UV absorption spectra of 3-aminorhodanine derivatives

3-Aminorhodanine condenses readily with isothiocyanates to form unsymmetrical thioureas of the rhodanine series. The UV spectra of arylidene derivatives of 3-aminorhodanine consist of four bands: a short-wave band with a maximum up to 242 nm, a “thioamide” band with a maximum at 264–290 nm, a “dithiocarbonate” band with maxima at 290–370 nm, and a long-wavelength K band with maxima at 310–520 nm. The K absorption band is the most characteristic band for the arylidene derivatives of 3-aminorhodanine, and the maxima for 3′,5-diarylidene derivatives are generally shifted to the short-wave region, while the maxima for the 5-monoarylidene derivatives are usually shifted to the long-wave region.     

Synthesis and reactions of oxo and thio derivatives of 1,3-thiazane

The reaction of 1,3-thiazane-2,4-dithione with amino compounds and diazonium salts has given the corresponding 4- and 5-substituted derivatives. The high reactivity of the thione group in position 4 has been noted. The optimum conditions for azo coupling have been found.For part II, see [1].     

Temperature effect upon the UV absorption spectra of aniline derivatives

Cooling of aromatic amines in nonpolar media shows a disappearance of the absorption CT band. This disappearance suggests the existence of a different conformation of these molecules in the stiffening range.     

Synthesis and properties of derivatives of 4-imino-l,3-thiazane

The reaction of thiazane-2,4-dithiones with thiosemicarbazide and p-nitrophenylhydrazine has given the corresponding derivatives of 4-imino-1,3-thiazane. The 4-thiosemicarbazones obtained have one absorption maximum at 247–255 nm and a characteristic inflection at about 300 nm; the 4-p-nitrophenylhydrazones are characterized by three maxima in the 238–265, 303–316, and 400–405 nm regions.     

Electronic absorption spectra and protolysis of 4- and 5-azaindan-1,3-diones

The protolytic equilibria in a series of 2-aryl-substituted 4- and 5-azaindan-1,3-diones and the corresponding N-methylbetaines and 5,6-benzo analogs were studied by spectrophotometry. The substantial difference between the 4- and 5-aza derivatives is explained by the different effect of the anionic system on the Tr-electron density and the reactivities of the nitrogen atoms in the 4 and 5 positions. The protonation and deprotonation constants of the dipolar ions correlate linearly with the constants of the substituents in the 2-phenyl ring. In the case of 5,6-benzo-4-azaindan-1,3-diones, the keto group of the azaphthaloyl ring is protonated along with the dipolar ion in strongly acidic media.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1382–1386, October, 1972.     

Electron impact mass spectra of 2-hydrazono-1,3-thiazolidin-4-one derivatives

Mass fragmentation of 2-hydrazono-1,3-thiazolidin-4-ones is dominated by two processes, namely cleavage of the hydrazone fragment with accompanying proton transfer from the latter to the thiazolidine ring, and cleavage of a hydrazone imide residue.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1117–1119, August, 1990.     

Synthesis and absorption spectra of thienylphenylpropenol derivatives

Fourteen thienylphenylpropenol derivatives containing substituents of varying electronic nature were synthesized. IR and NMR spectroscopy established that the , -unsaturated alcohols obtained belong to the trans series. The electronic and PMR spectra of the alcohols in neutral and acidic solutions were studied. A correlation was found between the chemical shifts of the proton of the alcohol hydroxyl group and the shifts of the wave numbers of the long-wave absorption maxima, and the Hammett constants.Translated from Khimiya Geterotsilicheskikh Soedinenii, No. 12, pp. 1605–1608, December, 1970.     

Synthesis and UV absorption spectra of 5-isoxazolepolyene aldehydes

The preparation and UV spectra of a series of 5-isoxazolepolyene aldehydes are reported and discussed. A linear relationship between the λ²_max and the number of double bonds was found. A simple LCAO-MO calculation on this series of compounds and on the corresponding 2-furanepolyene aldehydes was carried out to interpret the experimental data.     

Conformational effects in UV absorption spectra of tetrasilanes

UV absorption of cyclic carbosilanes (SiMe₂)₄(CH₂)_n, N = 1–4 (1–4), and Si₄Me₁₀ (5) provides an experimental counterpart to the singlet transition energy and intensity correlation diagrams for the syn-anti conformational transformation in tetrasilane. A new third transition is found between the two previously known singlet transitions. Transition energies are nearly independent of the dihedral angle, while intensities vary widely. All trends agree with CIS/3–21G^*//HF/3–21G^* calculations. The Sandorfy C and ladder C models of σ conjugation fail to describe electronically excited states of tetrasilane, since they do not consider the lateral bonds to substituents.     

Synthesis and reactivity of ethoxyvinyl derivatives of 1,3-dioxolanium salts

2-(-Ethoxyvinyl)dioxolanium salts were obtained by reaction of ortho esters with 2,4,4,5,5-pentamethyl-1,3-dioxolanium perchlorate in acetic anhydride. Alkaline hydrolysis of 2-(-ethoxyvinyl)-4,4,5,5-tetramethyl-1,3-dioxolanium perchlorate leads to the corresponding ,-unsaturated aldehyde. Substituted 2-(-aminovinyl)-1,3-dioxolanium perchlorates are formed by reaction of this salt with aromatic amines, amino acids, and urea. These perchlorates readily split out perchloric acid in alkaline media to give Schiff bases. The charges and electron densities were calculated for the 2-(-methoxyvinyl)-1,3-dioxolanium cation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1614–1617, December, 1973.     

Electronic absorption spectra of some benzenechromiumtricarbonyl derivatives

Absorption spectra of some arenechromiumtricarbonyl derivatives have been studied. The linear dependence of the extinction coefficient of the longer wavelength absorption band on σ_p⁺ constants of substituents in a benzene ring has been established and it has been shown that a longer wavelength band is a band of intramolecular charge transfer from the central chromium atom to π-bonded arene.     

Singlet and triplet transitions in UV absorption spectra of pentacene

The UV absorption spectrum of pentacene in hexane solution and the diffuse UV reflectance spectrum for its solid sample have been obtained. A spectral band due to structural features resulting from intermolecular interactions in the solid state was detected for the solid sample at the energy of 1.51 eV. The types of detected electronically excited states for pentacene have been determined, and dominating electronic configurations have been interpreted using TD B3LYP/6-31G quantum-chemical calculations. The types of pentacene occupied and unoccupied molecular orbitals involved in electronic transitions have been determined from published photoelectron spectroscopy data for pentacene with the preliminary assignment of the relevant photoionization bands using the B3LYP/6-31G calculation method.     

Role of 2-oxo and 2-thioxo modifications on the fragmentation reactions of the histidine radical cation

The fragmentation reactions of the radical cations, M(·+), of histidine, 2-oxo-histidine and 2-thioxo-histidine were examined using a combination of experiments performed on a linear ion trap and density functional theory (DFT) calculations at the UB3-LYP/6-311++G(d,p) level of theory. Low-energy collision-induced dissociation (CID) on [Cu(II)(terpy)(M)](2+) complexes, formed via electrospray ionisation, produced the radical cations in sufficient yield to examine their unimolecular chemistry via an additional stage of CID. The CID spectrum of the radical cation of histidine is dominated by loss of water with the next most abundant ion arising from the combined loss of H(2)O and CO. In contrast, the CID spectra of the radical cations of 2-oxo-histidine and 2-thioxo-histidine are dominated by the combined loss of CO(2) and NH=CH(2). The observed differences are rationalised via DFT calculations which reveal that the barrier associated with loss of CO(2) from the histidine radical cation is higher than that for loss of H(2)O. In contrast, the introduction of an oxygen or sulfur atom into the side chain of histidine results in a reversal of the order of these barrier heights, thus making CO(2) loss the preferred pathway.     

TD-DFT investigation of the UV spectra of pyranone derivatives

The UV absorption spectra of more than 80 substituted coumarins and chromones have been investigated with the PCM-TD-DFT theoretical scheme using three hybrid functionals (O3LYP, B3LYP, and PBE0) and taking into account methanol or ethanol solvation effects. For most of the studied derivatives, there are at least two allowed excited states presenting a strong oscillator strength in the UV region. The first allowed excitation is associated to a HOMO-LUMO transition whereas the second corresponds to a transition from the HOMO-1 to the LUMO. Both involve a charge transfer from the benzenic cycle to the pyranone moiety. Statistically treating the PBE0 results allows a prediction of the lambda(max) with small standard deviations: in methanol, 6 nm (0.07 eV) for the first excitation (lambda(max)(1)) and 5 nm (0.08 eV) for the second one (lambda(max)(2)), whereas in ethanol 6 nm (0.08 eV) for (lambda(max)(1)) and 6 nm (0.13 eV) for (lambda(max)(2)).     

Infrared absorption spectra of some C-halogenated 1, 2, 4-triazole derivatives

The IR absorption spectra of 3(5)-halo and 3, 5-dihalo derivatives of 1, 2, 4-triazoles and of their potassium and silver salts as solids in the 3500-400 cm^–1 range were studied. The characteristic absorption bands of the triazole ring and the C-H and N-H bonds were established.     

IR and electronic absorption spectra and structures of 3-hydroxy-4-phenylazo-quinoline and 4-hydroxy-3-phenylazoiso-quinoline derivatives

It was shown by an analysis of the IR and electronic absorption spectra that 3-hydroxy-4-azophenylquinoline derivatives exist primarily in the azo form in organic solvents, whereas 4-hydroxy-3-phenylazoisoquinoline derivatives exist primarily in the quinone-hydrazone form. The introduction of electron-acceptor groups into the para position of the phenyl ring of 3-hydroxy-4-azophenylquinoline shifts the tautomeric equilibrium to favor the formation of the quinonehydrazone form. It is shown that the band at 550 nm in electronic spectrum of this compound is related to the n ^* transition of the unshared pairs of electrons of the nitrogen atoms of the azo groups.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1522–1524, November, 1974.     

Ultraviolet absorption spectra of some pyridine and nicotine derivatives

Summary Comparison of the ultraviolet spectra of nicotine, N-methylanabasine, and their N-oxides shows that though the characters of the absorption of compounds containing the N-oxide group in the aromatic part of the molecule, on the one hand, and in the hydrogenated part, do not differ considerably, they are nevertheless sufficiently specific for a clear distinction to be drawn.For Communication 3 see [1].