E.S.R. spectroscopy of non-cyclic enones

The π-bond model is applied to the calculation of the proton chemical shifts of a range of benzenoid hydrocarbons. The simple calculations give results which compare well with experiment and with calculations based on the ring current model. Least squares fitting of the predicted chemical shifts to the observed values can give an indication of the occurrence of local aromatic groups in larger molecules. This procedure also yields an empirically adjusted estimate of the anisotropy in the molar magnetic susceptibility from the experimental proton chemical shifts. A simple criterion for aromaticity is also given. The overall results suggest that there is no need to associate a special ring current attribute to π conjugation in aromatic molecules.     

Rapid computer simulation of E.S.R. spectra

A fast computer algorithm is presented which permits simulation of the effects of rotational diffusion, electron and nuclear relaxation, microwave power, and modulation frequency upon saturation transfer (passage) E.S.R. spectra. Comparison of theoretical and experimental spectra for nitroxide spin-labelled biomolecules suggests that while the dependence of electron spin-lattice relaxation time upon rotational correlation time is weak, the variation of the ratio of the electron to nuclear spin-lattice relaxation times is significant and consideration of strong nuclear relaxation is necessary for the simulation of spectra characterized by correlation times near the reciprocal of the nitrogen nuclear resonance frequency.     

E.P.R. evidence of sodium clustering in NaxV2O5-β

The β-phase of the vanadium bronzes Na_xV₂O₅ has been studied by E.P.R. as a function of x(0.21 ? x ? 0.33). The behaviour of the spin E.P.R. susceptibility is in agreement with the hypothesis of a complete transfer of electrons from sodium to vanadium sites. In addition, the dependence on sodium concentration indicates that the sodium atoms are not randomly distributed when x < 0.33.     

Photolysis and E. S. R. Studies on Triphenylphosphinecarbethoxymethylene

Although several different groups have studied the photolysis of phosphorus ylides, none have utilized e. s. r. to support the postulated decomposition mechanisms. The fundamental question which awaits a definitive answer is which bond breaks first upon photolysis. Tschesche¹ and de Silva² utilizing the ylides (1) and (2) suggested that the carbon-phosphorus double bond was initially broken while Nagao³ using (3) proposed phenyl-phosphorus bond cleavage.     

CH2Cl和O2的反应动力学

利用时间分辨傅立叶变换红外发射光谱技术研究了CH2Cl+O2的气相基元反应．在实验中首次观测到了振动激发产物CO (v·4)和CO2(o3,v·7)．激发态的CO/CO2 (o3)比率是72.2§7．在QCISD//UB3LYP/6-311++G (d, p)水平上对该化学反应的中间物和产物进行了量子化学计算．其研究结果表明: CH2Cl 自由基首先和O2结合, 生成中间物CH2ClOO， 紧接着发生脱氯反应生成环氧中间物CH2OO，然后再经过一系列的异构化和分解反应，生成最终的产物CO和CO2，和实验观     

The E.S.R. spectrum of irradiated ammonium hypophosphite

Electron spin resonance spectra of irradiated crystals of ammonium hypophosphite (NH₄)⁺(H₂PO₂)^- indicate that the ionic radical H[Pdot]O₂ ^- is initially formed. The hyperfine interaction tensor of the phosphorus nucleus has the principal values 1698, 1228 and 1228 Mc/s. Interaction with the proton gives rise to an almost isotropic hyperfine coupling of 230 Mc/s. These results indicate that the species H[Pdot]O₂ ^- is irregular tetrahedral in shape, the unpaired electron occupying a hybrid σ orbital centred on the phosphorus nucleus.

There is evidence that the radical H[Pdot]O₂ ^- reacts with an adjacent H₂PO₂ ^- ion forming the species O₂[Pdot]-PHO₂ ⁼. The principal values of the hyperfine interaction tensors of the two phosphorus nuclei are 1365, 944, 921 Mc/s and 527, 362, 359 Mc/s respectively. The proton has an isotropic hyperfine coupling of 90 Mc/s. The spectra of irradiated deuterated crystals confirmed this analysis.     

E.S.R. spectra of X-irradiated methylene diphosphonic acid

X-irradiation of single crystals of methylene diphosphonic acid gives rise to E.S.R. spectra which have been assigned to (OH)₂(O)P-?H₂ and

The former species is the more abundant of the two and the methylene group undergoes rapid re-orientation about a two-fold axis at room temperature but is stationary at 77 K. The ¹H and ³¹P coupling constants in this radical are very similar to those in Ph₃P⁺CH₂, and support the previous conclusions [1] that there is little delocalization of the unpaired electron to the phosphorus atom.     

The E.S.R. spectrum of the tropolonyl radical

The many-body diagrammatic Rayleigh-Schrödinger perturbation theory (RSPT) is used for the calculation of ionization potentials of open-shell systems with one unpaired electron. This theoretical approach is tested on the simple examples of NO₂ and NF₂ molecules described by the INDO semi-empirical hamiltonian. The first- and second-order results are presented.     

Isomeric Cl(2)O(2)(+) and Cl(2)O(2)(-) ions

Charged species structurally related to several isomers of Cl(2)O(2), of considerable importance in atmospheric chemistry, were obtained by chemical ionization (CI) and characterized by collisionally activated dissociation (CAD) mass spectrometry. The ClOClO(+) and [Cl(2)-O(2)](+) species were prepared by positive ion Cl(2)/CI of ClO(2) and O(2), respectively, whereas the ClClO(2)(+) isomer proved an elusive species of considerably lower stability. The ClClO(2)(-) anion was obtained from the negative ion Cl(2)/CI of ClO(2). The formation process, structure and stability of the ions are discussed in connection with available theoretical results and related to the recent preparation of (Cl(2)O(2))(+)SbF(6)(-) and (Cl(2)O(2))(+)Sb(2)F(11)(-) salts in the solid phase. Copyright 1999 John Wiley & Sons, Ltd.     

A study by E.S.R. of Mn2+ in potassium chromate

Divalent manganese ions are found in potassium chromate single crystals after heating at 600°C in the presence of iodine. These ions occupy three differently oriented sites with the same spin Hamiltonian parameters: g_z = 2·000, g_x = 2·008, g_y = 2·015; A_z = ?88·4 G, A_x = A_y = ?91 G; D = 190 and E = ?30 G.The authors suggest that Mn²⁺ occupies a substitutional (K⁺) position rather than an interstitial one. The influence of iodine is discussed.     

E.S.R. study of the conformational kinetics of a biradical

Intramolecular motion in the biradical N,N'-bis(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)ethylenediamine which contains two ionizable amine groups has been studied by E.S.R. spectroscopy. The line-shapes of the spectra as a function of pH and temperature were analysed by density matrix methods to give values for rates and free-energies of activation.     

Anomalous diamagnetic transitions in Ba2Cu3O4Cl2 and Sr2Cu3O4Cl2 antiferromagnets

The magnetic properties of Ba₂Cu₃O₄Cl₂ and Sr₂Cu₃O₄Cl₂ oxychlorides have been studied. A spontaneous manifestation of diamagnetism has been found at quasi-zero and low fields. The temperature of these transitions coincides with the temperature of the antiferromagnetic ordering in Ba₂Cu₃O₄Cl₂ (T _NI ≈ 337 K) and Sr₂Cu₃O₄Cl₂ (T _NI ≈ 386 K). The recorded diamagnetic signal is ?10^?4 emu. It is comparable with the percentage of the superconducting phase in the sample. It is supposed that the arising superconductivity is due to the formation of the superconducting clusters with the direct overlap of the copper d orbitals owing to the frustration processes.     

E.S.R. Study of copper and silver N,N-dialkyldiselenocarbamates

Single crystal E.S.R. studies of Cu(II) and Ag(II) dialkyldiselenocarbamates, diluted in the corresponding Ni(II) complexes, are reported. A method has been developed which removes the necessity to measure the spectra on the same single crystal and in three mutually orthogonal planes. Equations have been derived for the resonance fields and the transition probabilities, taking into account the full spin hamiltonian and without assuming coinciding tensor axes. Applying these equations the g tensor and the metal hyperfine and quadrupole coupling tensors are obtained in high precision. In contrast to the situation in the corresponding dithiocarbamates, it was found for all diselenocarbamates studied that the axes of the g and metal hyperfine tensor do not coincide and that the relative orientation depends on the central metal ion and on the molecular symmetry. The highest g value was always found in the molecular plane, whereas in the dithiocarbamates the highest value is found perpendicular to the molecular plane. The spectra reveal the presence of two sets of two equivalent Se atoms, so that the molecule has inversion symmetry. Especially from the measured ⁷⁷Se hyperfine splittings it could be concluded that the built in guest molecule accepts the structure of the host crystal. Also measurements are reported on powders, glasses and liquid solutions. Evidence has been obtained that in the latter two media the g and metal hyperfine principal axes coincide.     

E.S.R. study of copper and silver N,N-dialkyldiselenocarbamates

Single-crystal E.S.R. studies of Cu(II) diethyldiselenocarbamate and Cu(II) diethyldithiocarbamate, diluted in the corresponding Zn(II) complexes, are reported. The pure copper and zinc crystals consist of dimeric units. When copper is built into the zinc lattice, dimers are formed with one copper and one zinc atom. The g-tensor, the metal hyperfine and quadrupole coupling tensors and also the hyperfine coupling tensors of the ligand selenium atoms have been obtained. Especially, from the measured selenium hyperfine couplings, it could be concluded that the guest molecules do not accept the structure of the host crystal, but have a structure similar to that of the pure copper compound. This is in contrast to the situation in systems where monomeric host crystals (e.g. nickel (II) complexes) are used and where it is found that the guest molecules do accept the structure of the host. As in the monomeric diselenocarbamate systems, in these dimers the principal axes of the g and metal hyperfine coupling tensor do not coincide. In the dimers a rotation of the hyperfine principal axes has taken place in the plane of the molecule, while a rotation of the g-tensor axes in a plane perpendicular to the molecule is typical for the monomeric systems.