Interpretation of Π→Π electronic transmissions in the absorption spectra of flavone and its hydroxy derivatives

The electronic spectra of flavone and its 4′-, 3-, 5-, and 7-monohydroxy derivatives have been calculated by the standard Pople-Pariser-Parr method. The contributions of the fragments to the total molecular excitation have been calculated. It has been shown by computer modeling that the electronic transitions of the flavone spectrum can be reduced to the corresponding transitions of the spectrum of chromone, but not of chalcone. A graphical analysis has been performed of the experimental absorption curves. A four-component system of individual bands in the 230–400 nm region is proposed. Their mutual superposition or resolution is responsible for the features of the spectra of hydroxy-substituted flavones.     

Ultraviolet absorption of flavonoids IV. Protonation constants of some monohydroxy flavones

Summary 1. The protonation constants of flavone, 3-hydroxyflavone and its methyl ether, and 7-, 5-, and 4-hydroxyflavones have been determined by a spectrophotometric method.2. It has been shown that the basicities of the monohydroxyflavones change fundamentally according to the position of electron-donating substituents in the molecule.Irkutsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 25–28, January–February, 1973.     

Circular dichroism of acetylated methyl glycosides

The circular dichroism (CD) spectra of a number of acetylated methyl glycosides, from mono-to tetra-O-acetates, have been obtained. The signs of the CD maxima of the n-* transitions (210–215 nm) of the O-acetate groups have been predicted, and these predictions coincide with the figures obtained experimentally.Pacific Ocean Institute of Bioorganic Chemistry of the Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 54–56, January–February, 1980.     

First electronic transitions in compounds with the perimeter π-system

In the Pariser-Parr-Pople approximation, an analysis has been made of the first -electron transitions in neutral and charged [N]annulenes with a closed shell. The influence of the ratio of numbers of -electrons and atoms in the annulene on the spectrum of the annulene has been examined critically. A similarity of the spectra of [N]annulenes and polymethine dyes has been noted.Deceased.Institute of Organic Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 4, pp. 493–499, July–August, 1991. Original article submitted February 8, 1988.     

Quantum chemical study of 2-substituted 4-oxo-and 4-thioxospiro(benzo[h]quinazoline-5,1′-cycloalkanes) in alkylation reactions

The steric and electronic structures of 2-substituted 4-oxo- and 4-thioxospiro(benzo[h]quinazoline-5,1-cycloalkanes and their deprotonated forms have been calculated by the semiempirical PM-3 quantum chemical method. Using the conclusions of limiting orbital theory, a quantum chemical explanation has been derived, based on the calculations made, for the selectivity of alkylation of the systems investigated.A. L. Mndzhoyan Institute of Fine Organic Chemistry, Armenian Academy of Sciences, Erevan 375014, Armenia. M. V. Lomonosov Moscow State University, Moscow 119899, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1118–1124, August, 1998.     

Configuration of stereoisomers of naringenin 5-glucoside present in flamin

The configurations of the C-2 chiral centers of the stereoisomers of naringenin 5-glucoside isolated from flamin by HPLC have been established by the method of circular dichroism. One of the stereoisomers is (–)-2S-naringenin 5-glucoside and the other has been characterized as a molecular compound containing the 5-glucosides of (+)-2R- and (–)-2S-naringenins in a ratio of 2:1.1st I. M. Sechenov Moscow Medical Institute. M. V. Lomonosov Moscow State University. All-Union Scientific-Research Institute of Drug Chemistry and Technology, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 185–188, March–April, 1989.     

Synthesis,spectroscopic and magnetic properties of methoxo- bridged copper(II) complexes with 2-amino-4-methylpyridine as the ligand

Three new methoxo-bridged copper(II) complexes with 2-amino-4- methylpyridine as the ligand have been synthesized and characterized by elemental analyses, FTIR and electronic spectra, and by their magnetic properties. The complexes exhibit strong antiferromagnetic interactions at room temperature. The u.v.-vis spectra exhibits three absorption bands, which can attributed to d–d, L–M and –* transitions. The i.r. spectra indicates Cu2O2 ring vibrations in the 580–530cm–1 range. The magnetic properties of the [Cu2(2-amino-4-methylpyridine)4(O- Me)2](ClO4)2 complex has been investigated in the 5–270K range and a singlet-triplet energy gap (–2J) of 67cm–1 was observed. All complexes in the solid state are e.p.r.-silent and show no triplet spectrum; in fact a weak signal due to a monomeric impurity are observed. Frozen solution e.p.r. spectra suggest that the complexes dissociate when dissolved in DMF or DMSO.     

Xα–DV Modeling of Photoionization and Electronic Absorption Spectra of Cobalt tris–Acetylacetonate

Ionization energies, excited state energies, and oscillator strengths of electron–dipole transitions are calculated within the framework of the SCF–X–DV quantum–chemical model of the Co(HCOCHHCO)₃ model complex in order to interpret the photoionization and electronic absorption spectra of cobalt tris––diketonate. It is shown that the sequences of ionization and excitation energies calculated in the transition state approximation do not significantly differ from the sequence of energies estimated in the frozen MO approximation. The model absorption spectrum with a correction of 1.9 eV applied to the energy of the vacant ₄ ^* orbital is in good agreement with our gas–phase absorption spectrum of Co(acac)₃.     

13C NMR spectra of handelin and its derivatives

The¹³C spectra of the diguaiane lactone handelin (I), deacetylhandelin (II), handelin diacetate (III), and deacetyldehydrohandelin (IV), and also cumambrin A (V) — a known sesquiterpene lactone that is a component part of the molecule of the compound (I) and is isolated together with it from a single source — have been studied. The identification of the resonance lines was based on a comparison with one another of the¹³C NMR spectra of compounds (I–IV) and (V) obtained under conditions of complete and partial decoupling from protons, and an analysis of the chemical shifts of certain carbon atoms of the model lactone cumambrin A and their comparison with the analogous parameters of handelin and its derivatives. The -, -, and -contributions of the neighboring groups to the chemical shifts of the carbon atom considered, and, in individual cases, the contributions due to steric factors, were also taken into account. A complete assignment of the lines of the spectra has been made on the basis of the comparative consideration performed.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 329–334, May–June, 1979.     

Anthraquinones of the lichenAsahinea chrysantha

From a hexane extract of the dry lichen we have isolated six anthraquinones: chrysophanol (I), islandicin (II), cynodontin (III), emodin (IV), a tetrahydroxymethylanthraquinone (V), and a pentahydroxymethylanthraquinone (VI). The structures of (I) and (IV) were confirmed by direct comparison with authentic samples. The structures of (II) and (III) were established by the aid of UV, IR, PMR, and mass spectra. Pigments (V) and (VI) were isolated from a carbonate extract. Pigment (V): mp > 320°C; UV spectrum (nm) 258, 283, 310, 447, 500, 533; mass spectrum: 286 (M⁺ 100%), 270, 258, 257, 241, 229, 216, 213, 212, 211, 201, 161, 155, 137, 115, 105, 97. Pigment (VI): mp 315°C; UV spectrum (nm): 247, 261, 302, 500, 540, 565, 578; IR spectrum (cm^–1): 1587, 3492; mass spectrum: 302 (M⁺, 100%), 286, 274, 245, 228, and the metastable ions 248.6, 219.1, and 192.5. The positions of the -hydroxyls in the molecules of (V) and (VI) have not been definitively established.Pacific Ocean Institute of Bioorganic Chemistry of the Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 160–165, March–April, 1980.