ESR study of free radicals produced in polyethylene irradiated by ultraviolet light

ESR studies of ultraviolet-irradiated polyethylene (PE) were carried out. Irradiation effects different from those of high-energy radiation are observed. Ultraviolet radiation is absorbed selectively, and especially in carbonyl groups in PE produced by oxidation. Radicals produced were identified as \documentclass{article}\pagestyle{empty}\begin{document}$ \hbox{---} {\rm CH}_2 \hbox{---} {\dot {\rm C}} {\rm H} \hbox{---}{\rm CHO}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \hbox{---} {\rm CH}_2 \hbox{---} {\dot {\rm C}} {\rm H} \hbox{---}{\rm CH}_2 \hbox{---}$\end{document}. Some radicals giving a quintet signal stable at room temperature were also observed but remained unidentified. The radical \documentclass{article}\pagestyle{empty}\begin{document}$ \hbox{---} {\rm CH}_2 \hbox{---} {\dot {\rm C}} {\rm H} \hbox{---}{\rm CHO}$\end{document} undergoes a mutual conversion with the acyl radical:      

Shear thinning and polymer deformation in large flow fields

We theoretically investigate polymer deformation and shear thinning, i.e., a decrease of intrinsic viscosity, in a dilute polymer solution as a function of the applied shear rate $ \dot \gamma $. We use a bead-and-spring model with hydrodynamic interaction in the Rouse-Zimm framework, approximately accounting also for excluded-volume effects, and impose a constraint on the average mean-square spring length to prevent its stretching at large $ \dot \gamma $. When suitably normalized, both the intrinsic viscosity [η] and the components of the mean gyration tensor 〈SS〉 depend on the single variable $ \xi = {{\dot \gamma \tau _1^{\left( 0 \right)} } \mathord{\left/ {\vphantom {{\dot \gamma \tau _1^{\left( 0 \right)} } {N^{1 - v} }}} \right. \kern-\nulldelimiterspace} {N^{1 - v} }} $ where τ is the longest relaxation time for $ \dot \gamma = 0 $, N is the number of chain springs and v is the Flory exponent. The full shear-rate dependence is obtained numerically, and compared with analytical results obtained under free-draining conditions both for low and for very large shear rates. The shortcomings of the theory are also discussed, in particular a substantial stretching under shear of the central springs, where the intramolecular tension is largest, with a corresponding strong contraction of the end springs due to the average character of the constraint.     

Exact solution of the relativistic dynamics of a spin‐½ particle moving in a homogeneous magnetic field

The relativistic dynamics of one spin‐½ particle moving in a uniform magnetic field is described by the Hamiltonian $\mathbf{h}^{0}_{D}(\pi)=c\alpha\cdot\pi+\beta mc^{2}$. The discrete (and semidiscrete) eigenvalues and the corresponding eigenspinors are in principle known from the work of Dirac, Rabi, and Bloch. These are extensively reviewed here. Next, exact solutions are worked out for the recoil dynamics in relative coordinates, which involves the Hamiltonian $\mathbf{h}^{0}_{D}(-\mathbf{k})=-c\alpha\cdot\mathbf{k}+\beta mc^{2}$. Exact solutions are also explicitly calculated in the case where the spin‐½ particle has an anomalous magnetic moment such that its Hamiltonian is given by $\mathbf{h}_{D}(\pi)=\mathbf{h}^{0}_{D}(\pi)-\beta\mu_{\mathrm{ano}}\sigma\cdot\mathbf{B}$. Similar exact solutions are derived here when the recoiling particle has an anomalous magnetic moment, that is, the eigenvalues and eigenspinors of the Hamiltonian $\mathbf{h}_{D}(-\mathbf{k})=\mathbf{h}^{0}_{D}(-\mathbf{k})-\beta\mu_{\mathrm{ano}}\sigma\cdot\mathbf{B}$ are explicitly obtained. The diagonalized and separable form of the Hamiltonian h _D(π), written as $\tilde{\mathbf{h}}_{D}(\pi)$, has exceedingly simple forms of eigenspinors. Similarly, the diagonalized and separable form of the operator h _D(? k ), written as $\tilde{\mathbf{h}}_{D}(-\mathbf{k})$, has very simple eigenspinors. The importance of these exact solutions is that the eigenspinors can be used as bases in a calculation involving many spin‐½ particles placed in a uniform magnetic field. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 209–217, 2001     

Rearrangements of Radical Cations of [2.2]Paracyclophanes and of a bridged [14]annulene to those of pyrenes: An ESR and ENDOR study

ESR and ENDOR studies have been carried out on the radical cations obtained consecutively by reaction of trans-10b, 10c-dimethyl-10b, 10c-dihydropyrene ( 4 ) with AlCl₃ in CH₂C1₂. The primarily formed ${\bf 4}^{+ \atop \dot{}}$ rearranges at 253 K to the radical cation(s) of 1,6- ( 5a ) and/or 1,8-dimethylpyrene ( 5b ). At 323 K, the spectra of ${\bf 5a}^{+ \atop \dot{}}$/${\bf 5b}^{+ \atop \dot{}}$ are replaced by that of the highly persistent radical cation of 1,3,6,8-tetramethylpyrene ( 6 ). Surprisingly, ${\bf 6}^{+ \atop \dot{}}$ is also the only observable paramagnetic product resulting from a treatment of 4,5,7,8- ( 1 ), 4,7,13,16- ( 2 ), and 4,5,12,13-tetramethyl[2.2]paracyclophane ( 3 ) with AlCl₃ in CH₂Cl₂ at 353 K. The structures of the intermediates in the rearrangement [${\bf 1}^{+ \atop \dot{}}$, ${\bf 2}^{+ \atop \dot{}}$, ${\bf 3}^{+ \atop \dot{}}$] → ${\bf 6}^{+ \atop \dot{}}$ are discussed.     

Structures and formation of \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm C}_{{\rm 4}} {\rm H}_{{\rm 8}} } \right]_{}^{_.^ + } $\end{document} ions

Several \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm C}_{{\rm 4}} {\rm H}_{{\rm\ 8}} } \right]_{}^{_.^ + } $\end{document} ion isomers yield characteristic and distinguishable collisional activation spectra: \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm 1-butene} } \right]_{}^{_.^ + } $\end{document} and/or \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm 2-butene} } \right]_{}^{_.^ + } $\end{document} (a-b), \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm isobutene} } \right]_{}^{_.^ + } $\end{document} (c) and [cyclobutane]⁺ (e), while the collisional activation spectrum of \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm methylcyclopropane} } \right]_{}^{_.^ + } $\end{document} (d) could also arise from a combination of a-b and c. Although ready isomerization may occur for \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm C}_{{\rm 4}} {\rm H}_{{\rm 8}} } \right]_{}^{_.^ + } $\end{document} ions of higher internal energy, such as d or e → a, b, and/or c, the isomeric product ions identified from many precursors are consistent with previously postulated rearrangement mechanisms. 1,4-Eliminations of HX occur in 1-alkanols and, in part, 1-buthanethiol and 1-bromobutane. The collisional activation data are consistent with a substantial proportion of 1,3-elimination in 1- and 2-chlorobutane, although 1,2-elimination may also occur in the latter, and the formation of the methylcycloprpane ion from n-butyl vinyl ether and from n-butyl formate. Surprisingly, cyclohexane yields the \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm linear butene} } \right]_{}^{_.^ + } $\end{document} ions a-b, not \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm cyclobutane} } \right]_{}^{_.^ + } $\end{document}, e.     

Study of crosslink formation by partial conversion properties. IV. Copolymerization of styrene with poly(ethylene fumarate)

The mechanism of the crosslinking reaction in the copolymerization of poly(ethylene fumarate) and styrene has been studied by using partial conversion number-average molecular weights and viscosities. In dilute solution the reaction is mainly the formation of intramolecular crosslinks, illustrated by a reduced dependence of \documentclass{article}\pagestyle{empty}\begin{document}$\overline{\overline M}_n$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$[\overline{\overline \eta}]$\end{document} on conversion. Increasing the monomer concentrations increases the contribution from intermolecular reactions and gives a much greater dependence of \documentclass{article}\pagestyle{empty}\begin{document}$\overline{\overline M}_n$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$[\overline{\overline \eta}]$\end{document} on conversion.     

Méthodes chimiques d'analyse des polyacroléines linéaires

Linear polyacroleins prepared by anionic polymerization give the structural repeat units of the types \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--}[{\rm CH}\left( {{\rm CHO}} \right)\hbox{--} {\rm CH}_{\rm 2} {\rm \rlap{--} ], \rlap{--} [CH}_{\rm 2} \hbox{--} {\rm CH}\left( {{\rm CHO}} \right)\rlap{--} ], $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} [{\rm CH}\left( {{\rm CH}\hbox {\rm CH}_2 } \right)\hbox{\rm O\rlap{--} ]} $\end{document} without any cyclization. Analysis of these polymers by several methods reveal the nature and amount of each structural species, and an estimation of their distribution along the polymeric chain.     

Assigning structures to [C2H3O]+ ions

The problem of assigning structures to [C₂H₃O]⁺ ions produced from a wide variety of precursor molecules has been readdressed. The identification of the acetyl cation, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{O}} $\end{document}, from metastable peak characteristics and collisional activation mass spectra appears to be straightforward. The structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{2}} = \mathop {\rm{C}}\limits^{\rm{ + }} - {\rm{OH}} $\end{document} is also known to exist as a stable ion. A third ion, whose structure may be represented as \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm{C}}\limits^{\rm{ + }} {\rm{H}}_{\rm{2}} {\rm{CHO}} $\end{document} or has also been characterized.     

Differentiation of tautomers by ion cyclotron resonance spectrometry: \documentclass{article}\pagestyle{empty}\begin{document}${\rm (CH}_{\rm 3} {\rm)}_{\rm 2} \mathop {\rm N}\limits^{\rm + } {\rm = CH}_{\rm 2} {\rm vs H}_{\rm 3} {\rm C}\mathop {\rm N}\limits^{\rm + } {\rm H = CHCH}_{\rm 3}$\end{document}

Ion cyclotron resonance spectrometry and deuterium labeling have been used to determine that nondecomposing \documentclass{article}\pagestyle{empty}\begin{document}${\rm (CH}_{\rm 3} {\rm)}_{\rm 2} \mathop {\rm N}\limits^{\rm + } {\rm = CH}_{\rm 2}$\end{document} ions do not isomerize to \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 3} {\rm CH = }\mathop {\rm N}\limits^{\rm + } {\rm HCH}_{\rm 3}$\end{document}.     

Rearrangement of the Radical Anions of 1,6-Bridged[10]Annulenes to Derivatives of 5H-Benzocycloheptene and Benzotropylium

The rearrangement products obtained upon reduction of 1,6-methano[10]-annulene ( 1 ) and its 11-halogen derivatives have been studied by ESR. and, in part, by ENDOR. spectroscopy. These derivatives comprise 11,11-difluoro- ( 2 ), 11-fluoro- ( 3 ), 11,11-dichloro- ( 4 ) and 11-bromo-1,6-methano[10]annulene ( 5 ), as well as the 2,5,7,10-tetradeuteriated compounds 2 -D₄ and 3 -D₄. The studies of the secondary products in question have been initiated by the finding that the radical anion of 11,11-dimethyltricyclo[4.4.1.0^1,6]undeca-2,4,7,9-tetraene ( 12 ), i.e., the prevailing valence isomer of 11,11-dimethyl-1,6-methano[10]annulene, undergoes above 163 K a rearrangement to the radical anion of 5,5-dimethylbenzocycloheptene ( 14 ). A rearrangement of this kind also occurs for the radical anion of the parent compound 1 , albeit only above 323 K. The lower reactivity of 1 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} relative to 12 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is rationalized by the assumption that the first and rate determining step in the case of 1 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is the valence isomerization to the radical anion of tricyclo[4.4.1.0^1,6]undeca-2,4,7,9-tetraene ( 1a ). In the reducing medium used in such reactions (potassium in 1,2-dimethoxyethane), the final paramagnetic product of 1 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is not 5H-benzocycloheptene ( 15 ), but the benzotropylium radical dianion ( ). This product ( ) is also obtained from the radical anions of the halogen-substituted 1,6-methano[10]annulenes, 2 to 5 , in the same medium. The temperatures required for the conversion of 2 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} into lie above 293 and 243 K, respectively, whereas the short-lived species 4 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 5 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} undergo such a rearrangement already at 163 K. The stability of the four halogen-substituted radical anions thus decreases in the sequence 2 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} > 3 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} > 4 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} ≈ 5 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}. Replacement of 2 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} by 2 -D₄\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3 -D₄\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}, respectively, leads to 1,4,5,8-tetradeuteriobenzotropylium radical dianion ( ). Experimental evidence and theoretical arguments indicate that the rearrangements in question are initiated by a loss of one ( 3 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 5 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}) or two ( 2 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 4 \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}) halogen atoms. Such a reaction step must involve the intermediacy of the radical 19 · (see below) which rapidly isomerizes to the benzotropylium radical 16 :. Support for the transient existence of 19 . is provided by the thermolysis of 1,6-methano [10]annulene-11-t-butylperoxyester (6) which yields 16 . in a temperature dependent equilibrium with a mixture of its dimers ( 16 ₂). In the hitherto unreported ESR. spectra of 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}. and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}, the coupling constants of the ring protons differ considerably from the analogous values for the radical anions of other 1,6-bridged [10]annulenes. These differences strongly suggest that the fluoro-substitution substantially affects the character of the singly occupied orbital.     

The gas phase ion chemistry of the acetyl cation and isomeric [C2H3O]+ ions. On the structure of the [C2H3O]+ daughter ions generated from the enol of acetone radical cation

Methods are described for the unequivocal identification of the acetyl, [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} ?O] (a), 1-hydroxyvinyl, [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH] (b), and oxiranyl, (d), cations. They involve the careful examination of metastable peak intensities and shapes and collision induced processes at very low, high and intermediate collision gas pressures. It will be shown that each [C₂H₃O]⁺ ion produces a unique metastable peak for the fragmentation [C₂H₃O]⁺ → [CH₃]⁺+CO, each appropriately relating to different [C₂H₃O]⁺ structures. [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] ions do not interconvert with any of the other [C₂H₃O]⁺ ions prior to loss of CO, but deuterium and ¹³C labelling experiments established that [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH] (b) rearranges via a 1,2-H shift into energy-rich leading to the loss of positional identity of the carbon atoms in ions (b). Fragmentation of b to [CH₃]⁺+CO has a high activation energy, c. 400 kJ mol^?1. On the other hand, , generated at its threshold from a suitable precursor molecule, does not rearrange into [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH], but undergoes a slow isomerization into [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] via [CH₂\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}HO]. Interpretation of results rests in part upon recent ab initio calculations. The methods described in this paper permit the identification of reactions that have hitherto lain unsuspected: for example, many of the ionized molecules of type CH₃COR examined in this work produce [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH] ions in addition to [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] showing that some enolization takes place prior to fragmentation. Furthermore, ionized ethanol generates a, b and d ions. We have also applied the methods for identification of daughter ions in systems of current interest. The loss of OH^˙ from [CH₃COOD]^+˙ generates only [CH₂?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OD]. Elimination of CH₃^˙ from the enol of acetone radical cation most probably generates only [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] ions, confirming the earlier proposal for non-ergodic behaviour of this system. We stress, however, that until all stable isomeric species (such as [CH₃? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^{\rm + } $\end{document}?C:]) have been experimentally identified, the hypothesis of incompletely randomized energy should be used with reserve.     

Gas permeability and permselectivity of fluorinated polybenzoxazoles

Gas permeability and permselectivity are investigated for polybenzoxazoles from bis(3-amino-4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (BAHHP) and aromatic diacid chlorides. Effects of thermal cyclization on the permeation properties are also investigated. The polybenzoxazole from BAHHP and 4,4′-(1,1,1,3,3,3-hexafluoroisopropylidene)dibenzoyl chloride (HFDB) displays high performance for CO₂/CH₄ separation ( $ {\rm P}_{{\rm CO}_2 } $ = 6.1 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, and $ {{{\rm P}_{{\rm CO}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm CO}_2 } } {{\rm P}_{{\rm CH}_4 } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_4 } }} $ = 38 at 35°C). The polybenzoxazole from BAHHP and 2,6-naphthalene dicarbonyl chloride displays high performance for H₂/CO or H₂/CH₄ separation ( $ {\rm P}_{{\rm H}_2 } $ = 2.4 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CO}} }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CO}} }} $ = 71, and $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CH}_{\rm 4} } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_{\rm 4} } }} $ = 250). Permeation properties for the polybenzoxazole from BAHHP and HFDB are close to those for a polyimide of similar chemical structure. The permeation properties are discussed in connection with packing density and local segmental mobility. © 1992 John Wiley & Sons, Inc.     

Stable γ-distonic oxonium ions: R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCHR′ĊH2CHR″ and their characteristic reaction

The γ-distonic radical ions R$ \mathop {\rm O}\limits^ + $CHR′CH₂?HR″ and their molecular ion counterparts R$ \mathop {\rm O}\limits^{{\rm + } \cdot } $CHR′CH₂CH₂R″ have been studied by isotopic labelling and collision-induced dissociation, applying a potential to the collision cell in order to separate activated from spontaneous decompositions. The stability of CH₃$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?HCH₃, C₂H₅$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?HCH₃, CH₃$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?H₂, CH₃$ \mathop {\rm O}\limits^ + $HCH₂CH₂?HCH₃ and C₂H₅$ \mathop {\rm O}\limits^ + $HCH₂CH₂?HCH₃, has been demonstrated and their characteristic decomposition, alcohol loss, identified. For all these γ-distonic ions, the 1,4-H abstraction leading to their molecular ion counterpart exhibits a primary isotope effect.     

The Radical Ions of Naphtho [1,8-cd]-[1,2,6]thiadiazine and Some of Its Derivatives

The radical cations and anions of naphtho [1,8-cd]-[1,2,6]thiadiazine (1) and 6,7-dihydroacenaphtho [5, 6-cd]-[1,2,6]thiadiazine (2) , as well as the radical anion of acenaphtho [5, 6-cd]-[1,2,6]thiadiazine (3) have been characterized by ESR. spectroscopy. The π-spin distributions in the radical cations \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\oplus \atop \dot{}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{\oplus \atop \dot{}}$\end{document} strongly resemble those in the iso-π-electronic phenalenyl radical. A prominent feature of the radical anions \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{\ominus \atop \dot{}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{\ominus \atop \dot{}}$\end{document} is the substantial localization of the π-spin population on the thiadiazine fragment. These findings are satisfactorily accounted for by HMO models using conventional heteroatom parameters.     

Photoreduction of Thiosulfate in Semiconductor Dispersions

Conduction band electrons produced by band gap excitation of TiO₂-particles reduce efficiently thiosulfate to sulfide and sulfite. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm 2e}_{{\rm cb}}^ - ({\rm TiO}_{\rm 2}) + {\rm S}_{\rm 2} {\rm O}_3^{2 - } \longrightarrow {\rm S}^{2 - } + {\rm SO}_3^{2 - } $\end{document} This reaction is confirmed by electrochemical investigations with polycrystalline TiO₂-electrodes. The valence band process in alkaline TiO₂-dispersions involves oxidation of S₂O to tetrathionate which quantitatively dismutates into sulfite and thiosulfate, the net reaction being: \documentclass{article}\pagestyle{empty}\begin{document}$ 2{\rm h}^{\rm + } ({\rm TiO}_{\rm 2}) + 0.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } + 1.5{\rm H}_{\rm 2} {\rm O} \longrightarrow {\rm SO}_3^{2 - } + 3{\rm H}^{\rm + } $\end{document} This photodriven disproportionation of thiosulfate into sulfide and sulfite: \documentclass{article}\pagestyle{empty}\begin{document}$ 1.5{\rm H}_{\rm 2} {\rm O } + 1.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } \mathop \to \limits^{h\nu} 2{\rm SO}_3^{2 - } + {\rm S}^{{\rm 2} - } + 3{\rm H}^{\rm + } $\end{document} should be of great interest for systems that photochemically split hydrogen sulfide into hydrogen and sulfur.     

Gas phase ion chemistry of methyl acetate,methyl propanoate and their enolic tautomers. An experimental approach

From a combination of isotopic substitution, time-resolved measurements and sequential collision experiments, it was proposed that whereas ionized methyl acetate prior to fragmentation rearranges largely into \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 \mathop {\rm C}\limits^ + ({\rm OH}){\rm O}\mathop {\rm C}\limits^{\rm .} {\rm H}_2 $\end{document}, in contrast, methyl propanoate molecular ions isomerize into \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^. {\rm H}_2 {\rm CH}_2 \mathop {\rm C}\limits^ + ({\rm OH}){\rm OCH}_3 $\end{document}. Metastably fragmenting methyl acetate molecular ions are known predominantly to form H₂?OH together with \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 - \mathop {\rm C}\limits^ + = {\rm O} $\end{document}, whereas ionized methyl propanoate largely yields H₃CO˙ together with \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm CH}_2 - \mathop {\rm C}\limits^ + = {\rm O} $\end{document}. The observations were explained in terms of the participation of different distonic molecular ions. The enol form of ionized methyl acetate generates substantially more H₃CO˙ in admixture with H₂?OH than the keto tautomer. This is ascribed to the rearrangement of the enol ion to the keto form being partially rate determining, which results in a wider range of internal energies among metastably fragmenting enol ions. Extensive ab initio calculations at a high level of theory would be required to establish detailed reaction mechanisms.     

The Radical Anions and Trianions of 1,8-Diphenylnaphthalene and of Some of its Derivatives Containing a Cyclophane Substructure

The radical anions of 1,8-diphenylnaphthalene ( 1 ) and its decadeuterio-(D₁₀- 1 ) and dimethyl-( 2 ) derivatives, as well as those of [2.0.0] (1,4)benzeno(1,8)naphthaleno(1,4)benzenophane ( 3 ) and its olefinic analogue ( 4 ) have been studied by ESR and ENDOR spectroscopy, At a variance with a previous report, the spin population in \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {2}^{-\kern-4pt {.}} $\end{document} is to a great extent localized in the naphthalene moiety. A similar spin distribution is found for \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {3}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {4}^{-\kern-4pt {.}} $\end{document}. The ground conformations of \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document}-\documentclass{article}\pagestyle{empty}\begin{document}$ \rm {4}^{-\kern-4pt {.}} $\end{document} are chiral of C₂ symmetry. For \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document}, an energy barrier between these conformations and the angle of twist about the bonds linking the naphthalene moiety with the phenyl substituents were estimated as ca. 50 kJ/mol and ca. 45°, respectively. The radical trianions of 1 , D₁₀- 1 , and 2 , have also been characterized by their hyperfine data. In \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{3-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {2}^{3-\kern-4pt {.}} $\end{document}, the bulk of the spin population resides in the two benzene rings so that these radical trianions can be regarded as the radical anions of ‘open-chain cyclophanes’ with a fused naphthalene π-system bearing almost two negative charges. The main features of the spin distribution in both \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{3-\kern-4pt {.}} $\end{document} are correctly predicted by an HMO model of 1 .