Conventional fluorescence spectrometry of polynuclear aromatic hydrocarbons in Shpol'skii matrices at 77 K

A simple fluorimeter assembled from commercial components and its use for the study and application of the Shpol'skii effect on polynuclear aromatic hydrocarbons (PAHs) in n-alkane matrices at 77 K are described. The correlation between the dimensions and geometries of PAHs and their corresponding Shpol'skii solvents is considered. Analytical figures of merit have been evaluated, and the power of the Shpol'skii technique with a conventional fluorimeter in the direct qualitative and quantitative determination of 11 PAHs in mixture is demonstrated. Comparisons with conventional room-temperature fluorescence and laser-excited Shpol'skii spectrometry are also commented upon.     

Solubility of benzilic acid in select organic solvents at 298.15 K

Experimental solubilities are reported for benzilic acid dissolved in ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 2-propanol, 2-butanol, 2-methyl-1-propanol, diethyl ether and methyl tert-butyl ether at 298.15?K. Results of these measurements reveal that the observed solubilities in the nine alcohol solvents fall within a fairly narrow mole fraction range of each other. Benzilic acid is also very soluble in the two ether solvents studied.     

Cyclization and decomposition of nitroguanylazide in organic solvents

When nitroguanylazide is heated in solution, it may cyclize to form a mixture of 5-nitroaminotetrazole and the diammonium salt of 5-nitroaminotetrazole or it may decompose, depending on the nature of the organic solvent.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, 945–946, July, 1987.     

Enthalpy of mixing of methacrylic acid with organic solvents at 293 K

The enthalpies of mixing of binary systems of methacrylic acid with acetonitrile, benzene, hexane, 1,2-dichloroethane, and acetic acid are measured calorimetrically at 293 K and atmospheric pressure. The enthalpy of mixing of all the studied binary systems is positive over the range of concentrations.     

Quasi-linear fluorescence and phosphorescence of some aromatic and heterocyclic compounds in tetrahydrofuran at 77 K

The fluorescence and phosphorescence emission spectra of 31 polynuclear aromatic hydrocarbons and a number of heterocyclic compounds have been studied in tetrahydrofuran and in n-paraffin solvents at 77 K. A comparison of the characteristics of the quasi-linear luminescence emission observed in these solvents has been made. The effect of the presence of peroxide impurities in the tetrahydrofuran solvent on the emission spectrum observed for coronene has been investigated.     

Thermochemistry of dissolution,solvation, and hydrogen bonding of anilines in proton-acceptor organic solvents at 298.15 K

Enthalpies of dissolution at infinite dilution (298.15 K) of aniline, N-methylaniline, and N,N-dimethylaniline in a series of proton-acceptor solvents of different classes of compounds have been measured. The solvation enthalpies have been determined, and its relationship with the anilines structure has been analyzed. Enthalpy of hydrogen bonding in the complexes of aniline (1: 2) and N-methylaniline (1: 1) with the solvents has been calculated. In the case of aniline complexes, negative cooperativity of hydrogen bonding has been revealed, the effect enhancing with increasing the solvent proton-acceptor ability.     

Photophysical properties of some phenetidines in non-polar and hydrogen bonding solvents at room temperature and 77 K

The present study was undertaken to investigate the photophysical processes in o-, m- and p-phenetidines, when dissolved in nonpolar and hydrogen bonding solvents, in their ground state and excited electronic state S₁, both at 300 and 77 K. In the ground as well as in the S₁ state it is proposed that the o-phenetidine molecule possesses a structure in which NH₂ and OC₂H₅ groups are away from each other, both in nonpolar cyclohexane (CH) and H-bond acceptor solvent triethylamine (TEA). The formation of a transient or nonemissive charge transfer (CT) complex resulting from strong excited state hydrogen bonding interaction with TEA is found to be responsible for the observed fluorescence quenching of the proton donor phenetidines at 300 K. From the room as well as low (77 K) temperature electronic absorption and steady state fluorescence studies, it was deduced that nonplanarity in the structure of the molecules increases as one moves from aniline to the phenetidines. It is suggested that in the solvent stiffening temperature 77 K, triplet states of all the phenetidines (o-, m- and p-) acquire some nπ* character due to conformational changes, whereas ππ* character is retained in their S₁ state. This facilitates a larger intersystem crossing (ISC) rate in phenetidines relative to the situation in aniline where both S₁ and T₁ possess the same nπ* nature at 77 K due to its more planar structure. However, ISC efficiency in phenetidines at 77 K is found to be impeded, especially in the case of o- and m-isomers, in the presence of TEA as inferred from the lowering of φ_p/φ_⨍ values and the increment of τ_p. In p-phenetidine, rapid equilibrium between a triplet state hydrogen bonded species and free molecules during the triplet excited state lifetime is suggested.     

Cocondensation reactions of heterocyclic aromatic compounds with lithium, calcium and magnesium atoms at 77 K

Calcium and magnesium atoms were cocondensed with aromatic heterocycles containing five- and six-membered rings in the presence of THF at 77 K. In the case of calcium the cocondensation with five-membered heterocyclic compounds resulted in C-H bond activations and led to the corresponding aryl calcium compounds, while magnesium did not show comparable reactions. When six-membered heterocyclic compounds, e.g., pyridine and 4-methylpyridine (4-picoline) were cocondensed with calcium, magnesium and lithium atoms, all reactions led to the formation of non-metallated aromatic products and the formation of metal hydride. DFT calculations at the B3LYP/6-31G** level of theory were carried out in order to interpret the pathways of the cocondensation reactions using calcium atoms and identify the possible intermediates involved. In all reactions π- and σ-complexes between calcium atoms and the heterocyclic aromatic reactant were found as stable intermediates on the energy hypersurface.     

Solubility and dissolution thermodynamics of tetranitroglycoluril in organic solvents at 295–318 K

The solubility data of tetranitroglycoluril in acetone, methanol, ethanol, ethyl acetate, nitromethane and chloroform at temperatures ranging from 295–318 K were measured by gravimetric method. The solubility data of tetranitroglycoluril were fitted with Apelblat semiempirical equation. The dissolution enthalpy, entropy and Gibbs energy of tetranitroglycoluril were calculated using the Van’t Hoff and Gibbs equations. The results showed that the Apelblat semiempirical equation was significantly correlated with solubility data. The dissolving process was endothermic, entropy-driven, and nonspontaneous.     

Excitation wavelength and solvent dependent emission spectra in weakly polar aprotic solvents at room temperature and 77 K

Excitation wavelength-dependent emission spectra of 4-methyl-2,6-diformylphenol (MFOH) and o-hydroxybenzaldehyde (OHBA) have been examined both in pure weakly polar aprotic solvents and in the presence of a base at room temperature and 77 K. It is shown that fluorescence quantum yield shape, position of the spectra, and number of conformers are dependent upon the excitation energy and also on the proton-accepting ability of the solvents. Fluorescence spectra cannot be correlated with the solvent dielectric properties. At 77 K, deactivation occurs via phosphorescence only at a particular experimental condition in all the solvents studied here. The decay rates are relatively slower in an environment where the probability of hydrogen bonding interaction is stronger.     

Electron scavenging by solutes in ethylene glycol-water glasses at 77 K

The efficiencies of a number of solutes in reducing the concentration of trapped electrons in gamma-irradiated ethyleneglycol-water glasses at 77 K has been studied, inclusive of trap depth variation studies. A model, involving the polarising power of the solutes has been suggested to explain the relative efficiencies of solutes in reducing the yield of trapped electrons.     

Infrared spectrum of hexafluorobenzene crystal at 77 K

Infrared spectra of polycrystalline C₆F₆ are analyzed in the 200 cm⁻¹ to 4000 cm⁻¹ region. The vibrational frequencies agree well with liquid data although many of the bands are split. Mutual exclusion between infrared active and Raman active fundamentals is found.     

Correlation equations for solubility of NaHS in water and organic solvents at 297–323 K

The solubility of NaHS in different solvents had been determined from 297.85 to 342.55 K by an analytical method. A solubility model is proposed and the solubilities calculated by the model show good agreement with experimental data. It provided the basic data for the synthesis of isopropyl mercaptan in industry.     

Photoinduced oxygenation of tryptamines by aromatic amine N-oxides

Irradiation (1) (253-7 nm) of N_a,N_b-dimethyltryptaimne with pyridine N-oxide or benzo[c]cinnoline N-oxide in CH₂Cl₂ yielded 1,8-dimethyl-3a-hydroxy-1,2,3,3a,8-8a,- hexahydropyrrolo[2,3-b]indole (19), while with visible light N_b-(4-cyanobutadienyl)-N_a,N_b,- dimethyltryptamine (21) was obtained. This method was applied to trimethyltryptamine and the corresponding oxindole (34) and the N-formyl derivative (20) were obtained.     

X-ray- and U.V.-induced excitation of adenine, thymine and the related nucleosides and nucleotides in solution at 77 degrees K

Abstract— The light emitted by adenine and thymine and the related nucleosides and nucleotides in ethylene glycol/water glass during irradiation at 77°K with X-rays and 270 nm U.V. light has been studied. It was found that the same radiative levels were excited by both types of radiation. However, the phosphorescence to fluorescence ratios observed with X-rays were considerably enhanced relative to those obtained with U.V. light. This observation was taken to mean that a major fraction of the excitation results from ion recombination, although direct excitation of the triplet manifold as well as intersystem crossing between upper excited levels may have contributed to the enhancement as well. The yields of the X-ray-induced excitation of radiative levels. which were calculated by combining the yields of X-ray-induced emission and the quantum yields observed with u.v.-excitation, corresponded to: G≥ 4.0 excitations per 100 eV of dose absorbed in the solute for adenine and G≥ 1.8 for thymine. The excitation yields obtained for the nucleosides and nucleotides were somewhat smaller than those observed for the corresponding bases. It was inferred from the yields that a substantial fraction of the dose absorbed in the ribose of the nucleosides was transferred to the radiative levels of the constituent bases.