Methyl anion INDEX

A theoretical study at a HF/3-21G level of stationary structures in view of modeling the kinetic and thermodynamic controls by solvent effects was carried out by Andres and coworkers [294], The reaction mechanism for the addition of azide anion to methyl 2,3-dideaoxy-2,3-epimino-oeL-eiythrofuranoside, methyl 2,3-anhydro-a-L-ciythrofuranoside and methyl 2,3-anhydro-P-L-eiythrofuranoside were investigated. The reaction mechanism presents alternative pathways (with two saddle points of index 1) which act in a kinetically competitive way. The results indicate that the inclusion of solvent effects changes the order of stability of products and saddle points. From the structural point of view, the solvent affects the energy of the saddles but not their geometric parameters. Other stationary points geometries are also stable. 

Ionic liquids are a class of solvents and they are the subject of keen research interest in chemistry (Freemantle, 1998). Hydrophobic ionic liquids with low melting points (from -30°C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also of interest. NMR and elemental analysis have characterized the molten salts. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1,2, 3, and 4(5)-positions on the imidazolium cation on these properties has been scrutinized. Viscosities as low as 35 cP (for l-ethyl-3-methylimi-dazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of l-ethyl-3-methyl-imidazolium bis((trifluoromethyl)sulfonyl)amide. The hydrophobic molten salts are promising solvents for electrochemical, photovoltaic, and synthetic applications (Bon-hote et al., 1996). 

To give an impression of the nature of useful experimental results, some flow birefringence measurements which were obtained on a solution of polystyrene in methyl 4-bromo-phenyl carbinol, are reproduced in Figs. 1.2 and 1.3. The concentration of the solution was 2 wt. percents, measuring temperatures are indicated in the figures. The special polystyrene used was a well-known sample of anionically polymerized polystyrene, viz. S 111, provided by the courtesy of Dow Chem. Corp. Its molecular weight is 224,000. The indicated solvent is, at 18 °C, a 0-solvent and possesses practically the same refractive index as polystyrene itself (32). The measurement results are kindly provided by Daum from his still unpublished work. 

Lignin has been grafted with ethenylbenzene [43,44] (styrene), 4-methyl-2-oxy-3-oxopent-4-ene [45,46] (methylmethacrylate), 2-propenamide (acrylamide), 2-propene nitrile [47] (acrylonitrile), cationic monomers, anionic monomers, and propenoic acid ethoxylates. An index of compounds listing structure, product name, and trivial name is given in Table 3. Two types of... 

The ratio M IMn approaches unity asymptotically as increases. Narrow molecular weight distributions should thus be obtained in living ionic polymerizations with fast initiation in the absence of depropagation, termination, and chain transfer reactions. Values of polydispersity index (PDI) below 1.1 -1.2 are indeed found for many living polymerizations. Molecular weight-standards for polystyrene, poly-isoprene, poly(a-methylstyrene), and poly (methyl methacrylate) are thus synthesized by living anionic polymerizations. However, the termination reactions in methyl methacrylate polymerizations and depropagation in or-methylstyrene polymerizations tend to broaden the PDI in these systems. 

Soum and Fontanille report that di-s-butyl magnesium generates living polymer from 2-vinylpyridine without the involvement of the side-reactions that afflict the polymerization initiated by alkali metal alkyls the resulting polymer has an isotacticity index of 0.9. Arai et al. have synthesized styrene-butadiene-4-vinylpyridine triblock copolymers. Hogen-Esch et a/. have continued their study of the stereochemistry of the anionic polymerization of 2-vinylpyridine in THF solution. Oligomers were synthesized by addition of alkali salts of 2-ethylpyridine to 2-vinylpyridine termination was effected by reaction with methyl iodide. Highly isotactic products were obtained with U and Na as counterions but with K or Rb there was no stereoselection. Epimerization resulted in the expected statistical mixtures of stereoisomers and it was concluded that stereoselection is kinetically controlled. 

The molecular weight of each component in a polymer blend may also be determined. In a model experiment, poly(methyl methacrylate), PMMA, molecular weights were estimated in the presence of polystyrene, PS (90). Anion-ically polymerized polystyrene and free radically polymerized poly(methyl methacrylate) were dissolved in tetrahydrofuran in a 50/50 w/w mix. A dual detector GPC was used, equipped with refractive index (RI) and ultraviolet (UV) detectors. 

Montalban MG, Bolivar CL, Bnos FGD, Villora G (2015) Effect of temperature, anion, and alkyl chain length on the density and refractive index of l-alkyl-3-methyl-imidazolium-based ionic liquids. J Chem Eng Data 60 1986-1996... 

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