Disclosing Cyclic(Alkyl)(Amino)Carbenes as One-Electron Reductants: Synthesis of Acyclic(Amino)(Aryl)Carbene-Based Kekulé Diradicaloids

Herein, we disclose cyclic(alkyl)(amino)carbenes (CAACs) to be one-electron reductants under the formation of a transient radical cation as indicated by EPR spectroscopy. The disclosed CAAC reducing reactivity was used to synthesize acyclic(amino)(aryl)carbene-based Thiele and Chichibabin hydrocarbons, a new class of Kekulé diradicaloids. The results demonstrate CAACs to be potent organic reductants. Notably, the acyclic(amino)(aryl)carbene-based Chichibabin's hydrocarbon shows an appreciable population of the triplet state at room temperature, as evidenced by both variable-temperature NMR and EPR spectroscopy.     

Vibrations of initially stressed cylinders of variable thickness

Natural frequencies and buckling loads for cylindrical shells having linearly varying thickness are obtained by using a segmentation technique. The present results for free vibration of a cylinder compare very well with those obtained previously. The effect of the thickness variation on the frequencies of a cylindrical shell is studied. Frequencies are also calculated for a cylinder of variable thickness under axial compression and a relationship between the frequency and axial compression is obtained for a particular wave number.     

Kinetics and mechanism of the oxidation of some neutralized α-Hydroxy acids by hexachloroiridate(IV)

Summary The kinetics of oxidation of some neutralized -hydroxy acids such as lactic (LA), mandelic (MA), -hydroxyisobutyric (IB) and benzilic (BA) acid by hexachloroiridate(IV) have been studied. The oxidation products are acetaldehyde, benzaldehyde, acetone and benzophenone for the respective reactions, which are first order with respect to each substrate and to iridium(IV). The reaction rate increases with increase in pH and salt concentrations. The temperature influence is quite marked in all these reactions. A mechanism involving the formation of an unstable complex, which decomposesvia a free radical pathway to give the respective reaction products, is proposed.     

Structure property correlation in crosslinkable copolyimides

Three copolyimides containing crosslinkable alkyne groups either in the main chain backbone or as endgroups, have been synthesized and characterized in regard to their structure, molecular weight, solubility, film-forming properties, crystallinity, crosslinking behavior, and thermal stability. A good correlation between the structure of the polymers and their properties has been established.     

Phosphorus containing polymers. III. Polyimidophosphonates

Synthesis of dihydroxybisimide monomers and their subsequent polycondensation with dichlorophenylphosphine oxide by use of a phase-transfer catalyst are reported. The monomers were characterized by melting point, elemental analysis, and IR spectroscopy. The polyimidophosphonates were characterized by viscosity measurement, molecular weight determination, elemental analysis, IR, ESCA, ¹H-NMR, ³¹P-NMR, and X-ray diffraction. Thermal stability and glass transition temperature (T_g) of the polymers were evaluated by TGA, DTA, and TMA. These polymers are self-extinguishing and readily soluble in highly polar solvents like DMF, DMSO, DMAC, NMP, HMPA, etc. © 1994 John Wiley & Sons, Inc.     

Quantum analogue of the Kolmogorov–Arnold–Moser transition in different quantum anharmonic oscillators

The results of numerical computations are presented for the Bohmian trajectories of the family of different one‐ and two‐dimensional anharmonic oscillators, which exhibit regular or chaotic motion in both classical and quantum domains, depending on the values of the parameters appearing in the respective Hamiltonians. Quantum signatures of the Kolmogorov–Arnold–Moser (KAM) transition from the regular to chaotic classical dynamics of these oscillators are studied using a quantum theory of motion (QTM) as developed by de Broglie and Bohm. A phase space distance function between two initially close Bohmian trajectories, the associated Kolmogorov–Sinai–Lyapunov (KSL) entropy, the phase space volume, the autocorrelation function, the associated power spectrum, and the nearest‐neighbor spacing distribution, clearly differentiate the quantum analogues of the corresponding regular and chaotic motions in the classical domain. These quantum anharmonic oscillators are known to be useful in several diverse branches of science. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Convenient Preparation of Optically Pure 3‐Aryloxy‐pyrrolidines

Chiral 3‐methanesulfonyl‐1‐Boc‐pyrrolidine and piperidine were reacted with sodium phenolates, resulting in a mixture of displacement and elimination products. Following carbamate deprotection and pH adjustment, the 3‐pyrroline and tetrahydropyridine by‐products resulting from elimination were easily removed through aqueous partitioning and/or concentration. Although the pyrrolidines were formed with a high degree of optical purity, slight racemization was observed for the piperidine case because elevated temperatures were required to effect displacement.