Cyloadditions of benzopyrones: Rapid access to bicyclic AB-ring analogues of anthracyclines

Cycloaddition of the benzopyrone 10b with 1,1-disubstituted alkenes 12, 14, and 16 produces fair yields of the lactones 13, 15, and 17, AB-ring analogues of the anthracyclines.     

Effect of temperature and molecular weight on the rate of spreading of polystyrene melts on plane soda lime glass surfaces

The effect of temperature T and weight-average molecular weight M?_w on the rate of spreading of polystyrene melts on plane solid surfaces has been examined. The activation energy E of spreading was estimated to be 25.2 ± 3 kcal/mole, which is of the same magnitude as the activation energy for flow of polystyrene melts. The rate of spreading was found to be inversely proportional to M?_w raised to the 1.5 power. This rate of spreading, measured as the time rate of increase in the liquid–solid contact area, dA/dt, could be expressed as where γ_1v is the melt surface tension and θ_d and θ_s are the dynamic and static contact angles, respectively. The numerical value of K has been calculated to be (6.025 ± 3.693) × 10^?14 in the temperature range of 110–260°C and for the values of M?_w from 2000 to 37000.     

Self-Sensitized Photo-Oxygenation of 1-Benzyl-3, 4-dihydroisoquinolines

The air oxidation of 1-benzyl-3, 4-dihydroisoquinolines is shown to be a self-sensitized photo-oxidation proceeding via singlet oxygen.     

An unusual stereospecific epoxidation with “per-amberlyst 15®”

4-Methyl-4-naphthoquinol and its 5-methyl derivative on treatment with per-Amberlyst 15 are converted to the corresponding cis-2,3-epoxides in high yields. The latter structure was determined by X-ray crystallography.     

Light scattering from nonequilibrium electron-hole plasma excited by picosecond laser pulses in GaAs

A picosecond dye laser is used to excite electron-hole plasma of density between 10¹⁸ to 10¹⁹ cm^-3 in GaAs. The plasma density and distribution function within ? 20 psec of excitation is probed by Raman scattering. The lineshape of the single particle excitation spectra of the plasma can be explained only by assuming that the electron distribution function is in nonthermal equilibrium.     

Molecular dynamics by the Backward-Euler method

This paper introduces a new computational method for molecular dynamics. The method combines the Backward-Euler scheme for the solution of stiff differential equations with a Langevin-equation approach to the establishment of thermal equilibrium. The method allows the user to choose a cutoff frequency ω_c. Vibrational modes with frequencies below ω_c will be fully excited (receive a mean energy of kT per mode), while modes with frequencies greater than ω_c will be effectively frozen by the method. By setting ω_c = kT/h, one can obtain reasonable agreement with the quantum-mechanical energy distribution among the various modes, despite the classical character of the computation.     

Slowly oscillating functions and a generalization of quasi-monotone coefficients

We first state a conjecture due to Yong concerning equality of two classes of functions, and then give examples to disprove the conjecture. Later we extend some theorems concerning integrability of Fourier series.