The Reaction of Singlet Oxygen with 1,3-Dimethylindole in the Presence of Aldehydes. Formation of 1,2,4-Trioxanes

The dye-sensitized photo-oxygenation of 1,3-dimethylindole in the presence of aldehydes initially generates a zwitterionic peroxide which condenses with the carbonyl function to give the corresponding cis-fused 1,2,4-trioxanes. Acetaldehyde gives a pair of diastereomers, one of whose structures was determined by X-ray analysis (cis,cisisomer), whereas pivaladehyde gives only the cis,cis diastereomer.     

A stable 3-methylene-1,4-cyclohexadiene: a non-aromatic tautomer of a simple benzene

2,4-Dichloro-3-(dimethylaminomethylene)-1,4-cyclohexadiene-1,5-dicarboxaldehyde, a stable derivative of the reactive $\text{p}$-isotoluene, has been isolated by treating cyclohexane-1,3-dione with a Vilsmeier reagent.     

The intramolecular mode in isotopically substituted NO+ β- and β″-alumina

Single crystals of ¹⁵N-substituted NO⁺ β- and β″-alumina were prepared and Raman scattering spectra of the nitrosonium intramolecular stretching mode were measured. The harmonic frequency and the cubic anharmonic force constant were calculated using these and similar data from the naturally abundant nitrosonium aluminas. Differences in the calculated values between the β and β″ system were attributed to structural differences in the conduction planes.     

A linear system solver based on a modified Krylov subspace method for breakdown recovery

Despite its usefulness in solving eigenvalue problems and linear systems of equations, the nonsymmetric Lanczos method is known to suffer from a potential breakdown problem. Previous and recent approaches for handling the Lanczos exact and near-breakdowns include, for example, the look-ahead schemes by Parlett-Taylor-Liu [23], Freund-Gutknecht-Nachtigal [9], and Brezinski-Redivo Zaglia-Sadok [4]; the combined look-ahead and restart scheme by Joubert [18]; and the low-rank modified Lanczos scheme by Huckle [17]. In this paper, we present yet another scheme based on a modified Krylov subspace approach for the solution of nonsymmetric linear systems. When a breakdown occurs, our approach seeks a modified dual Krylov subspace, which is the sum of the original subspace and a new Krylov subspaceK _m (w _j ,A ^T ) wherew _j is a newstart vector (this approach has been studied by Ye [26] for eigenvalue computations). Based on this strategy, we have developed a practical algorithm for linear systems called the MLAN/QM algorithm, which also incorporates the residual quasi-minimization as proposed in [12]. We present a few convergence bounds for the method as well as numerical results to show its effectiveness.Research supported by Natural Sciences and Engineering Research Council of Canada.     

The synthesis of 4-methyl-2-pyrrolidones and 3-methyl-1-pyrrolidines and their mass spectral study

A number of 1-alkyl-4-methyl-2-pyrrolidones have been prepared from methyl 4-alkylamino-3-methyl butenoates. The corresponding 1-alkyl-3-methyl-pyrrolidines are obtainable by the reduction of the pyrrolidones with lithium aluminum hydride. The mass spectra of pyrrolidones and pyrrolidines have been studied. Three different mechanisms which lead to the base peak have been proposed.     

Thermolysis of the phenyltin chlorides,PhxSnCl4–x, (x=1−3): Products and pathways

The thermal degradation of triphenyltin chloride, diphenyltin dichloride and phenyltin trichloride has been studied by pyrolysis at 375°C in sealed tubes for various time periods. In all cases, biphenyl and tin(II) chloride are produced. For both phenyltin trichloride and diphenyltin dichloride, ter- and poly-phenyls are also obtained. In some cases tin(IV) chloride or elemental tin are obtained. Pathways that account for all observed products are presented.     

Chemical origin of thermally stimulated discharge currents in polyacrylonitrile

Thermally stimulated discharge has been used in the past to diagnose and estimate the magnitude of electrical polarization in polymers. Nevertheless, molecular characterization of operative phenomena by this technique alone is often a difficult task. In the present work, infrared attenuated total reflection spectroscopy has been used to investigate the origin of thermally stimulated discharge currents near 200°C in externally unpolarized films of polyacrylonitrile (PAN). Spectroscopic analysis of thermally degraded films reveals some unsaturation of the PAN backbone and possibly the generation of cyanide ions. Opposite surfaces in a solvent-cast film give different spectra, indicating a gradient in chemical degradation products across the film thickness. Data suggest that nonuniform generation of charged species and unsaturated bonds gives rise to internal potentials in PAN. The origin of thermally stimulated currents in PAN near 200°C is thus believed to be associated with the onset of chemical degradation.