Sergey A. Popov

Synthesis of new chiral N-substituted fused pyrazoles and pyrazolinols

Abstract Treatment of β-diketones and the corresponding β-enaminoketones, having modified carane (2-ethyl-6,6-dimethylbicyclo[3.1.0]hexane) and p-menthane (3-ethyl-1-isopropylcyclopentane) skeletons, with aryl- and alkylhydrazines results in regioselective formation of N-substituted pyrazoles or stable pyrazolinols depending on the nature of the substituent at the hydrazine nitrogen.

Droplet spot as a new object in physics of vacuum discharge

It is established experimentally that the burning of a low-current (several and tens of amperes) pulsed (microseconds) vacuum discharge is accompanied by the formation of plasma microbunches around some of the droplets leaving the cathode spot. The parameters of these bunches (electron concentration ne∼1026 m−3 and equilibrium temperature Te∼1 eV) are close to the parameters of cathode-spot plasma. The data obtained suggest that the initial temperature of droplets and the thermionic emission from them play a key role in the formation of such plasma microbunches. By analogy with the well-known cathode and anode spots in vacuum discharges, these droplet plasma formations are classified as “droplet spots.” This work reports the first results on studying the formation dynamics and the characteristics of the droplet spots. It is noted that the concept of droplet spots will require a certain refinement of the plasma formation mechanism in vacuum discharges.

Electrohydrodynamic phenomena on the explosive-emission liquid-metal cathode

The paper describes the results of a direct experimental observation of the development of an electrohydrodynamic instability at an explosive-emission liquid-metal cathode along with a theoretical analysis of the growth and destruction of the protrusion formed on the cathode surface. >

Synthesis of new chiral heterocycles of the pyrazole and 2-isoxazoline types from (+)-3-carene.

Abstract Preparation of chiral heterocyclic compounds of the pyrazole and 2-isoxazoline types starting from natural monoterpene hydrocarbon (+)-3-carene is described. Stereochemical assignment of the compounds synthesized is made by NMR spectroscopy and X-ray analysis together with the data obtained by molecular mechanics and quantum chemical calculations.

Plasma parameters of an arc cathode spot at the low-current vacuum discharge

This paper is devoted to the results of an experimental study of plasma parameters of cathode spot burning on a liquid-metal cathode in vacuum at a low-current (less than 200 A) vacuum arc discharge. Picosecond laser interferometry and absorption shadow imaging were used in a single experiment. Plasma fragments as dense as 10/sup 26/ m/sup -3/ were observed at discharge currents less than 50 A. Such fragments were never observed in arc discharges with currents higher than 100 A or in the breakdown stage of the discharge.

New chiral agents for resolution of racemic cis-permethric and cis-Z-cyhalothric acids

Abstract Resolution of racemic pyrethroid acids (cis-permethric and cis-Z-cyhalothric) using stable optically active amines derived from natural monoterpene (+)-3-carene and prepartion of optically active esters of the pyrethroid acids are described.

Resonant atomic interfero- and shadowgraphy of vacuum arc with gallium cathode

The mechanism of the emission of neutral atoms of the cathode material into the discharge gap of a microsecond low-current vacuum arc with a liquid Ga cathode has been investigated by the method of subnanosecond resonance laser interfero- and shadowgraphy. It has been shown that the cathode material vaporization has a pronounced nonstationary character and occurs both isotropically and in the form of constricted weakly ionized jets with the atom concentration in a jet over 10/sup 17/cm/sup -3/.

SYNTHESIS OF 2-ALKYL AND 2-ARYL PYRIMIDINES FROM β-CHLOROVINYL KETONES OF CYCLOPENTANONE TYPE

Amidines react in the presence of NaHCO3 with β-chlorovinyl ketones, prepared regioselectively by the reaction of 2-acetylcyclo- pentanone-type diketones with PPh3-CCl4 in 73–78% yield, to afford 2-alkyl (aryl)-pyrimidines annelated with cyclopentane derivatives in 79–87% yields.

Spectroscopic Study of a Single Vacuum-Arc Cathode Spot

The cathode-spot plasma in spark and arc stages of a vacuum discharge was studied spectroscopically. A single spot was generated with high reproducibility in a gap under ultrahigh-vacuum conditions with a liquid-metal cathode of GaIn alloy. The self-breakdown of the vacuum gap resulting in a short discharge of less than 100 ns as well as a discharge over and up to 3 mus has been considered. The combination of a 0.5-m spectrograph with a streak camera enabled observation of spot evolution with a time resolution in the nanosecond range. Applying the streak camera as an image converter, time-integrated spectra resolved in the direction along the arc axis have been obtained. Limits concerning wavelength and time resolution as well as the emission intensity are discussed. Spectral lines of Ga and In atoms and single- and double-charged ions have been observed simultaneously. At the beginning of the discharge, ionic lines of higher charge state and wide line broadening dominate the spectrum. With a delay of several hundreds of nanoseconds, atomic lines appear and fall down in intensity to a much lesser degree than the ionic lines. Hence, atomic lines finally dominate in the arc stage of the discharge.

Observation of the Plasma Plume at the Anode of High-Current Vacuum Arc

Stable and bright plumes with a distinct and bright shell are observed at the anode of the high-current vacuum arc burning during 10 ms at a current of up to 15 kA in peak. A plume is attached to a hot spot at the anode. The substance inside a plume is almost dark. Light from a plume shell is emitted mostly by neutral atoms. A distinct bright shell is surrounded by substances emitting light in ion lines. Appearance of plumes looks to be a result of the interaction between cathode and anode jets. Plume dimensions depend inversely on both arc current and arc voltage, which makes plumes small and inconvenient for observations except as near current zero. Anode plumes are recognized on copper-chromium electrodes to be a stable object. However, similar objects on pure copper are much less stable and appear only at heat-insulated liquid protrusions and droplets flying in a gap. This fact indicates the evaporation rate to play a key role in appearance of plumes. In addition, the evaporation rate of a plane copper-chromium surface under high-current vacuum arc is supposed to be as high as that of heat-insulated liquid copper protrusions and droplets.