Effect of solvent on the conformational equilibrium of 2-substituted 5,6-benz-1,3-dithiepins

Conclusions From an analysis of the variation of¹ H NMR spectra with temperature it has been shown that 2-substituted 5,6-benz-1,3-dithiepins exist in solution in the chair-e and boat-e conformations, the equilibrium between which depends considerably on the nature of the solvent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 545–548, March, 1987.The authors wish to thank E. N. Klimovitskii and D. Yu. Strel'nik for submitting compound (III).     

Steric structure of phosphorus-containing heterocycles Communication 36. 2-dialkylamino-1,3,2-dioxaphosphepines with tetracoordinated phosphorus

Conclusions In conformity with the data of¹H NMR, DM, and the Kerr effect for 2-dialkylamino-2-oxo(thiono, seleno)-1,3,2-dioxaphosphepines, a conformational equilibrium of two forms of twist and chair with an equatorial dialkylamino group is observed in solutions. The equilibrium is displaced in favor of the latter.Then the products were crystallized after removing a part of the solvent in vacuo.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 799–803, April, 1985.     

Influence of the solvent on the activation parameters of the conformational conversions of 2-substituted 1, 3-dithia-5,6-benzocycloheptenes

Conclusions The enthalpy and entropy of activation of the chair(e)-boat(e) interconversion for 2-substituted 1,3-dithia-5,6-benzocycloheptenes depend significantly on the type of the solvent, whereby the changes in the enthalpy of equilibrium and of activation are not determined by the same factors when the solvent is changed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1253–1256, June, 1989.     

Measurement of the velocity profile in liquid streams of large volumes using a laser Doppler velocimeter

The use of the laser Doppler velocimeter (LDVM) in fluid mechanics already has a solid past history and work on its development is proceeding rather intensively [1, 2], This method has been used successfully to measure various parameters of flows in channels or chutes of small size [3–6]. Fundamental difficulties due to possible local variations in the index of refraction along the path of the laser beam [7], in addition to technical difficulties, have not been eliminated for its use in other cases of practical importance, particularly in basins or reservoirs of large size. The aim of the present paper is the investigation of the velocity structure of streams in large volumes using an LDVM on the example of a turbulent submerged water jet. In order to estimate the effect of the thickness of the water layer on the applicability of the method we tested three schemes: based on direct [8] and back scattering [9] and a scheme with reflection of forward-scattered light from a mirror [10]. The results of the investigation of a submerged turbulent jet using an LDVM are presented.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 170–173, September–October, 1977.     

Stereochemistry of seven-membered heterocycles: XLVI. Synthesis and dynamic <Superscript>13</Superscript>C NMR spectroscopy of spiro[cyclohexane-1,4′-[3,5]dioxabicyclo[5.1.0]octanes]. DFT calculations of structurally related formaldehyde and acetone acetals

Spiro[cyclohexane-1,4′-[3,5]dioxabicyclo[5.1.0]octanes] were synthesized, and their conformational behavior was studied by dynamic ¹³C NMR spectroscopy. Anancomeric displacement of conformational equilibrium toward two nonequivalent twist conformers with close energies was revealed. The relative Gibbs energies ΔG ^o and enthalpies of formation ΔH ^o of twist and chair-like conformers with endo and exo orientation of the three-membered ring of structurally related formaldehyde and acetone acetals were calculated in terms of the density functional theory at the B3LYP/6-31G(d,p) level. Like spiro-cyclohexane analogs, they were shown to have a non-chair conformation.     

Effect of surface magnetism of solid-state substrates on the NMR of liquid 3He

The results of investigations of the longitudinal relaxation rate of the nuclear spins of liquid helium-3 in contact with finely dispersed LiYF₄ dielectric powders with various degrees of filling of the microcracks on the crystal surface by water molecules are reported. It is found that exchange correlations appear between paramagnetic defect centers on the surface as a result of spin-density transfer via the molecular orbitals of oxygen in the water molecule. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 7, 503–509 (10 April 1999)     

Emission spectrum of concentrated dye solutions excited by high-power laser radiation

Emission spectra of concentrated (~10¹⁸–10¹⁹ cm^–3) ethanol solutions of Rhodamine C excited by high-power (~10²⁵–10²⁶ cm^–2s^–1) laser radiation were measured. The emission spectrum consists of two narrow bands (with half-widths of ~200–300 cm^–1). The long-wavelength band was interpreted as cooperative spontaneous emission, and the short-wavelength band was assigned to the amplified spontaneous emission. The ratio of their intensities depends on the dye concentration and the pump power density. The ratio of band intensities is assumed to be determined by the dephasing rate of excited molecules responsible for cooperative spontaneous emission.