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Keto-enol and amine-imine tautomerism and equilibria with trans-conformers are characteristic of 1-(alkyl,aryl)amino-4-hydroxy-9,10-anthraquinones. Amino forms possess 1,10- and 1,4-, but not 9,10-quinoid structure. Various tautomeric and conformeric transformations are in competition. The outcome of this competition may be studied by the correlation analysis of electron absorption spectra but it would be possible to understand the causes of changes in the direction of the competing transformation only in the case when each action on the substance would be accompanied with establishing the corresponding alterations in its tautomeric composition.

Neutral [EuL3Phen] complexes were synthesized by the reaction of EuCl3 with heterocyclic diketones-1-(1,5-dimethyl-1H-pyrazol-4-yl)-4,4,4-trifluoro-1,3-butanedione and 4,4,5,5,6,6,6-heptafluoro-1-(1-methyl-1H-pyrazol-4-yl)-1,3-hexanedione—and 1,10-phenanthroline (Phen) in an aqueous alcohol solution in the presence of NaOH. The reaction of GdCl3 with the same diketones under analogous conditions, but without adding 1,10-phenanthroline, yielded [GdL3(H2O)2] complexes. The composition of the complexes was determined by elemental analysis, and their optical and luminescent properties were examined.

Based on the example of 1,4,5,8-tetraamino-9,10-anthraquinone, a method is described for establishing the tautomeric compositions and sequences of tautomeric transformations that occur in known samples of quinones. An analysis of electronic absorption spectra shows that this substance is a dynamic equilibrium mixture of 4,5,8,9-tetraamino-1,10-anthraquinone and the imines tautomeric to it. The tautomeric compositions of different samples of matter differ and can contain 1,4,8-triamino-5-hydroxy-9,10-anthraquinone-10-imine, 4,8,9-triamino-10-hydroxy-1,5-anthraquinone-5-imine, 5,8-diamino-4,9-dihy-droxy-1,10-antraquinonediimine, and 8,10-diamino-5,9-dihydroxy-1,4-antraquinonediimine. Tautomeric equilibrium shifts can accompany not only chemical reactions but physical processes as well, so any investigation of the properties of substances without establishing their tautomeric compositions would be incorrect.

Compounds widely known as 1,4-bis(alkylamino)-9,10-anthraquinones are in fact neither individual substances nor substituted 9,10-anthraquinones but equilibrium mixtures of tautomers. Their aminoimine tautomeric transformations follow the sequence 4,9-bis(alkylamino)-1,10-anthraquinones ↔ 9-alkylamino-4-(alkylimino)-10-hydroxy-1,4-dihydroanthracen-1-ones ↔ N 1,N 10-dialkyl-4,9-dihydroxy-1,10-dihydroanthracene-1,10-diimines.

3-amino-4-hydroxy benzenesulfonamide and its hydrochloride have been isolated in the crystalline state. Their crystal and molecular structures are determined by X-ray diffraction. The equilibrium between neutral tautomeric forms of the 3-amino-4-hydroxy benzenesulfonamide molecule is studied within the approximation of density functional theory (B3LYP/aug-cc-pVDZ). The constants of acid-base equilibrium of 3-amino-4-hydroxy benzenesulfonamide are deter-mined using spectrophotometry.

Complexes of copper(II), nickel(II), and cobalt(II) chlorides and bromides with 2-phenyl-4-(piperidyl-1)-anthra[1,2-b]pyridine-7,12-dione (L1) and 2-[phenyl-4-(octylamino)-anthra[1,2-b]pyridine-7,12-dione (L2) were synthesized from neutral and acidic media. The molecular and crystal structure of 2-phenyl-4-(piperidyl-1)-anthra[1,2-b]pyridine-7,12-dionium hexabromodicuprate(II) (HL1)2[Cu2Br6] was determined by X-ray diffraction analysis. The spectral characteristics of L1 and L2 and their complexes are presented. Formation of their complexes in solutions was studied.

Structure and amino-imine tautomerism of α-aminoanthraquinones, 1,5-and 1,8-diaminoanthraquinones, as well as 1,4,5-triamino-9,10-anthraquinones was studied. We found that in the study of properties of the compounds prone to tautomeric transformation the tautomeric composition should be taken into account.

The fine structure of the πl,π*-absorption of hydroxyanthraquinones solutions in sulfuric acid arises due to the existence of the protonated forms as equilibrium mixtures of tautomers and conformers distinguished by the positions of the π-bonds, charges, and the number of intramolecular hydrogen bonds. Using quantum-chemical calculations and correlation analysis of the absorption spectra tautomers were identified of mono- and dications of 1,4,5-trihydroxyanthraquinone of 9,10-, 1,4-, and 1,10-isomeric structure. For 1,4,5,8-tetrahydroxyanthraquinone 9,10-, 1,4-, 1,10-, and 1,5-isomeric mono- and dications and their conformers were found.

The reaction of Tb(NO3)3 · 6H2O with 1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)-1,3-propanedi-one (HL) and 1,10-phenanthroline (Phen) in the presence of NaOH in a water-alcohol medium afforded the neutral complex [Tb(L)3(Phen)] (I). The unstable adduct [Tb(L)3(Phen)] · 0.4 MeCN (II), whose structure is studied by X-ray diffraction analysis, is obtained from an acetonitrile solution. The crystals of compound II at 100 K are triclinic, a = 11.2508(13), b = 11.4246(14), c = 22.486(3) A, α = 96.522(2)°, β = 91.578(2)°, γ = 110.073(2)°, V = 2690.3(5) A3, space group P $$\bar 1$$ , Z= 2, R = 0.0433. The complex is characterized by the green luminescence (λexc = 380 nm, λem = 550 nm).

Chemistry of 9,10-anthraquinones is considered as chemistry of isomeric anthraquinones existing in dynamic equilibrium with each other. Diversity of electronic absorption spectra of the same compounds is determined by tautomeric transformations. Alizarin exists as equilibrium mixtures of tautomers and conformers having 9,10- and 2,9-quinoid structures. Qualitatively different compositions are inherent not only to samples of alizarin prepared or purified by different methods but also to different solvates of the same sample.

Reaction of Eu(NO3)3·6H2O with 1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)-1,3-propanedione (HL) in the presence of NaOH affords the complex compound [Na(H2O)4] [EuL4]·0.775CH2Cl2 (I). The spectral (UV, IR, 1H NMR spectroscopy), and thermo-luminescent (TG-DSC-MS) properties of the complex I, as well as its fragmentation at the laser desorption ionization (LDI-MS) were studied.

A reaction of Eu(NO3)3·6H2O with the novel heterocyclic ligand 1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)propane-1,3-dione and 1,10-phenanthroline in the presence of NaOH gave the complex Eu(phen)L3·5CH2Cl2. The crystal structure of the complex was determined by single-crystal X-ray diffraction. The coordination polyhedron {EuO6N2} is a tetragonal antiprism. The complex shows bright orange-red luminescence in both the solid state and solution.

Solubilities in the NaOH-TiO2 · H2O-H2O system at 25°C were studied. The solubility isotherm was found to have two maxima. The formation of two compounds, Na2Ti5O11 · 10H2O and Na2Ti3O7 · 7H2O, was established.

Nine complexes of copper(II), cobalt(II), Ni(II), and Zn(II) chlorides with naphtho[1,2,-c][1,2,5]oxadiazol-9-ol (HL1), naphtho[1,2-c][1,2,5]thiadiazol-9-ol (HL2), and naphtho[1,2-c][1,2,5]selenadiazol-9-ol (HL3) have been synthesized, isolated in the crystalline state, and studied by physicochemical methods. The composition of the complexes in solutions as been determined and their stability constants have been calculated from spectrophotometric data. The electronic structures of the ligands and complexes have been calculated by quantum-chemical methods. The crystal and molecular structure of HL2 has been determined by X-ray crystallography.

Benzo[4,5]imidazo[1,2-c]quinazolin-6-one and 10-carboxybenzo[4,5]imidazo[1,2-c]quinazolin-6-one were isolated in the crystalline state and studied by X-ray diffraction. The crystal and molecular structures of these compounds were determined by X-ray diffraction. The energy characteristics of the tautomeric and ionic forms were calculated by the quantum-chemical PM3 method.

[Na(H2O)4][EuL4] · 0.775CH2Cl2 (I) has been synthesized by the reaction of Eu(NO3)3 · 6H2O with 1,3-bis(1,3-dimethyl-1H-pyrasol-4-yl)-1,3-propanedione (HL) in the presence of NaOH. Its crystal structure has been solved by X-ray diffraction analysis. Crystals are tetragonal; a = 16.2401(5) A, c = 11.9113(4) A, V= 3141.50(17) A3, ρcalcd = 1.427 g/cm3, μ(MoKα) = 1.140 mm−1, space group P4/n, Z = 2. The structural units forming a crystal of compound I are [EuL4]− complex anions, [Na(H2O)4]+ cations, and CH2Cl2 molecules. The coordination polyhedron of the Eu atom is an Archimedean antiprism formed by the O atoms of four bidentate chelate ligands L−.

Eight aluminum, cobalt(II), copper(II), cadmium, samarium(III), and europium(III) complexes with 2,4,6-tris(N,N-dimethylaminomethyl)phenol (HL) were isolated in the crystalline state and studied by physicochemical methods (IR and UV-Vis spectroscopy, potentiometry). The complexation processes of singly, doubly, and triply charged metal ions with HL were studied by spectrophotometry and potentiometry, the composition of complexes was determined, and the stability constants were calculated. The crystal and molecular structures of 2,4,6-tris(N,N-dimethylaminomethyl)phenol trichloride and trinitrate H4L(NO3)3 · H2O and H4LCl3 · 3H2O were studied by X-ray diffraction.

The products of reaction of α-hydroxyanthraquinones with boric acid are mixtures of 9,10-, 1,10 -, 1,4- and 1,5-quinoid tautomeric complexes of boric acid and borate esters differing by the coordination bonds with carbonyl groups existing in the dynamic equilibrium. The deepening of the reagents color in the presence of boron does not a result only of the complexation, but in the accompanying shift of the tautomeric equilibria.

Existing views on the deprotonation and complexation of 1-amino-4-hydroxyanthraquinone are wrong. This compound, its anions, and complexes with metals are not individual substances, but they form a dynamic equilibrium mixture of keto-enol (keto-oxide) and amino-imine tautomers. Different samples of the same compound differ by the tautomeric composition, the respective information is contained in their electron absorption spectra. In weak alkaline solutions the deprotonation occurs exclusively at the hydroxy group. Most typical structure of 1-amino-4-hydroxyanthraquinone anions is 1,10-quinoid, its metal complexes have 9,10-and 1,10-quinoid structures. The ground states of molecules are more responsible for the tautomeric transformations than the excited states. Quantum-chemical calculations of tautomeric anthraquinones by semiempirical PPP methods are more reliable than modern ab initio calculations.

The reactions of the formation of monosubstituted titanium ethylene, diethylene, and triethylene glycolates based on the interaction of glycols with tetrabutoxytitanium in solutions were investigated. It was shown that ethylene glycol predominantly forms cyclic structures: diethylene glycol, a mixture of cyclic and linear structures, and triethylene glycol, mainly linear structures. The comparative analysis of the reaction products showed that the most promising precursor for the synthesis of TiO2 is a titanium compound based on triethylene glycol.

Seven complexes of d elements with rubazinic acid, (4Z)-4-[(5-hydroxy-1,3-dimethyl-1H-pyrazol-4-yl)imino]-2,5-dimethyl-2,4-dihydro-3H-pyrazol-3-one (HRub), were synthesized and studied by IR and UV/Vis spectroscopy and potentiometry. The composition of the complexes in solution was determined by spectrophotometry and their stability constants were calculated. The crystal and molecular structures of [Co(H2O)6](NO3)2 · 2HRub were determined by X-ray diffraction.

The complexes MLCl2 · nH2O and ML2Cl2 · nH2O, where M = Cu(II), Zn and n = 1–4, were isolated and identified due to the reactions of Cu(II) and Zn(II) chlorides with 2,4,7-trinitrofluorene (L1), 2,4,7-trinitrofluorenone (L1a), and 2,4,5,7-tetranitrofluorene (L2). It was shown that, during complex formation, L1 and L2 were oxidized to fluorenones (L1a, L2a) and as neutral ligands formed 1: 1 and 2: 1 complexes with metal cations. A single crystal of tetranitrofluorenone (L2a) was isolated, and its crystal and molecular structure was determined. The complexes were studied by X-ray powder diffraction analysis, their spectral (IR and UV) characteristics were determined, and the structures for the complexes were proposed.

Hydrous zirconia and hafnia xerogels of compositions ZrO2 · 2.5H2O and HfO2 · 2.3H2O are dehydrated in two steps upon heating. First, molecular water is mostly removed from the structures to form phases of compositions ZrO2 · H2O and HfO2 · 0.5H2O. Second, polycondensation of OH groups occurs. Both processes are easier for ZrO2 · 2.5H2O. Apart from these steps, the interaction of water molecules with zirconium-oxygen bridges was found to occur during dehydration of the zirconium compound. The composition of HfO2 · 0.5H2O should actually read as Hf4O7(H2O)(OH)2.

Diversity of electronic absorption spectra of the metal complexes with 1-amino-4-hydroxyan-thraquinone is a consequence of the fact that they exist as equilibrium mixtures of tautomers with the isomeric quinoid structure of the ligand. These complexes are characterized by keto-oxide and amino-imine tautomerism, and samples of the complexes differ by composition of the tautomers.

Six copper(II), iron(III), and chromium(III) complexes with 5,10-dioxo-4,5,9,10-tetrahydro-4,9-diazapyrene derivatives (H2L1-H2L3) have been synthesized and studied by physical methods (IR and electronic absorption spectroscopy, quantum-chemical calculations). The composition of the complexes has been determined and their stability constants in aqueous dimethylformamide solutions have been calculated. The energy characteristics, electronic structure and geometry of isolated diazapyrenes and their tautomeric forms have been calculated by the PM6 method, and their complexes have been modeled.

The disperse dye red 2C regarded as 1-amino-4-hydroxy-9,10-anthraquinone is not a 9,10-anthraquinone derivative. It is characterized by a keto-enol and amino-imine tautomerism, and it consists of equilibrium mixtures of tautomers and conformers containing 4-amino-9-hydroxy-1,10-, 9 amino-4-hydroxy-1,10-, 9 amino-10-hydroxy-1,4-anthraquinones, 9 hydroxy-1,10-anthraquinone 10-imine, and also their conformers with a single intramolecular hydrogen bond. The significant differences in the absorption spectra known for this dye originate from the dissimilar isomeric composition of the samples of this dye prepared or purified by various procedures

Reaction of epoxy-diane resin with complex based on monoamide of phosphonic acid and ammonium chloride (MODAF) is studied. It is established that the MODAF equivalent in the reaction with epoxy resin is equal to 1/5 of its molecular weight. Epoxy resin is cured via the reactions of both monoamide and ammonium chloride. The dependence of the epoxide and hydroxyl groups has a stepped character over time, which is probably due to the existence of certain threshold concentrations of the curing coefficients. The investigated reaction is a new example of macroscopic coherence manifestation.

Products of reactions of hydroxyanthraquinones with boric acid exist as equilibrium mixtures of tautomeric boron complexes and boric acid esters in which one or two boron atoms are not coordinated to carbonyl groups. Tautomerism is responsible for the appearance of several πl,π bands in the electronic absorption spectra and considerable differences in the data obtained by different authors. Boron-containing quinizarin derivatives have mostly 1,10-quinoid structures. The use of quinizarin as an analytical reagent for the determination of boron is based on replacement of tautomeric equilibria due to complex formation rather than on coordination-induced red shift of the absorption maximum.

The molecular and crystal structure of bis(4-aza-9-fuorenone)dibromocopper(II) [CuL 2Br2] was determined by X-ray diffraction. The organic molecule is coordinated in the monodentate fashion with participation of lone electron pairs of heterocyclic nitrogen atoms of 4-aza-9-f1uorenone. The coordination unit parameters were calculated by DFT with PBE functional. The Cu-Br and Cu-N coordination bonds are covalent, the electron pairs of the ligand are transferred to the vacant orbitals of the central ion. The computational methods adequately reproduce the structure of the IR spectrum of the complex.

The complexes of general formula MCl2∙L1-4∙nH2O (where L1 - N-(2,4,7-trinitrofluorenilidene-9)-p-dimethyl-aminoanilin, L2 - N-(2,4,5,7-tetranitrofluorenilidene-9)-p-dimethylaminoaniline, L3 - N-(2,4,7-trinitrofluorenilidene)-N-(p-dimethylaminophenyl)hydroxylamine, L4 - N-(2,4,5,7-tetranitrofluorenilidene-9)-N-(p-dimethylaminophenyl)-hydroxylamine; M=Cu, Co, Ni, Zn; n= 1-3 have been synthesized and investigated by different methods. Spectral criteria of co-ordination of the molecules L1 –L4 in electronic adsorption spectra were detected.

Fine structure of πl,π* absorption of mono- and dications derived from 1,5- and 1,8-dihydroxyanthraquinones originates from their existence as dynamic equilibrium mixtures of isomers differing by position of the positive charge, double bond distribution, and number of intramolecular hydrogen bonds. Protonation is accompanied by displacement of isomeric equilibria. Isomeric transformations of protonated dihydroxyanthraquinones involve mainly excited states of their molecules.

Different mechanisms of the catalytic action of tetrabutoxytitanium in esterification and transesterification reactions are analyzed. New evidence is obtained in favor of the nonionic mechanism of ester formation catalysis by glycol-tetrabutoxytitanium adducts in esterification reactions.

The oxidative nitration of 2-amino-3-hydroxypyridine in the presence of rare-earth metal cations allocates 2-ethoxy-3-hydroxy-4,6-dinitropyridine (I) as one of the reaction products. Treating compound I with a sodium hydroxide solution gives diaquasodium bis(2-ethoxy-3-hydroxy-4,6-dinitropyridinate) (II). The molecular and crystal structures of I and II were studied. The compounds were characterized by spectroscopic methods (IR and electronic absorption spectroscopy). The acidic dissociation constant of compound I was evaluated.

The crystal and molecular structures of bis(2-methylimidazolium) tetrabromocuprate(II) are determined. The linear dependences of the degree of distortion of the CuBr 4 2− coordination polyhedron on the protonation constant of the organic cation are revealed for the structures with θ < 140°. The dependence of the hydrogen bond parameters (distances H…Br and N…Br, angle NHBr) on the degree of distortion of CuBr 4 2− is shown. The degree of distortion of CuX 4 2− (X = Cl, Br) is determined by the type of the organic cation and is almost the same for the CuBr 4 2− and CuCl 4 2− polyhedra. The empirical equations relating the degree of distortion of CuX 4 2− (X = Cl, Br) and the position of the Cu ← X ligand-to-metal charge-transfer band (νLMCT) are obtained.

The compound widely known as 1,4-diamino-9,10-anthraquinone is in fact an equilibrium mixture of 4,9-diamino-1,10-anthraquinone and tautomeric imino forms, 10-amino-9-hydroxy-1,4-anthraquinone 1-imine and its conformer, and 4-amino-1-hydroxy-9,10-anthraquinone 9-imine or 4,9-dihydroxy-1,10-anthraquinone diimine. Amino-imino tautomerism and rotational isomerism are responsible for fine structure of the πl,π*-absorption of the title compound.

Three complexes containing hexachlorodicuprate(II) anions and protonated 4-azafluorenone derivatives as counterions were isolated. The crystal and molecular structures of 4-azafluoren-9-one, (HL1)2[{CuCl2(H2O)}2(μ-Cl)2] · 2H2O (L1), and spectral characteristics of the complexes were determined. Relationships relating the degree of distortion of the crystal structure of the hexachlorodicuprate(II) anions to the spectral characteristics of the compounds were proposed on the basis of the experimental and published data.

Fine structure of quinizarine π l ,π*-absorption in sulfuric acid is defined by isomerism of its protonated products. The monocation is an isomeric mixture, the isomers differ by the charge localization on various carbon atom: 1,4,9-trihydroxy-10-oxo-10H-anthracen-1-onium, 1,9,10-trihydroxy-4-oxo-4H-anthracen-1-onium, and 4,9,10-trihydroxy-10-oxo-10H-anthracen-1-onium. For the dication the structures found were exclusively the conformers of 1,4,9,10-tetrahydroxyanthrqacene 1,10-dication containing 0 to 2 intramolecular hydrogen bonds. The protonation leads to a shift of the tautomeric and conformational equilibria characteristic of quinizarine.

The (HL n )2[CuCl4] complexes (where L n are organic nitrogen-containing bases with n = 1–6) were synthesized. The crystal and molecular structures of bis(2-methylimidazolium) tetrachlorocuprate(II), (HL1)2[CuCl4], were determined. The spectral characteristics of the complexes were measured. The correlations between the degree of distortion of the crystal structure of the tetrachlorocuprate anion and the hydrogen bond parameters and the spectral characteristics of compounds were obtained.

The complexes M(L1, 2)2 · nH2O, where M = Co(II), Ni(II), Cu(II), and Zn; n = 2 and 3, were synthesized by the reaction of Co(II), Ni(II), Cu(II), and Zn(II) chlorides with 2,4,7-trinitro-9-fluorenone oxime (HL1) and 2,4,5,7-tetranitro-9-fluorenone oxime (HL2) and identified. It was shown that HL1, 2 were coordinated by metal cations in the anionic form in a 2: 1 ratio. A single crystal of the solvate of HL2 with acetonitrile (1: 1) HL2 · NCCH3 was isolated, and its crystal structure was determined. The spectral characteristics were determined, and the acidity constant of HL1 was calculated. The structures for the synthesized complexes were proposed.

The reactions of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Cd with 2,3-dihydroxyquinoline (H2L) were used to synthesize and identify the complexes M(HL)2 · 2H2O (M = Mn, Ni, Cu), Fe(HL)OH · 2H2O, Co(HL)OH · H2O, Cd(H2L)Cl2, where H2L participates in the coordination in the monoanionic or neutral forms with the formation of the chelate cycles. Single crystal was isolated and the crystal structure of H2L was determined. The spectral characteristics of a neutral and anionic form of the ligand were measured, and its complexation with MCl2 was studied in the ethanol solutions. The acidity constant of H2L and the formation constants of the complexes in solutions were calculated.

Seven complexes of manganese(II), copper(II), cadmium, silver(I), samarium(III), and praseodymium( III) with 3-hydroxy-4,6-dinitro-2-ethoxypyridine (HL) were isolated in the crystalline state and studied by IR and UV spectroscopy. The molecular and crystal structures of di(3-hydroxy-4,6-dinitro-2-ethoxypyridinato) diaquacopper(II) [CuL2(H2O)2] were determined. The coordination mode of the organic ligand L− is bidentate chelating through the O(2) oxygen atoms of the hydroxy group and the O(1) atom of the ethoxy group. The coordination polyhedron of the copper atom is a prolate tetragonal bipyramid (4 + 2) with two O(1) atoms in the axial positions (Cu-O(1) 2.413 A) and two O(2) atoms of the two L−ligands and the O(7) atoms of the water molecules in the equatorial plane (Cu-O(2), 1.912 A; Cu-O(7), 1.972 A).

Infrared and electronic spectroscopy and X-ray fluorescent analysis were used to study the structures of 5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazolin-6-one and its 5-ethyl and carboxy and sulfo derivatives. The latter compounds we obtained for the first time. The ketone and its monocarboxy derivative exist as lactam tautomers, and the sulfo derivative, in the zwitter ion form. Electronic and energy characteristics of the compounds were calculated by the Pariser-Parr-Pople method.

Crystal and molecular structure and spectral characteristics are determined for bis(1-amino-4-azafluoren-9-olium) and bis(2-amino-3-hydroxypyridinium) tetrachlorocobaltates(II): CoCl4(C12H11N2O)2 and CoCl4(C5H7N2O)2, respectively. The structural units of the complexes are CoCl42− anions and organic cations protonated at the pyridine nitrogen atom.

1,2,3-Trihydroxy-9,10-anthraquinone (anthragallol) exists as an equilibrium mixture of the 9,10-, 2,9-, 1,2-, and 2,3-quinoid tautomers. Its anion was detected in the 9,10-, 1,10-, 2,9-, and 2,3-quinoid forms, and its metal complexes, the 9,10-and 2,9-quinoid forms. Ionization and complexation of anthragallol can shift the tautomeric equilibrium.

The diversity of the absorption spectra of complexes with carminic acid was shown to be due to the shift of tautomeric equilibria that takes place upon the change in the medium pH, the nature of the metal, and the composition of the complex. A classification of known carminic acid complexes based on the results of correlation analysis of the positions of experimental πl,π* absorption bands with those calculated by PPP quantum chemical methods is proposed.

Tautomerism of β-mono-, β,β′-dihydroxyanthraquinones, and their anions was studied for the first time by quantum-chemical and correlation methods. 2-Hydroxyanthraquinone exists exclusively in 9,10-quinoid form, and its ionization involves a tautomeric transformation into 10-oxido-2,9-anthraquinone. β,β′-Dihydroxyanthraquinones can exist as the corresponding 9,10-, 2,9-, 2,6-, and 2,3-quinoid tautomers, and the most characteristic forms of their anions are 2,9-quinoid structures. The considerable difference in the known spectra of the same compound is due to the shifts of the tautomeric equilibria.

Carminic acid exists as an equilibrium mixture of 9,10-, 1,4-, 1,10-, 2,9-, and 1,7-anthraquinoid tautomers. Its anions have 9,10-, 1,4-, 1,10-, and 2,9-anthraquinoid structures. No conformational equilibria were detected for carminic acid anions. Variation of the solvent and pH and ionization are accompanied by displacements of tautomeric equilibria. Shifts of the long-wave absorption maxima due to tautomeric transformations are determined mainly by change in the energy of the ground rather than excited states of molecules.

The formation of complexes with quinalizarin was found to occur through the peri-hydroxycarbonyl groups with participation of tautomers and conformers. The diversity of the electronic absorption spectra of quinalizarin complexes is explained not only by the ligand ionization degree but also by the shifts in the tautomeric and conformer equilibria. The classification of the known quinalizarin complexes is suggested on the basis of spectrophotometric data and quantum-chemical calculations of the π l ,π*-band position by the Pariser-Parr-Pople method.

Quinalizarin and anions derived therefrom exist as equilibrium mixtures of different tautomers and conformers, whose structure depends on the conditions. Quinalizarin was shown to have 9,10-, 1,10-, 1,4-, 1,5-, 1,7-, and 2,9-quinoid structures, but not 1,2-quinoid structure; and its anions in ethanol media were identified as 9,10-, 1,10-, 2,9-, and 1,5-quinoid tautomers. Interactions with solvents and ionization could give rise to displacement of tautomeric and conformational equilibria, leading to considerable change in the number and position of π l ,π* bands in the electronic absorption spectra, which are responsible for the color.

1,4,5-Trihydroxy-9,10-anthraquinone and its substituted derivatives exist in equilibrium of structures distinguished by quinoid tautomerism and rotational isomerism. Their electron absorption spectra contain π1, π*-bands corresponding to 9,10-and 1,10-, more seldom to 1,5-and 1,4-anthraquinoid structures. Of three isomeric 1,10-anthraquinones only 4,8,9-trihydroxy-1,10-antraquinones were found. All tautomer may exist as conformers with contiguous CO and OH groups not bound by an intramolecular hydrogen bond. The considerable difference in color of structurally similar substituted compounds is due to tautomerism and conformer transformations.