Electrostatic interactions products

Other reactions are controlled kinetically, and the most stable product is not the major one observed. In these cases, you must look at the reactant side of the reaction coordinate to discover factors determining the outcome. Klopman and Salem developed an analysis of reactivity in terms of two factors an electrostatic interaction approximated by atomic charges and a Frontier orbital interaction. Fleming s book provides an excellent introduction to these ideas. 

Tacticity of products. Most solid catalysts produce isotactic products. This is probably because of the highly orienting effect of the solid surface, as noted in item (1). The preferred isotactic configuration produced at these surfaces is largely governed by steric and electrostatic interactions between the monomer and the ligands of the transition metal. Syndiotacticity is mostly produced by soluble catalysts. Syndiotactic polymerizations are carried out at low temperatures, and even the catalyst must be prepared at low temperatures otherwise specificity is lost. With polar monomers syndiotacticity is also promoted by polar reaction media. Apparently the polar solvent molecules compete with monomer for coordination sites, and thus indicate more loosely coordinated reactive species. 

It IS likely that the syn selectivity exhibited in cycloadditions of fluoroallene IS due to electrostatic interactions [23 25] As in the case of difluoroallene the reactions of fluoroallene with diazoalkanes and nitrile oxides are facile, but such reactions, other than that shown in equation 18, are neither regio nor stereospeutic [23, 25] Indeed, the addition of phenylnitrile oxide to fluoroallene occurs with preferential anti addition for both regioisomenc products (equation 20)... 

Phenyl vinyl sulfones reacted with cyclohexanone enamines 332 to afford adducts which, upon hydrolysis, gave 2-(2-phenylsulfonyl)alkylcyclohexanone 333a . However, in the reaction with phenyl styryl sulfone, two products 333b and 334 were obtained by the nucleophilic attack at the and a-carbon atoms . Steric effects, electrostatic interactions between the nitrogen atom of the enamine and the oxygen atoms of the sulfone group, and medium effects contribute to the regioselectivity of the reaction. ... 

Figure 7-2. Properties of CAII active site in the COHH state (zinc-bound hydroxide and protonated His 64). (a) Superposition of a few key residues from two stochastic boundary SCC-DFTB/MM simulations with the X-ray structure [87] (colored based on atom-types) the two sets of simulations did not have any cut-off for the electrostatic interactions between SCC-DFTB and MM atoms but used different treatments for the electrostatic interactions among MM atoms group-based extended electrostatics (in yellow) and atom-based force-shift cut-off (in green). Extended electrostatics simulations sampled configurations with the protonated His 64 too close to the zinc moiety while force-shift simulations consistently sampled the out configuration of His 64 in multiple trajectories, (b) Statistics for productive water-bridges (only from two and four shown here) between the zinc bound water and His 64 with different electrostatics protocols...

The IPA system does not require a co-solvent, but one can be used if this proves advantageous. In the TEAF system a solvent is normally used, though neat TEAF or formic acid can be used if required. The solvent can have a large effect on the reaction rate and optical purity of the product this may in part be because the substrate seems to bind by weak electrostatic interactions with the catalyst, and is also partly due to the pH of the system. Solvents have a dramatic effect on the ionization of formic acid for example, in water the piCa is 3.7, but in DMF it is 11.5. This is because formation of the formate anion becomes less favorable with less polar solvents (see Table 35.2). The piCa of triethy-lamine is far less sensitive. As a consequence, formic acid and triethylamine may remain unreacted and not form a salt. The variation in formic acid piCa can also have a significant impact on the catalyst and substrate, particularly when this is an imine. 

Under these conditions, the formation rate constant, k, can be estimated from the product of the outer sphere stability constant, Kos, and the water loss rate constant, h2o, (equation (28) Table 2). The outer sphere stability constant can be estimated from the free energy of electrostatic interaction between M(H20)q+ and L and the ionic strength of the medium [5,164,172,173]. Consequently, Kos does not depend on the chemical nature of the ligand. A similar mechanism will also apply to a coordination complex with polydentate ligands, if the rate-limiting step is the formation of the first metal-ligand bond [5]. Values for the dissociation rate constants, k, are usually estimated from the thermodynamic equilibrium constant, using calculated values of kf ... 

Suitable collectors can render hydrophilic minerals such as silicas or hydroxides hydrophobic. An ideal collector is a substance that attaches with the help of a functional group to the solid (mineral) surface often by ligand exchange or electrostatic interaction, and exposes hydrophobic groups toward the water. Thus, amphi-patic substances (see Chapter 4.5), such as alkyl compounds with C to C18 chains are widely used with carboxylates, or amine polar heads. Surfactants that form hemicelles on the surface are also suitable. For sulfide minerals mercaptanes, monothiocarbonates and dithiophosphates are used as collectors. Xanthates or their oxidation products, dixanthogen (R - O - C - S -)2 are used as collectors for... 

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