Main‐chain syndioregic nonlinear optical polymers. II. Extended pi conjugation and improved thermal properties

Recent results concerning the synthesis of new main‐chain syndioregic nonlinear optical polymers are presented. In particular, the synthesis of polymers with extended pi conjugation in the chromophore and chromophores with improved thermal stability are presented. The nonlinear optical coefficient of several of the polymers and the optical loss at 1.3 and 1.55 μm were measured and are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2824–2839, 2000     

Cross-polarisation to low-gamma nuclei: the first 183W CP/MAS spectra.

The possibility to obtain 183W CP/MAS spectra has been explored. The choice of suitable set-up compounds, convenient set-up procedures and experimental considerations with respect to contact times, TIS and T1 rho interplay, are discussed.     

Aminonitropyridines and their N-oxides

2,6-Diamino-3,5-dinitropyridine 1-oxide has been prepared by mixed acid nitration of 2,6-diaminopyridine, followed by oxidation using hydrogen peroxide in acetic acid. 3,5-Dinitro-2,4,6-triaminopyridine has been prepared by oxidative amination of 2-chloro-3,5-dinitropyridine or 2,6-diamino-3,5-dinitropyridine using potassium permanganate in liquid ammonia, or by “vicarious nucleophilic amination” of 2,6-diarnino-3,5-dinitropyridine using hydroxylamine in aqueous potassium hydroxide. 3,5-Dinitro-2,4,6-triaminopyridine 1-oxide has been prepared by oxidation of 3,5-dinitro-2,4,6-triaminopyridine using hydrogen peroxide in acetic acid, and by “vicarious nucleophilic amination” of 2,6-diamino-3,5-dinitropyridine 1-oxide. Nmr spectroscopy and single crystal X-ray diffraction studies have shown that these compounds have the planar structures and intra- and inter-molecular hydrogen bonding necessary to confer on the materials the high density, the thermal and chemical stability, and the explosive insensitivity required for new insensitive energetic materials.     

(Arene)tricarbonylchromium complexes synthesized on NaX zeolite: solid-state NMR and DRIFTS studies

Various (arene)tricarbonylchromium complexes were synthesized within the confines of NaX zeolite and studied with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and carbon-13 magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy. In each case, the surface complex Cr(CO)3(Oz)3 (Oz represents a framework oxygen of the NaX zeolite) was prepared before a particular arene was added. The arenes benzene, toluene, mesitylene, anisole, and aniline all produce hexahapto pi-complexes physisorbed within the zeolite supercage. DRIFTS spectra show three bands in the carbonyl region indicating less than C3v symmetry. The NMR spectra have narrow carbonyl bands near 240 ppm which indicate rapidly reorienting complexes within the zeolite. The (eta 6-benzene)tricarbonylchromium complex is physisorbed at two sites as indicated both by the DRIFTS spectra and by two carbonyl resonances at 242.5 and 239.1 ppm at 300 K. Variable-temperature MAS NMR shows these two resonances coalescing near 360 K with an activation energy of 48 +/- 6 kJ/mol. When the temperature is decreased to 205 K, the high-frequency carbonyl resonance disappears. The 239 ppm resonance is still narrow at 134 K while MAS sidebands show that the resonance from physisorbed benzene is ca. 200 ppm wide. The complex prepared with pyridine gave a broad resonance as indicated by the spinning sidebands in the MAS NMR spectra. The pyridine complex was identified as Cr(CO)3(C5H5N)3.     

Experimental investigation of energy dissipation in a resonance tube

Zusammenfassung An einem wassergekühlten Resonanzrohr wurde die Leistung gemessen, die in Wärme umgesetzt wird, wenn das Rohr durch Anblasen der Mündung mittels eines Überschallluftstrahls in intensive Schwingungen versetzt wird. Mittels eines Hitzdrahtanemometers wurden auch die Temperaturschwankungen am geschlossenen Rohrende gemessen. Zusätzlich zur bereits beobachteten Grundschwingung wurde eine Oberschwingung höherer Frequenz gefunden, welche innerhalb des Rohres eine qualitativ verschiedene Dissipationsverteilung ergibt. Es wurde festgestellt, dass der gemessene Energieumsatz viel grösser ist, als Berechnungen aus einem einfachen Stosswellenmodell für die Strömung im Rohr ergeben.