Fragment-molecule adduct ion formation in the mass spectra of cyclic N-acetylamines and related nitramines

Mass spectra of seven related N-heterocyclics, introduced by direct exposure probe, were determined in electron impact (EI) and positive- and negative-ion chemical ionization (PCI and NCI) modes. Proton adducts were the predominant molecular ion species in the EI and PCI modes. In addition, a variety of fragment–molecule adduct ions were observed for each compound in one or more of the modes. The propensity of 1,3,5-trinitrohexahydro-1,3,5-triazine for fragment–molecule adduct formation was high in all three ionization modes. Fragmentation processes were documented by collision-induced dissociation experiments.     

Dispersion interactions and solvent-shift effects

The problem of relating solvent-shift effects to excited-state polarizabilities is discussed. It is found that the chief difficulty is that of estimating the dispersion term in the interaction energy between a solvent molecule and a solute molecule, and it is shown that the differences in the values of excited-state polarizabilities which have been deduced from solvent-shift data are due to widely differing estimates of this dispersion term. In order to obtain meaningful results it is found necessary to assume that the change in the dispersion term is related to the change in the polarizability of a solute molecule on excitation. On the basis of this assumption, the use of a semi-empirical formula which connects solvent-shifts with these changes in the polarizability is discussed and it is found that the accuracy is such that very little useful information can be obtained.

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Zusammenfassung Das Problem, Lösungsmittelverschiebungen mit der Polarisierbarkeit angeregter Zustände in Verbindung zu bringen, wird diskutiert. Dabei zeigt sich, daß die Hauptschwierigkeit im Abschätzen des Dispersionsterms der Wechselwirkung Solvent-Solut-Molekül liegt und daß die Unterschiede in den Polarisierbarkeiten, die sich aus Daten für Lösungsmittelverschiebungen ergeben, auf die sehr unterschiedliche Abschätzung dieses Dispersionsterms zurückgehen. Um sinnvolle Resultate zu erhalten, muß angenommen werden, daß die Änderung des Dispersionsterms mit der Änderung der Polarisierbarkeit eines angeregten Solutmoleküls zusammenhängt. Auf dieser Grundlage wird eine entsprechende semiempirische Formel diskutiert; jedoch deren mangelnde Genauigkeit läßt keine eindeutigen Aussagen mehr zu.

     

Rate coefficient for the reaction OH + HO2 = H2O + O2 at 1 atmosphere pressure and 308 K

The rate coefficient for the reaction OH + HO₂ =H₂O + O₂ has been determined from measurements of the steady-state absorption of HO₂ at 210 nm, in low-frequency square-wave modulated photolysis of O₃ + H₂O mixtures. The value obtained was (9.9 ± 2.5) × 10^?11 cm³ molecule^?1 s^?1 at 308 K and 1 atm pressure.     

The densities and molar volumes of molten lead(II) dodecanoate/dodecanoic acid mixtures over their complete composition range: Evidence for non-ideal behaviour

Data are presented for the densities and molar volumes of the molten system lead(II) dodecanoate/dodecanoic acid over its complete composition range. For equimolar mixtures, plots of molar volume against temperature show curvature at high temperatures, suggesting deviations from ideal behaviour. Support for this comes from a plot of molar volume at constant temperature against acid mole fraction. Densities and molar volumes are reported for lead (II) carboxylate/carboxylic acid (0.5 mole fraction) and for pure carboxylic acid for the even chain acids C₁₀ to C₁₈. The molar volumes at constant temperature in these cases are linear functions of chain length, although the volume occupied per methylene group in equimolar mixtures is suggested to be slightly smaller than with pure soap or pure acid. An explanation for non-ideal behaviour becoming more marked at higher temperature is given in terms of acid monomer-dimer equilibria.     

Perturbation theory for excited states of molecules

Components of the electric polarizability tensor are calculated for the three lowest singlet and three lowest triplet excited states of a number of conjugated molecules. The method used is the configuration interaction perturbation theory described in the first two papers of this series. A simpler method based on Hückel theory is examined and found to be unsatisfactory.     

Interaction between the water soluble poly{1,4-phenylene-[9,9-bis(4-phenoxy butylsulfonate)]fluorene-2,7-diyl} copolymer and ionic surfactants followed by spectroscopic and conductivity measurements

The interaction has been studied in aqueous solutions between a negatively charged conjugated polyelectrolyte poly{1,4-phenylene-[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer (PBS-PFP) and several cationic tetraalkylammonium surfactants with different structures (alkyl chain length, counterion, or double alkyl chain), with tetramethylammonium cations and with the anionic surfactant sodium dodecyl sulfate (SDS) by electronic absorption and emission spectroscopy and by conductivity measurements. The results are compared with those previously obtained on the interaction of the same polymer with the nonionic surfactant C12E5. The nature of the electrostatic or hydrophobic polymer-surfactant interactions leads to very different behavior. The polymer induces the aggregation with the cationic surfactants at concentrations well below the critical micelle concentration, while this is inhibited with the anionic SDS, as demonstrated from conductivity measurements. The interaction with cationic surfactants only shows a small dependence on alkyl chain length or counterion and is suggested to be dominated by electrostatic interactions. In contrast to previous studies with the nonionic C12E5, both the cationic and the anionic surfactants quench the PBS-PFP emission intensity, leading also to a decrease in the polymer emission lifetime. However, the interaction with these cationic surfactants leads to the appearance of a new emission band (approximately 525 nm), which may be due to energy hopping to defect sites due to the increase of PBS-PFP interchain interaction favored by charge neutralization of the anionic polymer by cationic surfactant and by hydrophobic interactions involving the surfactant alkyl chains, since the same green band is not observed by adding either tetramethylammonium hydroxide or chloride. This effect suggests that the cationic surfactants are changing the nature of PBS-PFP aggregates. The nature of the polymer and surfactant interactions can, thus, be used to control the spectroscopic and conductivity properties of the polymer, which may have implications in its applications.     

Electrical conductance,density, and viscosity of the molten system lead(II) dodecanoate/lead(II) oxide

Data are presented for densities, electrical conductances, and viscosities of the molten system lead(II) dodecanoate/lead(II) oxide concentrations up to 0.22 mole fraction of the oxide. Values of ?₀ obtained from extrapolation of graphs of density againts temperature are seen to decrease on adding small quantities of PbO, but to increase on adding further PbO. Results from thermal analysis suggest that this may be due to a change in structure of the liquid phase from small. spherical to long, cylindrical micelles. Over the concentration range studied, molar volumes are linear functions of concentration at any particular temperature. The molar volumes of the system lead(II) carboxylate/lead(II) oxide for the even chain acids C₁₀ to C₁₈ are linear functions of chain length. Arrhenius plots for the electrical conductance of the mixtures show curvature, as in other lead(II) dodecanoate systems. The activation energies for conductance in the low temperature region show a steady decrease with increasing PbO concentration and it is proposed that this arises from increased mobility of the charge carrier. The specific conductance at any temperature decreases with increasing mole fraction of oxide, indicating the oxide to be essentially undissociated in the melt. The activation energy for viscosity shows a dramatic increase on adding small amounts of PbO. This is suggested to arise from a change in the structure of the melt. Studies of the viscosities of the system lead(II) carboxylate/lead oxide as a function of chain length for the even chain acids C₁₀ to C₁₈ suggest a slight decrease in the size of the unit of viscous flow when oxide is present.     

Formation of 13C-, 15N-, and 18O-labeled guanidinohydantoin from guanosine oxidation with singlet oxygen. Implications for structure and mechanism

Guanosine labeled with 15N at N1, amino, and N7 and 13C at either C2 or C8 was oxidized by Rose Bengal photosensitization (singlet oxygen) in buffered aqueous solution. At pH > 7, spiroiminodihydantoin was the major product, while at pH < 7, guanidinohydantoin (Gh) was the principal product. 15N and 13C NMR studies confirmed that Gh was formed as a mixture of slowly equilibrating diastereomers. Experiments conducted in H218O indicated that Gh and Sp each contained one oxygen atom derived from O2 and one from H2O. Tandem mass spectrometry was used to identify the C4 carbonyl of Gh as the one labeled with 18O, supporting a mechanism involving attack of water at C5 of a dehydro-8-oxoguanosine intermediate.