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 .     

Effect of long-chain branching on the relation between steady-flow and dynamic viscosity of polyethylene melts

The steady-state viscosity η, the dynamic viscosity η′, and the storage modulus G′ of several high-density and low-density polyethylene melts were investigated by using the Instron rheometer and the Weissenberg rheogoniometer. The theoretical relation between the two viscosities as proposed earlier is:\documentclass{article}\pagestyle{empty}\begin{document}$ \eta \left( {\dot \gamma } \right){\rm } = {\rm }\int {H\left( {\ln {\rm }\tau } \right)} {\rm }h\left( \theta \right)g\left( \theta \right)^{{\raise0.7ex\hbox{$3$} \!\mathord{\left/ {\vphantom {3 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}} \tau {\rm }d{\rm }\ln {\rm }\tau $\end{document}, where \documentclass{article}\pagestyle{empty}\begin{document}$ \theta {\rm } = {\rm }{{\dot \gamma \tau } \mathord{\left/ {\vphantom {{\dot \gamma \tau } 2}} \right. \kern-\nulldelimiterspace} 2} $\end{document}; \documentclass{article}\pagestyle{empty}\begin{document}$ {\dot \gamma } $\end{document} is the shear rate, H is the relaxation spectrum, τ is the relaxation time, \documentclass{article}\pagestyle{empty}\begin{document}$ g\left( \theta \right){\rm } = {\rm }\left( {{2 \mathord{\left/ {\vphantom {2 \pi }} \right. \kern-\nulldelimiterspace} \pi }} \right)\left[ {\cot ^{ - 1} \theta {\rm } + {\rm }{\theta \mathord{\left/ {\vphantom {\theta {\left( {1 + \theta ^2 } \right)}}} \right. \kern-\nulldelimiterspace} {\left( {1 + \theta ^2 } \right)}}} \right] $\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$ h\left( \theta \right){\rm } = {\rm }\left( {{2 \mathord{\left/ {\vphantom {2 \pi }} \right. \kern-\nulldelimiterspace} \pi }} \right)\left[ {\cot ^{ - 1} \theta {\rm } + {\rm }{{\theta \left( {1{\rm } - {\rm }\theta ^2 } \right)} \mathord{\left/ {\vphantom {{\theta \left( {1{\rm } - {\rm }\theta ^2 } \right)} {\left( {1{\rm } + {\rm }\theta ^2 } \right)^2 }}} \right. \kern-\nulldelimiterspace} {\left( {1{\rm } + {\rm }\theta ^2 } \right)^2 }}} \right] $\end{document}. Good agreement between the experimental and calculated values was obtained, without any coordinate shift, for high-density polyethylenes as well as for a low density sample with low n_w, the weight-average number of branch points per molecule. The correlation, however, was poor with low-density samples with large values of the long-chain branching index n_w. This lack of coordination can be related to n_w. The empirical relation of Cox and Merz failed in a similar way.     

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.     

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.     

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.     

Products and mechanism for the OH radical initiated oxidation of acrylonitrile,methacrylonitrile, and allylcyanide in the presence of NO

The photooxidation of acrylonitrile, methacylonitrile, and allylcyanide in the presence of NO was studied in parts per million concentration using the long-path Fourier transform IR spectroscopic method. The stoichiometry of the OH radical initiated oxidation of methacrylonitrile was established as \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm C}\left( {{\rm CH}_{\rm 3} } \right){\rm CN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{1.0} {\rm HCHO + CH}_{\rm 3} {\rm COCN + 2NO}_{{\rm 2}} + \left( {{\rm OH}} \right) $\end{document}. The yield of HCHO for acrylonitrile and allylcyanide was found to be ca. 100 and 80%, and the stoichiometric reactions were assessed to proceed, \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm CHCN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{1.0} {\rm HCHO + HCOCN + 2NO}_{\rm 2} + \left( {{\rm OH}} \right) $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm CHCH}_{\rm 2} {\rm CN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{0.8} {\rm HCHO + HCOCH}{\rm 2} {\rm CN + 2NO}_{\rm 2} + \left( {{\rm OH}} \right) $\end{document}, respectively. These results revealed that the reaction mechanism for these unsaturated organic cyanides are analogous to that of olefins.     

Theoretical study on peroxyl radical additions to methyl‐substituted ethenes

The electrophilic additions of hydroperoxyl (HO$_{2}^{\mbox{\mathversion{bold}$\cdot$}}$) and alkylperoxyl (RO$_{2}^{\mbox{\mathversion{bold}$\cdot$}}$) radicals to substituted ethenes were studied using the AM1 semiempirical molecular orbital (MO) methods at the self‐consistent field/unrestricted Hartree–Fock (SCF/UHF) level. Reactantlike transition states were predicted for the title additions. The reactivity of an alkylperoxyl radical toward ethenes was found to be decreased as the degree of methyl (Me) substitution on the alkyl group of the radical increased. The relative reactivity and regioselectivity in HO$_{2}^{\mbox{\mathversion{bold}$\cdot$}}$ additions to substituted ethenes was suggested to be SOMO (singly occupied)‐HOMO controlled. A good correlation was established between the activation enthalpy $(\Delta H_{f}^{\ast})$ for the studied additions and the Taft polar substituent constants (σ*) of RO$_{2}^{\mbox{\mathversion{bold}$\cdot$}}$. The Evans–Polanyi correlation between $\Delta H^{\mbox{\mathversion{bold}$\cdot$}}_{f}$ and $\Delta H^{\circ}_{r}$ was justified and the validity of the Hammond postulate was indicated. The calculated results were compared with the available experimental data. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 761–771, 2000     

Relaxation spectra of polymer melts from relaxation and steady-state flow data

Accurate measurements of stress relaxation after steady-state flow have been carried out, in the Newtonian flow region, for a polystyrene and a poly(methyl methacrylate) melt, with a cone-and-plate rotational rheometer. From the stress relaxation σ(t) versus t curves the relaxation spectra H were calculated by means of the first approximation equation: \documentclass{article}\pagestyle{empty}\begin{document}$ H = - ({1 \mathord{\left/ {\vphantom {1 {\dot \gamma t)d\sigma {{(t)} \mathord{\left/ {\vphantom {{(t)} d}} \right. \kern-\nulldelimiterspace} d}}}} \right. \kern-\nulldelimiterspace} {\dot \gamma t)d\sigma {{(t)} \mathord{\left/ {\vphantom {{(t)} d}} \right. \kern-\nulldelimiterspace} d}}}\ln t $\end{document}. The shear stress–shear rate curves, σ versus \documentclass{article}\pagestyle{empty}\begin{document}$ {\dot \gamma } $\end{document} were also measured, in large ranges of shear rates, for the same melts, and from these data the relaxation spectra H were obtained by means of equations given by Faucher and Ferry. The Faucher equation, \documentclass{article}\pagestyle{empty}\begin{document}$ H = - \dot \gamma ^2 d{\sigma \mathord{\left/ {\vphantom {\sigma d}} \right. \kern-\nulldelimiterspace} d}\dot \gamma ^2 $\end{document}, has been found to give results which compare satisfactorily with those obtained from the first approximation equation. It has been found that the Ferry equation has to be modified for comparable agreement.     

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.     

Charge transfer interaction and electrical conductivity of poly(vinyl acetals) containing dispersed TCNQ radical anion salts

Charge transfer (CT) interaction is described in semiconducting dispersions of TCNQ complex salt \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Et}_3 {\rm NH}^+ ({\rm TCNQ})_2^{\cdot^{\hskip-3.7pt\hbox{--}}}$\end{document} with and without added TCNQ°, in poly(vinyl acetal) matrices in which the electron-donor moiety is varied. The extent of CT interaction was determined in films and in solution (DMF, acetonitrile, or methylene chloride) through the absorbances at 398 nm (\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm TCNQ}{\ }^{\cdot^{\hskip-3.7pt\hbox{--}}}$\end{document} and TCNQ°) and 857 nm \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm TCNQ}{\ }^{\cdot^{\hskip-3.7pt\hbox{--}}}$\end{document}. Resistivity of the conductive films was related to the stoichiometry of TCNQ species in the films and found to have a minimum at \documentclass{article}\pagestyle{empty}\begin{document}$[{\rm TCNQ}^\circ]/[{\rm TCNQ}{\ }^{\cdot^{\hskip-3.7pt\hbox{--}}}]\simeq 1$\end{document}. Lower resistivities were attained with films having a uniform, densely packed dispersion of microcrystallites which were obtained at a relatively slow solvent removal rate. With this particular complex salt, strong electron-donor polymers are found to be better matrices for semiconductivity.     

Cross Conjugated Polyenes Derived from 2-Vinyl-butadiene: Electronic States of their Radical Cations,and Triplet Energy

The doublet states of the radical cations of the cross conjugated polyenes 4,4-dimethyl-1-methylidene-2,5-cyclohexadiene 2 and its bis-derivative 1 have been investigated by photoelectron spectroscopy and by electronic spectroscopy of \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{+\kern-4pt {.} } $\end{document}⁺, prepared at 77 K in an electron scavenging matrix by γ-irradiation. Simultaneous consideration of the spectral results shows \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{+\kern-4pt {.} } $\end{document} to be the second hydrocarbon molecular cation (after 2,2-dimethyl isoindene) which possesses a first excited doublet state (D₁) of non-Koopmans nature (²B_3g). The first Koopmans-type excited state (²B_2g) expected from PE. spectroscopy lies, however, very close in energy. In addition T₁ of 1 was observed by electron energy loss spectroscopy at 2.0±0.1 eV. Application of the ‘SDT-equation’ predicts for this state only 1.05 eV; there is at present no reasonable explanation for this failure.     

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.     

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.     

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.     

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.