Lewis acid-base, rate

The rate-determinating step in reaction (45) is second order, illustrating that Lewis acid-base interactions are involved in this process. Eqs. (43)-(45) are similar to reactions (36) and (37) since the tin(II) compounds formed are highly associated (tin(II) chloride and tin(II) sulfide can be isolated as pure and large crystals), the equilibrium is shifted to the right side. 

Thermodynamics of complex formation of silver with several ligands such amines,368 hindered pyridine bases,369 nitrogen donor solvents,370 and azoles371 have been carried out. Other studies include the secondary-ion mass spectra of nonvolatile silver complexes,372 the relationship between Lewis acid-base behavior in the gas phase and the aqueous solution,373 or the rates of hydride abstraction from amines via reactions with ground-state Ag+.374... 

The main advantage of as-described heterocycUc single-source precursors compared to Lewis acid-base adducts is, that these don t tend to give MSb whiskers. Unfortunately, their volatility is much lower and the MOCVD process has to be performed under high-vacuum conditions (10 -10 mbar). In addition, the precursor has to be heated up to 130 °C in order to ensure a reasonable precursor hux rate. 

Equation 58 defines the equilibrium between free silene and its Lewis acid-base complex with a nucleophilic solvent. Since the complexed form of the silene can clearly be expected to be relatively unreactive toward nucleophiles compared to the free silene, then the result will be a reduction in the overall rate constant for reaction with a nucleophilic reagent (Nu-H) in a complexing solvent relative to a non-complexing one like hexane. This rate reduction is described quantitatively in equation 59. 

This equation has been used in several correlations of solvent effects on solute properties such as reaction rates and equilibrium constants of solvolyses, energy of electronic transitions, solvent-induced shifts in UV/visible, IR, and NMR spectroscopy, fluorescence lifetimes, and formation constants of hydrogen-bonded and Lewis acid/base complexes [Kamlet et al., 1986b]. 

The catalytic influence of ammonium chloride on the rate of the reaction was discussed by Claisen in his first report19. Since then, numerous catalysts have been introduced to affect rate enhancements of Claisen rearrangements, e.g., Bronsted and Lewis acids, bases or transition metal complexes. The literature concerning catalytic effects in the Claisen rearrangement has been thoroughly covered until 1984 0,122. 

One-step bond-forming reactions of an electrophile with a nucleophile, Lewis acid-base reactions, are among the most common elementary reactions in organic chemistry. An understanding of the factors determining the rates and equilibria of such reactions would constitute an understanding of much of the entire field of organic chemistry. 

Another explanation for the high plateaus following the minima, and one more logical in view of the fact that these plateaus are about equal to the exchange rate exhibited by pure methanol, is the possibility of interaction of a Lewis acid-base t3rpe between the amines and excess nitro compound or oxime. This would explain not only the equivalence in exchange rate at higher concentrations to that of pure methanol, but also the lack of the... 

Most Other studies have led to considerably more complex behavior. The rate data for reaction of 3-methyl-l-phenylbutanone with 5-butyllithium and n-butyllithium in cyclohexane can be fit to a mechanism involving product formation both through a complex of the ketone with alkyllithium aggregate and through reaction with dissociated alkyllithium. Evidence for the initial formation of a complex can be observed in the form of a shift in the carbonyl absorption band in the infrared spectrum. Complex formation presumably involves a Lewis acid-base interaction between the carbonyl oxygen and lithium ions in the alkyllithium cluster. 

The epoxidation reaction works with many alkenes, but it is slow with mono-substituted (terminal) alkenes. Why do terminal alkenes react more slowly with peroxycarboxylic acids The reaction rate (Chapter 7, Section 7.11) of two alkenes can be examined in order to determine if one is a stronger Lewis base. As a rule, the alkene best able to donate electrons should undergo epoxidation faster if the Lewis acid-base analogy is correct. Alkyl groups are electron releasing, and more alkyl substituents on a C=C unit lead to greater electron density in the 7i-bond, which makes that alkene a stronger Lewis base. 

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