Dipole moments of thiophene analogs of chalcones and their vinylogs

The dipole moments of 25α, β unsaturated ketones of the thiophene series are measured in benzene at 25°, and their most probable coplanar conformations established. For the systems studied it is shown that, in the static state, the 2-thienyl group exhibits an electron-donating effect, greater than those of 2-furyl and phenyl. Introduction of electron-donating and electron-accepting substituents into the molecule of 1-(thienyl-2)-3-phenylpropenones as well as shift of the carbonyl group away from the aryl one towards the heterocyclic ring, leads in general to an increase in dipole moment. A linear relationship is found for the changes in dipole moment of isomeric thiophene ketones due to electron-donating substituents. Dipole moments of propen-3-ones correlate satisfactorily with Hammett σ parameters for substituents, and intermolecular distances.     

Comparative investigation of the intramolecular interaction of the chromophores in diketones and dihydroxydicarbonium and dicarbonium ions

The intramolecular interaction of the chromophores in the systems of the dichalcone (I) and its dihydroxydicarbonium (II) and dicarbonium (III) ions with the general formula

Drag coefficient of an absorbing plate set transverse to a flow

Supersonic flow past an absorbing surface is considered. The flow past a plate set transverse to the oncoming stream is calculated on the basis of a model kinetic equation. It is found that the dependence of the drag coefficient on the surface adsorption coefficient qualitatively changes on transition from the free molecular to the continuum flow regime. It is shown that in dense media a drag coefficient maximum is reached at total gas absorption by the surface. Under these conditions the surface interacts with the undisturbed stream. The effect of the extent of the plate-produced disturbance region on the plate drag is investigated.     

Alkylation of 3‐Phenyl‐1H‐pyrazolo[4,3‐c] quinoline: Theoretical Analysis of Regioselectivity

The interaction of 3‐phenyl‐1H‐pyrazolo[4.3‐c]quinoline with alkylating agents in the presence of NaH leads mainly to N1‐substituted derivatives. The regioselectivity of the reaction has been studied using AM1 semi‐empirical calculations in the isolated molecule approximation.     

Methane Pyrolysis for Hydrogen Production: Specific Features of Using Molten Metals

Russian Journal of Applied Chemistry - Published data on noncatalytic pyrolysis of natural gas in molten metals are analyzed. The most illustrative results obtained in the past two decades are...     

Electronic absorption spectra or carbonium and dicarbonium ions containing heterocyclic rings with a biphenylene base

An analysis has been made of -^* -electronic excitations of carbonium and dicarbonium ions obtained by the interaction of concentrated sulfuric or fluoboric acid with alcohols or glycols containing a heterocyclic bridge structure, i.e., nuclei of dibenzofuran, dibenzothiophene, carbazole, and N-methylcarbazole; this analysis has been aimed at establishing a correlation of their structure and spectral characteristics. From an analysis of experimental data, calculated results, and indexes quantitatively characterizing the structure of the -^* -electronic excitations, it has been established that there are four electronic transitions in the visible region of the electronic absorption spectrum of the carbonium ions. The long-wave, intense band of the spectrum is due to superposition of intense (p-type) and weak (-type) transitions proceeding from corresponding excitations of the heterocyclic fragment. In the electronic spectra of the dicarbonium ions, a doublet of p-transitions is clearly manifested. It has been shown that the interaction of chromophores through the bridge structure increases by a factor of approximately 1.8 when the change is made from dibenzofuran to dibenzothiophene, carbazole, and Nmethylcarbazole; in comparison with the corresponding dihydroxycarbonium ions, the degree of interaction of the chromophores is greater by a factor of approximately 1.5.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 284–291, May–June, 1990.     

Electronic structure and absorption spectra of dicarbonium ions containing bridging groups

The electronic structure and spectral characteristics of polymethines with the general formulas [CH₃-M-C₆H₄-(CH)_n-C₆H₄]⁺ X^– (C) and [R-C₆H₄-(CH)_n-C₆H₄-M-C₆H₄-(CH)_n-C₆H₄-R]²⁺ 2X^– (D) were investigated. The absorption spectra of the dicarbonium ions were treated in terms of the theory of intramolecular interaction of the chromophores. By analysis of the experimental data and calculated data, obtained by the PPP method, it was established that the long-wave splitting in compounds of type D increases in the series M= (CH₂)₂ CH₂, O, S, NCH₃, does not depend on the electronic symmetry of the parent compounds (C), decreases with increase in the length of the polymethine chain (n), and decreases with increase in the electrondonating characteristics of the substituents (R). The energy of intramolecular interaction of the chromophores is separated into dipole-dipole, resonance, and exchange components, a method is proposed for their quantitative assessment, and the effect of various structural factors on them is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 419–427, July–August, 1988.     

The nature of the bands of the electronic absorption spectra of acid solutions of aromatic α,β-unsaturated ketones

The electronic absorption spectra of 34 unsaturated ketones were measured in solutions of 93% sulfuric acid. The curves of the absorption of the hydroxycarbonium ions formed as a result of protonation of the investigated compounds in sulfuric acid solutions, are characterized by the presence of two intense bands of the -^* type in the region of 330–630 nm. The nature of the bands of the investigated compounds is discussed on the basis of the calculated data, obtained according to the PPP method, with an estimation of the localization and charge transfer numbers of the electronic transitions on individual fragments. According to the data of calculation and graphical analysis it was shown that the long-wave band in a series of derivatives of diphenylmethane and diphenyl oxide (I, II) should be assigned to the protonated cinnamoyl (C) fragment, while the second (short-wave) band should be assigned to the protonated acetophenone (A) fragment. The long-wave band in the series of derivatives of diphenyl sulfide, diphenylamine, and N-methyldiphenylamine (III–V) was assigned to the protonated acetophenone fragment. The resonance, dipole-dipole and exchange interactions of the fragments A and C is analyzed, and an attempt was undertaken to distinguish various types of interactions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 321–328, May–June, 1985.