Irina V. Omelchenko

Ionization and tautomerism of methyl fluorescein and related dyes

The protolytic equilibrium of methyl ether of fluorescein is studied in water, aqueous ethanol, and in other solvents. The constants of the two-step dissociation are determined by spectrophotometry. In water, the fractions of the zwitterionic, quinonoid, and lactonic tautomes are correspondingly 11%, 6%, and 83%, as deduced from the UV-visible spectra. Corresponding study of the ionization of the methyl ether ester of fluorescein, fluorescein ethyl ester, and sulfonefluorescein allows testing the correction of the attribution of the microscopic dissociation constants of methoxy fluorescein. The results of nuclear magnetic resonance and infrared spectroscopy, as well as the X-ray analysis confirm the predomination of the lactonic structure of the molecular species in solid state and in DMSO. Contrary to it, the spectroscopic studies in both hydrogen-donor bond (HDB) and non-HBD solvents confirm that the presence of lactonic monoanion is atypical for the dye under study and, with high probability, also for the mother compound fluorescein.

Substituent effects and aromaticity of six-membered heterocycles

Structure, aromaticity, relative stability, and conformational flexibility of nitro and amino substituted monoheterocyclic analogous of benzene were studied by ab initio quantum-chemical method at MP2/aug-cc-pvDZ level of theory. Amino derivatives were found to be slightly less aromatic than nitro derivatives. Strong push–pull interactions were found in α- and γ-aminochalcogenopyrylium cations and, in less extent, in α- and γ-aminopyrydines. These molecules are less aromatic but more stable, as compare to their β-isomers. All heterocycles with 3rd and 4th row heteroatoms reveal C–NO2 bond elongation accompanied by C–Heteroatom bond shortening in β-nitro isomers, and strong inequality of two endocyclic C–Heteroatom bonds in α-amino isomers.

Tris(2,2′-bipyridine-κ2N,N′)cobalt(III) tris­(oxalato-κ2O1,O2)ferrate(III) mono­hydrate

The title compound, [Co(C10H8N2)3][Fe(C2O4)3]·H2O, consists of two discrete tris(chelate) metal ions (CoIIIN6 and FeIIIO6 chromophores) and a water molecule. The structure is highly symmetrical; the CoIII and FeIII ions occupy positions with site symmetry 3.2. The coordination polyhedra of the metal atoms have a nearly octahedral geometry with noticeable trigonal distortions. The Co—N and Fe—O bond lengths are equal by symmetry, viz. 1.981 (2) and 1.998 (4) Å, respectively. The cations and anions are arranged alternately along their threefold rotation axes parallel to [001], forming chains that are packed in a hexagonal manner. The water molecules occupy voids between the chains. The crystal under investigation was an inversion twin.

Three-component synthesis of tetrasubstituted pyrroles by condensation with amines and arylglyoxals

A one-pot three-component condensation for the synthesis of functionalized pyrroles from arylglyoxal hydrates, acetylacetone or acetoacetic ester, and halo-substituted anilines has been developed. The reaction of ethyl 3-aminocrotonate and arylglyoxal led to the respective ethyl 5-aryl-4-hydroxy-2-methyl-(1H)-pyrrole-3-carboxylates.

Crystal structure of N-hy­droxy­picolinamide monohydrate

In C6H6N2O2·H2O, the N-hydroxypicolinamide molecule adopts a strongly flattened conformation. O—H⋯O interactions and π–π stacking interactions between the pyridine rings organize the crystal components into columns extending along the b axis while N—H⋯N hydrogen bonds link these columns into a two-dimensional framework parallel to (100).

exo-2,3-Epoxybicyclo[2.2.1]heptan-endo-5,6-dicarboximides: versatile starting materials for the preparation of oxazaheterocyclic cage compounds

A convenient method is reported for the synthesis of N-substituted exo-2-hydroxy-6-aza-4-oxatetracyclo[5.2.1.13,508,9]undecan-7-ones, exo-2-hydroxy-6-aza-4-oxatetracyclo[5.2.1.13,508,9]undecanes, and endo-8,exo-9-dihydroxy-4-azatricyclo[5.2.1.02,6]decanes in high to moderate yields. The method involves treatment of easily available exo-2,3-epoxybicyclo[2.2.1]heptan-endo-5,6-dicarboximides with LiAlH4.Graphical abstract

Entropy versus aromaticity in the conformational dynamics of aromatic rings

AbstractComparison of the results of Car-Parrinello molecular dynamics simulations of isolated benzene, pyrimidine and 1,2,4-triazine molecules reveals that the unusually low population of planar geometry of the benzene ring is caused by entropy effects despite its high aromaticity. The decrease in symmetry of the molecule results in smaller changes in entropy and Gibbs free energy due to out-of-plane deformations of the ring, leading to an increase in the population of planar geometry of the ring. This leads to differences in the topology of potential energy and Gibbs free energy surfaces. FigureEntropy vs aromaticity in conformational dynamics of aromatic rings

catena-Poly[[manganese(III)-bis­{μ-2-[(2-hy­droxy­eth­yl)imino­meth­yl]-6-meth­oxy­phenolato-κ3O1,N:O2;κ3O2:N,O1}] iodide]

In the title one-dimensional coordination polymer, {[Mn(C10H12NO3)2]I}n, the potentially tetradentate (O,O,O,N) 2-[(2-hydroxyethyl)iminomethyl]-6-methoxyphenol (H2 L) ligands are mono-deprotonated (as HL −) and coordinated by the metal ions in a tridentate chelate-bridging fashion [2.0111112]. The MnIII atom possesses a distorted trans-MnO4N2 octahedral coordination environment. The bridging ligands lead to [010]-chain polymeric cations {[Mn(HL)2]+}n in the crystal. The charge-balancing iodide ions are disordered over two sites in a 0.690 (2):0.310 (2) ratio and a weak O—H⋯I hydrogen bond occurs. The crystal studied was found to be a racemic twin.

Bis(2-hy­droxy­imino­methyl-6-meth­oxy­phenolato-κ2N,O1)copper(II)

In the title compound, [Cu(C8H8NO3)2], the nearly planar molecule (r.m.s. deviation = 0.037 Å) is centrosymmetric with the CuII atom lying on an inversion center. The CuII atom is tetracoordinated, displaying a slightly distorted square-planar geometry. The main deviation from the ideal geometry is seen in the differences in the Cu—O [1.8833 (10) Å] and Cu—N [1.9405 (13) Å] bond lengths, while angular deviations are less than 3°. Intramolecular O—H⋯O and intermolecular Csp2—H⋯O hydrogen bonds form S(5) and R 2 2(8) ring motifs, respectively. The latter interaction results in chains of molecules along [100].

Aromaticity and conformational flexibility of five-membered monoheterocycles: pyrrole-like and thiophene-like structures

Aromaticity and conformational flexibility of the series of five-membered monoheterocycles with group 14–16 heteroatoms, having one or two lone pairs, were studied with ab initio methods using NICS, ASE and I5 indices. For non-planar molecules like phosphole, aromaticity of their planar transition states was also studied, and a special modification of ASE index was proposed to that end. It was found that the presence of two lone pairs is generally preferable for aromaticity of all heterocycles except CPD and silolyl dianions. Heterocycles with group 16 heteroatoms have consistently lower aromaticity compared to other groups. A lot of structures should be classified as moderate aromatic and non-aromatic. Energies of out-of-plane deformation do not correlate with other indices studied, but reveal the same qualitative trends. Generally, aromaticity of five-membered monoheterocycles depends strongly on both heteroatom type and number of lone pairs on it.