Comparability graphs and molecular properties III. C9 and C10 alkanes

The graph-theoretical approach recently developed for comparing and ordering isomeric chemical compounds is extended and applied to the calculation of various molecular properties of C₉ and C₁₀ alkanes (critical densities, volumes, and pressures; heats and entropies of vaporization; standard entropies in liquid and gas state). The key to the approach is in specifying subsets of comparable isomers which are located in the same paths in the so-called comparability graphs. Optimized samples for structure-property correlations are thus obtained.     

Photochromism of new unsymmetrical isomeric diarylethenes bearing a pyridine group

A new class of unsymmetrical isomeric diarylethenes bearing a terminal pyridine group was synthesized and their structures were determined by single-crystal X-ray diffraction analysis. The effects of the nitrogen atom position in the pyridine group on their properties including photochromism, acidchromism, and fluorescence were investigated systematically. Among the three isomeric derivatives, the cyclization quantum yield and the absorption maxima of the ortho-substituted diarylethene were the biggest, while the fluorescence quantum yield of the para-substituted diarylethene was the biggest. Furthermore, the three isomeric diarylethenes exhibited multi-addressable switching behaviors by the stimulation of acid/base and light. Addition of trifluoroacetic acid to solutions of these diarylethenes produced the protonated derivatives, which also showed excellent photochromic behaviors, but only the para-substituted diarylethene exhibited a notable color change of solution from crimson to violet. The results revealed that the effects of the nitrogen atom position in the terminal pyridine group played a very important role during the process of photoisomerization for these isomeric diarylethene derivatives.     

Comparability graphs and molecular properties: IV. Generalizations and applications

The development of a recently proposed method for calculating molecular properties is outlined. The approach is based on the idea of constructing optimized compound samples for structure—property or structure-activity correlations by means of the so—called comparability graphs (CG) of isomeric compounds. A dynamic comparability principle is devised, proceeding from a series of standard molecular rearrangements described in graph—theoretical terms as rules on molecular branching and cyclicity. An extension of the approach is presented for both the construction of CG's and their combination for variable numbers of atoms. The method is applied to various physico-chemical properties, which are thus divided into three groups according to the degree to which they are conditioned by molecular topology. The Wiener topological index is shown to produce a highly linear correlation with the alkane critical densities and volumes, as well as with their heats and entropies of vaporization.Dedicated to the memory of Professor Oskar E. Polansky, a pioneer of chemical graph theory     

Influence of molecular configuration and conformation on the electromigration of oligosaccharides in narrow bore capillaries

Capillary electrophoresis enables fast, high efficiency separations of oligosaccharides, wherein positional and/or linkage isomers, bearing the same charge-to-mass ratio, can readily be separated based on hydrodynamic radius differences. Fundamental electrophoretic mobility theory was used to investigate the correlation between changes in hydrodynamic volume equivalent radius and corresponding electrophoretic characteristics of oligosaccharides with different molecular properties. Fluorescently derivatized isomeric malto-, cello-, and isomaltooligosaccharide ladders, differing only in their linkage type of α1→4, β1→4, and α1→6, respectively, as well as a sterically larger N-acetylchitooligosaccharide ladder were used as model compounds. Mere differences in glycosidic linkage type or anomericity of isomeric oligo-glucoses had a decisive impact on their electromigration behavior, thus reflecting discrepancies in hydrodynamic radii and associated molecular conformations. The impact of hydrogen bridges, and associated availability of hydroxyl groups, on the molecular conformations, was investigated by hydrophilic interaction liquid chromatography. The experimentally observed electrophoretic and chromatographic differences between isomeric oligo-glucoses strongly suggested that special attention must be given when homooligosaccharide ladders are employed for normalization and comparability purposes, for example, in glucose unit calculation based structural elucidation.     

Independent isomeric yield ratios of 95m,gNb in the natMo(γ, pxn) and natZr(p,xn) reactions

The independent isomeric yield ratios of ^95m,gNb from the ^natMo(γ, pxn) reactions with bremsstrahlung end-point energies of 45, 50, 55, 60, and 70 MeV were determined by an activation and an off-line γ-ray spectrometric technique at the Pohang accelerator laboratory (PAL), Korea. The isomeric yield ratios of ^95m,gNb from the ^natZr(p, xn) reactions were also determined in eight different proton energies within 19.4–44.7 MeV by a stacked-foil activation and an off-line γ-ray spectrometric technique using the MC-50 cyclotron of Korea Institute of Radiological and Medical Sciences (KIRAMS), Korea. The measured isomeric yield ratios of ^95m,gNb from the present work and the literature data in the ^natMo(γ, pxn) and ^natZr(p, xn) reactions were compared with the similar literature data in the ^natMo(p, αxn) reactions. It was found that the isomeric yield ratio of ^95m,gNb increases with projectile energy, which indicate the effect of excitation energy. However, at the same excitation energy, the isomeric yield ratios of ^95m,gNb in the ^natZr(p, xn) and ^natMo(p, αxn) reactions are higher than those in the ^natMo(γ, pxn) reaction, which indicates the role of input angular momentum. The isomeric yield ratios of ^95m,gNb in the ^natMo(γ, pxn), ^natZr(p, xn), and ^natMo(p, αxn) reactions were also calculated using computer code TALYS 1.4. The calculated isomeric yield ratios of ^95m,gNb from three reactions increase with excitation energy. However, in all the three reactions, the calculated values are significantly higher than the experimental data.     

Synthesis, characterization and antimicrobial activity of some new 1-(fluorobenzoyl)-3-(fluorophenyl)thioureas

Synthesis of a variety of new 1-(isomeric fluorobenzoyl)-3-(isomeric fluorophenyl)thioureas (1a-t) was accomplished in two steps. The synthetic route involves the reaction of equimolar quantities of isomeric fluorobenzoyl chlorides with potassium thiocyanate in anhydrous acetone to afford the corresponding isothiocyantes in situ, followed by treatment with equimolar quantities of isomeric fluoroanilines. All of the synthesized compounds (1a-t) were screened for their in vitro antibacterial activity using Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aureginosa). The minimum inhibitory concentration (MIC) was also determined for the most active compounds. In vitro antifungal activity was also determined against the five fungal species (Rhizopus oryzae, Aspergillus tereus, Fusarium oxysporum, Aspergillus niger, Aspergillus fumigatus). In general, the antifungal activity of compounds was better than their antibacterial activity.     

Photochemical reactions of substituted cyclobutadieneiron tricarbonyl complexes with acetylenes

When mixtures of monosubstituted cyclobutadieneiron tricarbonyl complexes and propyne are irradiated, substituted toluenes are obtained. The composition of the isomeric mixture is influenced by the nature of the substituent in the metal complex. Electron-withdrawing groups produce mixtures containing a very large percent of the ortho isomer while electron-releasing groups yield mixtures rich in the para isomer. Complex mixtures of isomeric benzene compounds are obtained when substituted acetylenes are allowed to react with methyl- or isopropylcyclobutadieneiron tricarbonyl.     

Adsorption of nitrobenzene, aniline and nitroanilines on the surface of a basal face of graphite

Thermodynamic characteristics of the adsorption of nitrobenzene, aniline, and isomeric nitro-anilines are determined experimentally and from molecular statistics in the range of the closest packing of a graphite surface according to equilibrium gas adsorption chromatography. It is found that graphitized thermal carbon black is characterized by high selectivity upon the chromatographic separation of isomeric nitro-anilines (retention increases in the series of ortho, meta, and para isomers). Using the atom-atomic approximation of the semi-empirical molecular statistical theory of adsorption, parameters are calculated for the potential function of the pair intermolecular interaction of the NO₂ group in nitrobenzene and the N atom in aniline with the C atoms in a basal face of graphite. The effect of the NH₂ and NO₂ groups on the parameters of adsorption for isomeric nitroanilines as a result of direct polar conjugation is demonstrated and must be assumed when performing molecular statistical calculations.     

Formation of isomeric terphenyls and triphenylene by pyrolysis of benzene

The pyrolysis of benzene has been investigated at 773, 923, and 1073 K and the mechanisms of formation of isomeric terphenyls and triphenylene have been studied, the results being compared with those obtained by pyrolysis of benzene solutions containing diphenyl and o=terphenyl. No differences in the mechanisms of the formation of terphenyls and triphenylene could be observed at the selected temperatures, even if ring fission and a higher degree of polymerization occurred at 1073 K. The addition of diphenyl and o-terphenyl showed that the reactions leading to the formation of isomeric terphenyls and triphenylene in the pyrolysis of pure benzene do not pass through stable intermediates.     

[2+2+2] cycloaddition reactions of α,β-unsaturated N-arylaldimines,acetylenedicarboxylates and 2-arylidene-1,3-indanediones

The domino [2+2+2] cycloaddition reaction of α,β-unsaturated N-arylaldimines, dialkyl acetylenedicarboxylates and 2-arylidene-1,3-indanediones in dry methylene dichloride at room temperature afforded isomeric 2′-styryl-1,2′,3,4′-tetrahydro-1′H-spiro[indene-2,3′-pyridines] in good yields. Under similar conditions, the reaction of α,β-unsaturated N-arylaldimines with two molecules of dialkyl acetylenedicarboxylates resulted in 1-aryl-6-styryl-1,6-dihydropyridine-2,3,4,5-tetracarboxylates. Additionally, the three-component reaction of α,β-unsaturated N-arylaldimines, dimethylacetylenedicarboxylate and benzoyl cyanide also gave isomeric 1,3-oxazine-4,5-dicarboxylates.     

The influence of different evaluation techniques on the results of interlaboratory comparisons

The influence of different evaluation techniques on the results of an interlaboratory comparison for the determination of nutrients in ground- and surface water was investigated. The outlier-test procedure was found to influence the interlaboratory standard deviations (SDs), but not the averages. It was shown that even small differences in the numbers of outliers detected can change the SD severely. Comparing the outlier-test procedures of Hampel, Grubbs and Graf-Henning, it was found that Hampel's test detected the most outliers, thus generally resulting in smaller SDs between interlaboratory comparisons. The Graf-Henning test detected the fewest outliers and its application resulted in the highest SDs of the three test procedures investigated. The comparison of different summarising indices, namely the rescaled sum of z-scores, average of absolute z-scores and average deviation showed no comparability. Possibilities to improve the comparability of interlaboratory comparisons and to minimise misunderstandings are suggested.     

Efficient organic sensitizers containing benzo[cd]indole: Effect of molecular isomerization for photovoltaic properties

Two isomeric organic dyes, JK-51 and JK-52 containing benzo[cd]indole were synthesized. Under standard global AM 1.5 solar condition, the JK-51 sensitized cell gave a short circuit photocurrent density of 17.43 mA/cm², open circuit voltage of 0.680 V, and a fill factor of 0.71, corresponding to an overall conversion efficiency η of 8.42%. On the other hand, a solar-to-electric conversion efficiency of 6.88% was achieved with the isomeric dye JK-52. We found that the power conversion efficiency was shown to be quite sensitive to the isomeric configurations.     

Kinetics of azidation of isomeric benzenedicarbonitriles

Rate constants and activation parameters of two-step azidation of isomeric dicyanobenzenes with dimethylammonium azide in DMF at 70–100°C were determined. Tetrazole rings are formed from cyano groups in dicyanobenzenes in a stepwise mode following the 1,3-dipolar cycloaddition pattern. The rate of azidation of isomeric dicyanobenzenes is considerably higher than the rate of subsequent azidation of intermediate cyanophenyltetrazolides. The azidation rate constant decrease in going from m-dicyanobenzene to its para and ortho isomers.     

Synthesis of new analogues of diphenylpyraline

1-Unsubstituted 4-dimethylamino-5,6-dihydropyridine-2(1H)-thiones were converted to isomeric piperidin-4-ols which were separated and N-methylated to 2-substituted 1-methylpiperidin-4-ols. Their 1-phenyl analogues were prepared from 4-dimethylamino-5,6-dihydro-1-phenylpyridine-2(1H)-thiones. After their conversion to dihydro-1-phenylpyridin-4(1H)-ones the hydrogenation gave isomeric 1-phenylpiperidin-4-ols which were separated. O-Alkylation of the 1-substituted piperidin-4-ols by various methods yielded 2-substituted analogues of diphenylpyraline. Their antimycobacterial activity was examined. The configurations and conformations of the piperidine derivatives were investigated by NMR spectroscopy.     

iso-PsE, a new pseudopterosin

We describe the discovery of a new member of the pseudopterosin class of marine natural products. Its structure is isomeric with that of pseudopterosin E and has therefore been given the name iso-PsE.     

Photochemical synthesis of isomeric (E/Z)-3-alkylidene-3H-isobenzofuranones

The synthesis of isomeric (E/Z)-3-alkylidene-3H-isobenzofuranones by photoisomerization of 2-aroyl-2-methyl/benzylindan-1,3-diones in high yields is described.     

Isomeric yield ratios for the natNd(γ, xn) 139m,g; 141m,gNd reactions in the bremsstrahlung energy region from 45 to 60 MeV

The independent isomeric yield ratios (IR) for the ^139m,gNd and the ^141m,gNd isomeric pairs produced from the ^natNd(γ, xn) reactions were determined by the activation and the off-line γ-ray spectrometric technique at the end-point bremsstrahlung energies of 45, 50, 55, and 60 MeV in the 100 MeV electron Linac of the Pohang accelerator laboratory, Korea. The present IR for the ^141m,gNd isomeric pair were compared with those from the literature measured by the bremsstrahlung and the neutron to examine the role of excitation energy. The obtained IR for the ^139m,gNd and the ^141m,gNd isomeric pairs from ^natNd(γ, xn) reactions were compared with those from the ¹⁴¹Pr(p, x), the ^natCe(³He, x), and the ¹³⁶Ce(α, n) reactions to examine the role of parameters in entrance channel i.e. excitation energy and the effect of the input angular momentum. The present IR of ^139m,gNd and ^141m,gNd were compared with those calculated by using the TALYS 1.4 code as well as those from the literature data of above mentioned reactions.     

Enthalpies of formation of nitrodiazoles

The enthalpies of combustion for 3,4,5-trinitro-1Н-pyrazole, 1-methyl-3,4,5-trinitro-1Н-pyrazole, 3,4,5-trinitro-1Н-pyrazole ammonium salt, and ammonium salts of all isomeric dinitropyrazoles and dinitroimidazoles were measured by bomb calorimetry, and the corresponding enthalpies of formation were calculated. The partial contributions to the enthalpies of formation of structurally related compounds were calculated for trinitropyrazole, trinitropyrazolate anion, and anions of isomeric dinitropyrazole and dinitroimidazoles.     

Photochromic and luminescence properties of isomeric forms of the hydronaphthyl radicals

The optical properties of the hydronaphthyl radicals produced upon radiolysis and photolysis of rigid naphthalene solutions in boric acid at 300 K and alcohol, ether and methylcyclohexane at 77 K were investigated. The ESR, absorption and luminescence spectra of the two different isomeric forms of hydronaphthyl radicals have been observed. The estimated values of the lowest electronic transition in α- and β-hydronaphthyl radicals are, respectively: E_α = 2.42 ± 0.03 eV, E_β = 2.66 ± 0.05 eV. It has been found that a reversible photo-induced interconversion between two hydroradicals takes place as well as a dark conversion from the β- to the α-isomer. Analogous photochromic behaviour of the absorption bands of biphenyl, phenanthrene, chrysene and fluorene rigid solutions have also been identified as reversible interconversion between isomeric hydroradicals.     

The question of anomalies in the friedel-crafts acylation of haloalkylbenzenes : Acetylation of the isomeric bromo-m-xylenes

The fact that Friedel-Crafts acylation in bromoalkylaromatics usually proceeds para to the bromine substituent has been considered to be an anomaly. The acetylation of the isomeric bromo-m-xylenes has been carried out, and product identification has confirmed this type of orientation. However, by a consideration of partial rate factors and competitive reactions, it is shown that these results may be quite acceptable.