Asymmetric nitrogen—41: Stereochemistry of bicyclic 1,2-cis-diaziridines

The twisting of 5- and 6-membered rings in bicyclic cis-diaziridines—1,5-diazabicyclo [3.1.0]hexanes 12–17 and l,6-diazabicyclo[4.1.0]heptane 18—is a rapid process in the time scale of ¹H- and ¹³C-NMR even at -80°. According to the ¹H- and ¹³C-NMR spectra, 1,5-diazabicyclo [3.1.0]hexanes 12,13,15a,15b and 16a,16b do, exist mostly in the boat form ; only the introduction of endo substituents into position 3 or 6 leads to the population of the chair, as is the case with 14 and 17. 2,4-Dialkyl substituted 1,5-diaza- and 1,3,5-triazabicyclo[3.1.0]hexanes are formed via a transition cyclization state similar in its geometry to the initial chair-shaped N-chlorodi(tri)azanes.     

Internal conversion as the main stabilization mechanism for long-lived negative molecular ions

The temperature dependence of the mean lifetime of Ph-N=N-Ph^? azobenzene negative molecular ions on the captured electron energy is studied with a static mass spectrometer by the method of resonance electron capture. A family of respective experimental dependences is calculated accurate to 2–10%. It is shown that the molecular anions in the epithermal electron energy range can be stabilized through internal conversion, namely, a series of fast radiationless transitions without change in the multiplicity.     

Thermal electron capture by some chlorobromopropanes

Thermal electron attachment rate constants for CH₂ClCHBrCH₃ and CH₂ClCH₂CH₂Br have been measured using electron swarm method. Corresponding rate constants are equal to 3.5×10^-10 and 2.5×10^-10 cm³ molec^-1 s^-1, respectively. Parallely, negative ion mass spectra of these compounds as well as CH₂FCH₂Br, CH₂ClCH₂Br, CH₂BrCH₂Br and CF₃CHClBr has been measured with negative ion mass spectrometry method. The rate constants have been compared with the negative ion mass spectra.     

On the delay mechanism of Cl<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> diatomic anion dissociation up to the microsecond timescale

The dissociative capture of slow electrons by tetrachlorethylene (C₂Cl₄) has been investigated by resonant electron capture negative ion mass spectrometry. Metastable ions with fractional mass numbers 7.5, 17.5, and 19 corresponding to the C₂Cl₄⁻ → Cl⁻ + C₂Cl₃ and Cl₂⁻ → Cl⁻ + Cl decays occurring at the microsecond timescale have been detected. It has been revealed that Cl₂⁻ anions, which are fragment ions, can dissociate at the microsecond timescale, which is very surprising for a system with one internal degree of freedom. This process is assumingly attributed to the rotational excitation of Cl₂⁻ anions. Thus, the experimental estimate of the time of rovibronic relaxation in the Cl₂⁻ anion has been obtained.     

Formation of color centers and paramagnetic species by alkaline hydrolysis of polydiphenylenesulfophthalide

Blue color centers (CC) (an intense absorption band (AB) at 566 nm and a weaker AB at 350 nm) and paramagnetic species (PMS) that give an ESR singlet withg=2.0028 and δH=10 Oe are formed by the treatment of a DMSO solution of polydiphenylenesulfophthalide with an excess of LiOH. The formation of blue CC is accompanied by a decrease in the intensity of the absorption band of the phenyl groups of the polymer at 270 nm. The blue CC were attributed to quinoid structures like the Chichibabin hydrocarbon. The long-wave absorption at 650–800 nm was assigned to the regions of quinoid-benzoid conjugation. The color centers and PMS were also observed when the polymer was hydrolyzed in cyclohexanone; however, in this case, the reaction was accompanied by polymer aggregation. The electronic spectrum of the Chichibabin hydrocarbon was calculated by the PM3 method. The identity of CC formed by alkaline hydrolysis and appearing in the polymer—aniline—cyclohexanone system was shown. The absence of “quinoid” CC for polyterphenyl sulfophthalide was explained by the energetically unfavorable singlet state for structures similar to the Müller hydrocarbon. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya No. 2, pp. 295–300, February, 2000.     

Propagation of Low-Energy Electrons and the Density of Unoccupied States in Ultrathin TCNQ Layers on the Oxidized Silicon Surface

Physics of the Solid State - The formation of unoccupied electronic states and the boundary potential barrier during thermal deposition of tetracyanoquinodimethane (TCNQ) films to 7 nm in thickness...     

Formation of mono-, bi-, and polyradicals upon reduction of poly(arylenesulfophthalides) by metallic lithium

The reduction of poly(biphenylenesulfophthalide) (1), poly(fluorenylenesulfophthalide) (2), and poly(terphenylenesulfophthalide) (3) by metallic lithium in DMSO was studied using UV-visible and ESR spectroscopies. The reduction of compounds 1 and 2 affords blue diamagnetic color centers with absorption bands at 568 and 350 nm (shoulder) for 1 and at 576 and 360 nm (shoulder) for 2. The color centers were attributed to quinoid structures of the Chichibabin"s hydrocarbon type, being biradicals in the ground singlet state. The spectra of compounds 1 and 2 also exhibit weak absorption bands at 420 nm, which are assigned to monoradicals of the triarylmethyl type. The reduction of compound 3, for which the formation of quinoid structures is energetically unfavorable, leads to polyradicals of the triarylmethyl type with a high content (100%) of unpaired electrons in the main polymer chain. These radicals are characterized by absorption bands at 430 nm (allowed transition) and 638 nm (forbidden transition). The paramagnetic centers in all polymers under study give singlet lines with g = 2.0028 and H 10 Oe in the ESR spectra. The color centers and radicals of the triarylmethyl type observed for the poly(arylenesulfophthalides) under study are assumed to be formed upon the dissociative electron transfer from lithium to the sulfophthalide cycles of the polymeric molecules. The PM3 calculations show a high electron affinity of the sulfophthalide cycle and a higher propensity of the fluorenyl bridge to form quinoid structures than that of the biphenyl bridge.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.