Methyl anion trans effect

Methyl anion (CHs"), see also Carbanions gas phase, 109 trans effect, 181... 

Methyl esters undergo trans-esterification with the quaternary ammonium salts at high temperature and the reaction has been used with some effect for the preparation of, for example, n-butyl esters by heating the methyl ester with tetra-n-butylammo-nium chloride at 140°C [31]. Optimum yields (>75%) are obtained in HMPA or in the absence of a solvent. A two-step (one-pot) trans-esterification under phase-transfer catalysed conditions in which the carboxylate anion generated by initially hydrolysis of the ester is alkylated has been reported for Schiff s bases of a-amino acids [32] and for A-alkoxycarbonylmethyl [1-lactams [33]. Direct trans-esterification of methyl and ethyl esters with alcohols under basic catalytic conditions occurs in good yield in the presence of Aliquat [34, 35]. 

As has been clearly demonstrated by X-ray studies (Section III,B), complexation of a salt by a cryptand results in cation-anion separation or dissociation. This enhances anionic reactivity and may effect solubilization of the salt in organic solvents. For example the highly hindered ester methyl mesitoate, 13, may be smoothly hydrolyzed by powdered potassium hydroxide in dry benzene in the presence of [2.2.2] (98). Indeed cryptands have proved particularly useful in phase-trans-... 

Spectroscopic methods can be used to specify the position of donors and acceptors before photoexcitation [50]. This spatial arrangement can obviously influence the equilibrium eomplexation in charge transfer complexes, and hence, the optical transitions accessible to such species [51]. This ordered environment also allows for effective separation of a sensitizing dye from the location of subsequent chemical reactions [52], For example, the efficiency of cis-trans isomerization of A -methyl-4-(p-styryl)pyridinium halides via electron transfer sensitization by Ru(bpy) + was markedly enhanced in the presence of anionic surfactants (about 100-fold) [53], The authors postulate the operation of an electron-relay chain on the anionic surface for the sensitization of ions attached electrostatically. High adsorptivity of the salt on the anionic micelle could also be adduced from salt effects [53, 54]. The micellar order also influenced the attainable electron transfer rates for intramolecular and intermolecular reactions of analogous molecules (pyrene-viologen and pyrene-ferrocene) solubilized within a cationic micelle because the difference in location of the solubilized substances affects the effective distance separating the units [55]. 

Metal-nitrogen distances, as observed in a very large number of crystal structure determinations, are almost the same as those observed for the azole ligands (see Table 2) within experimental error. Comparing pyridine with substituted ligands, it is observed that substituents at position 2 (and 6) next to the donor atom have a dramatic effect upon the stoichiometry and properties of the compounds formed. It appears that a stoichiometry M(Rpy)4(anion)2 with a trans orientation of the anions is not possible, because the methyl group effectively blocks the axial coordination sites. This results in square-planar low-spin compounds for Ni and tetrahedral geometry for some other metals such as Co " and... 

Matsumoto, H. Sakaebe, H. Tatsumi, K., Li/LiCo02 Cell Performance Using Ionic Liquids Composed of N,N-Diethyl-N-methyl-N-(2-methoxyethyl)ammonium - Effect of Anionic Structure, ECS Trans., 2009,16(35), 59-66. 

Khan, M.N., Dahiru, M., Naaliya, J. Effects of anionic micelles on intramolecular general base-catalyzed aminolysis of phenyl and methyl salicylates. J. Chem. Soc., Perkin Trans. 2. 1989, 623-628. 

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