New pi-delocalized persistent radicals

Progress in the theoretical and experimental investigation of heterocyclic radicals suitable for incorporation into the structure of a liquid crystalline molecule is described. Five classes of heterocyclic systems are discussed, including their methods of preparation, stability and further functionalization to form potentially mesogenic materials.     

Chemical Manganese Dioxide (CMD): its application to the oxidative iodination of benzene, halobenzenes and some deactivated arenes

After comparing our previous and newer results for numerous oxidative aromatic iodination experiments using various brands of active MnO2 as the oxidants,we recommend the use of a Chemical Manganese Dioxide (Aldrich CMD; 90 +% MnO2) as the oxidant of choice, since it is satisfactorily pure and chemically active, and is notably less costly than other options.     

The bioequivalence study of baclofen and lioresal tablets using capillary electrophoresis

A simple and robust analytical method for rapid separation and sensitive quantification of baclofen in human plasma by capillary electrophoresis technique was developed. Electrophoretic separation was optimized and successfully performed using simple sodium tetraborate aqueous solution. Observed detection limit in biological material was 10 ng. Using UV detection at 200 nm excellent linearity (r = 0.999) was observed over the concentration range from 0.025 to 1.0 microg mL(-1). The described method has been validated and applied to the quantitative determination of baclofen in human plasma. The bioavailability of Baclofen (Polpharma) and Lioresal (Novartis) in 18 healthy volunteers was investigated. The results indicate bioequivalence of the reference and Baclofen preparations.     

Banach spaces of continuous functions with few operators

We present two constructions of infinite, separable, compact Hausdorff spaces K for which the Banach space C(K) of all continuous real-valued functions with the supremum norm has remarkable properties. In the first construction K is zero-dimensional and C(K) is non-isomorphic to any of its proper subspaces nor any of its proper quotients. In particular, it is an example of a C(K) space where the hyperplanes, one co-dimensional subspaces of C(K), are not isomorphic to C(K). In the second construction K is connected and C(K) is indecomposable which implies that it is not isomorphic to any C(K) for K zero-dimensional. All these properties follow from the fact that there are few operators on our C(K)s. If we assume the continuum hypothesis the spaces have few operators in the sense that every linear bounded operator T : C (K) C (K) is of the form gI+S where gC(K) and S is weakly compact or equivalently (in C(K) spaces) strictly singular.While conducting research leading to the results presented in this paper, the author was partially supported by a fellowship Produtividade em Pesquisa from National Research Council of Brazil (Conselho Nacional de Pesquisa, Processo Número 300369/01-8). The final stage of the research was realized at the Fields Institute in Toronto where the author was supported by the State of São Paulo Research Assistance Foundation (Fundação de Amparoá Pesquisa do Estado de São Paulo), Processo Número 02/03677-7 and by the Fields Institute.Revised version: 29 January 2004     

A Lindelöf space with no Lindelöf subspace of size

A consistent example of an uncountable Lindelöf (and hence normal) space with no Lindelöf subspace of size is constructed. It remains unsolved whether extra set-theoretic assumptions are necessary for the existence of such a space. However, our space has size and is a -space, i.e., 's are open, and for such spaces extra set-theoretic assumptions turn out to be necessary.

     

Ketene-forming eliminations from aryl phenylacetates promoted by R2NH/R2NH2+ in aqueous MeCN. Mechanistic borderline between E2 and E1cb

Elimination reactions of 2-X-4-NO2C6H3CH2C(O)OC6H3-2-Y-4-NO2 [X = H (1), NO2 (2)] promoted by R2NH/R2NH2+ in 70 mol % MeCN(aq) have been studied kinetically. The base-promoted eliminations from 1 proceeded by the E2 mechanism when Y = Cl, CF3, and NO2. The mechanism changed to the competing E2 and E1cb mechanisms by the poorer leaving groups (Y = H, OMe) and to the E1cb extreme by the strongly electron-withdrawing beta-aryl group (2, X = NO2). The values of beta = 0.14 and beta(lg) = 0.10-0.21 calculated for elimination from 1 (Y = NO2) indicate a reactant-like transition state with small extents of proton transfer and C(alpha)-OAr bond cleavage. The extent of proton transfer increased with a poorer leaving group, and the degree of leaving group bond cleavage increased with a weaker base. Also, the changes in the k(1) and k(-1)/k(2) values with the reactant structure variation are consistent with the E1cb mechanism. From these results, a plausible pathway of the change of the mechanism from E2 to the E1cb extreme is proposed.     

Homogeneous and heterogeneous micropore structures in carbonaceous adsorbents--twenty years later

The major aim of this study is to show that, developed by Dubinin and Stoeckli, the relation between the parameters of DA (Dubinin-Astakhov) and DRS (Dubinin-Radushkevich-Stoeckli) equations is an approximation. It is shown that the parameter B(0) of DRS isotherm should be taken into account in such a relationship; strictly speaking, the parameter n(DA) of DA adsorption isotherm equation is not only the function of the dispersion of the heterogeneity of carbon, it also depends on the location of the maximum of the distribution of this heterogeneity. Moreover, taking into account that the DR isotherm rather does not describe the adsorption in a homogeneous micropore system, the analogous relationship, however, for DA adsorption isotherm as a local equation in GAI (General Adsorption Isotherm) is proposed.     

Polyolefin Macroradical Properties: A Semiempirical Quantum Chemistry Study

Summary: Semiempirical quantum chemistry simulations have been used to estimate the properties of mid‐chain alkyl radicals of ethylene, propylene and styrene oligomers depending on the chain length. The values of spin density and charge on the radical site proved to be almost unchanged for oligomer radicals having from 2 to 11 repeated units. Bond strength parameters of bonds neighboring the radical site demonstrate stable values starting from pentamers. The reliable inference is that the electron structure of polyethylene, poly(propylene) and polystyrene (PS) macroradicals may be simulated by means of relatively short oligomers. The obtained data indicate clearly that the polystyrene tertiary alkyl radical has noticeably decreased values of both spin and charge onto the radical site as well as very decreased strength of β‐bonds. For that reason the PS tert‐alkyl radical is estimated as that having decreased activity and increased susceptibility to chain scission. The most probable cause is delocalization of the free electron onto the neighboring aromatic ring.

Spin density distribution in tertiary radical of polystyrene.     

Two pathways of initiation in the intermolecular iodine atom transfer addition reaction (I‐ATRA) initiated by AIBN

Detection of 4‐iodo‐2,2‐dimethyloctanenitrile and 2‐iodo‐2‐methylpropanenitrile proved an operation of two types (I and II) of initiation in the I‐ATRA reaction. 4‐Iodo‐2,2‐dimethyloctanenitrile, resulting from the isobutyronitrile radical attack onto 1‐hexene followed by the iodine atom transfer (type II), was formed in reactions of EWG‐CH(R)‐I [R = H, Me; EWG = (EtO)₂P(O), (−)−(MenthylO)₂ P(O), CN, Br‐C₆H₄C(O), MeO(O)C, allyl] with 1‐hexene. Nitriles of analogous structures were also detected in reactions of (EtO)₂P(O)CH(R)‐I with 1‐heptene, 1‐heptyne, cyclopentene, cyclohexene, and propargyl alcohol. 2‐Iodo‐2‐methylpropanenitrile as the product of the isobutyronitrile attack onto iodine atom of the starting iodide was detected for the first time in the reaction of allyl iodide and 1‐hexene and proved an operation of the cooperating pathway of initiation (type I). EPR experiments, performed directly in the spectrometer cavity, confirmed extremely low concentration of reacting radical species (for a sample of c = 0.1 mol/dm³, <10⁻⁸ mol/dm³, or <10⁻¹² moles of spins in a sample) in I‐ATRA reactions involving low reactive 1‐iodoalkylphosphonates. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:246–253, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20116