Restricted rotation about the BN bond in aminoboranes: the determination of activation parameters using 13C NMR

In suitable cases, VT ¹³C NMR can provide a rapid and reliable method for obtaining activation parameters ΔH^★ and ΔS^★ for restricted rotation about the B  N bond in aminoboranes.     

Brillouin and ultrasonic study of the temperature dependence of the elastic constants in NaCN

The temperature dependence of the elastic constants of NaCN has been studied by propagation of ultrasonic waves at 15 MHz and by Brillouin scattering at 3 GHz over the temperature range from 287K to 355K. c₄₄ is observed to soften linearly with temperature as the order-disorder phase transition at 284K is approached from above. The other elastic constants also soften, except for c₁₂ which stiffens. Considerable dispersion is seen in the values of c₄₄ obtained ultrasonically and by Brillouin scattering. Measurements of the temperature dependence of the density are also reported.     

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.