosol number size distribution. Distinct variations of CCN activation with particle chemical composition were observed but played a secondary role. When the temporal variation of chemical effects on CCN activation is neglected, variation in the size distribution alone explains 84 to 96% of the variation in CCN concentrations. Understanding that particles' ability to act as CCN is largely controlled by aerosol size rather than composition greatly facilitates the treatment of aerosol effects on cloud physics in re…

New Fluorinated 1,3-Vinylogous Amidines as Versatile Intermediates: Synthesis of Fluorinated Pyrimidin-2(1H)-ones.

2006

The condensation of the azaenolates derived from readily available ketimines with fluorinated nitriles offers an efficient and straightforward entry to new fluorinated 1,3-vinylogous amidines. These versatile compounds, in turn, react with triphosgene to yield new fluorinated pyrimidin-2(1H)-ones in high yields.

In situ ATR-IR studies in aqueous phase reforming of hydroxyacetone on Pt/ZrO2 and Pt/AlO(OH) catalysts: The role of aldol condensation

2018

Abstract In situ Attenuated Total Reflection Infrared (ATR-IR) spectroscopy was used to study Aqueous Phase Reforming of hydroxyacetone on Pt/AlO(OH) and Pt/ZrO2 catalysts at 230 °C/ 30 bar. Formation of strongly adsorbed aldol condensation products was observed on the surface of Pt/ZrO2 and ZrO2 in contrast to Pt/AlO(OH) and AlO(OH). Peak assignments were supported by DFT calculations of the IR spectra of the condensation products in vacuum and in the presence of water. Aldol condensation of hydroxyacetone leading to compounds with high molecular weight with unsaturated bonds was suggested as a first step in coke formation. Carbonaceous deposits on the surface of the ZrO2 support are oxyge…

Fracture resistance of roots filled with three different obturation techniques

2012

Objectives: The aim of this study was to compare in vitro root fracture resistance following root canal filling with AH 26 using lateral condensation, BeeFill, and Thermafil techniques. Study Design: Eighty extracted human mandibular premolars with similar dimensions were selected. In order to standardize the roots, measurements were taken in two separate regions of the teeth—at the cemento-enamel junction and 8 mm apically from the junction—buccolingual as well as mesiodistal for every tooth. Teeth were then randomly divided into five groups (n=16). With the exception of the non-prepared group (Group 1), instrumentation was done in all groups. In group 2, instrumentation but no filling was…

Applications of light-matter interaction in nanosciences

2009

In this thesis, light matter interaction in nanoscale has been studied from various aspects. The interaction between surface plasmon polaritons (SPPs) and optically active organic molecules (Rhodamine 6G, Sulforhodamine 101 and Coumarine 30) and semiconducting nanocrystals (quantum dots) is studied in the weak coupling regime. In particular, a photon-SPP-photon conversion with spatially separated inand outcoupling was demonstrated by using molecules. Also, a frequency downconversion for propagating SPPs was presented by utilization of vibrational relaxation of organic molecules. A strong coupling regime was reached for Rhodamine 6G (R6G) and SPP despite the broad absorption linewidth of R6G…

Macrocyclic hexaureas: synthesis, conformation, and anion binding.

2009

Varied flexibility: Cyclic oligoureas are formed by using anions as templates. Linking of six xanthene and/or diphenyl ether fragments by urea groups leads to the formation of five macrocyclic compounds with a 48-membered ring with variable flexibility (see picture). Their interaction with anions shows a strong influence of acetate and chloride ions on the cyclization from four precursor molecules. Five macrocylic compounds XXXXXX, XXDXXD, XDXDXD, XDDXDD, and DDDDDD with 48-membered rings, in which six xanthene and/or diphenyl ether fragments are linked through six urea (-NH-C(O)-NH-) groups, have been synthesized. In the cyclization step, a linear diamine was allowed to react with the appr…