Equilibrium constant for formation

Table 3. Equilibrium Constants for Formation of Cyanohydrins from Hydrogen Cyanide Plus Carbonyl Compounds ...

The equilibrium constants for addition of alcohols to carbonyl compounds to give hemiacetals or hemiketals show the same response to structural features as the hydration reaction. Equilibrium constants for addition of metiianoHb acetaldehyde in both water and chloroform solution are near 0.8 A/ . The comparable value for addition of water is about 0.02 The overall equilibrium constant for formation of the dimethyl acetal of... 

The other C=N systems included in Scheme 8.2 are more stable to aqueous hydrolysis than are the imines. For many of these compounds, the equilibrium constants for formation are high, even in aqueous solution. The additional stability can be attributed to the participation of the atom adjacent to the nitrogen in delocalized bonding. This resonance interaction tends to increase electron density at the sp carbon and reduces its reactivity toward nucleophiles. 

From transition state theory, we know that the equilibrium constant for formation of the transition state (FC ) is related to the free energy by the relationship... 

The equilibrium constants for formation of the various complexes should be identical after the experimental values are corrected for the differences in probability for their formation. Also, the stability of the last complex as reflected by Km should be independent of the fact that some of the intermediate... 

In the case of a bidentate ligand the ratio KMLJKWL)i has units of concentration in mol 1 1. If one assumes that the equilibrium constants for formation of the monoco-ordinated complexes ML and ML L are equal,2 combination of the equilibrium constants for (26) and (27) shows that the ratio... 

Although suggested to operate by a mechanism analogous to Scheme 14, the case of the catalysis by the mononuclear complex Fe(CO)5 was proposed to be more limited.86,88 Relative to the Ru catalyst, the equilibrium constant for formation of the metallocarboxylic acid adduct, Fe(C0)4(C02H)-, was found to be several orders... 

The equilibrium constant for formation of activated complex (K ) is given by... 

Let AT be the true thermodynamic equilibrium constant for formation of the transition-state species T from the reactant-state species R and let k be the experimental rate constant for the reaction of R. Neglecting activity coefficients ... 

Equilibrium constants for formation of complexes [Fe(CN)5L] can be derived from kinetics and independently from spectroscopic determinations. Values are given in many of the papers cited above stability constants for several pentacyanoferrate(II) complexes have been compared with those for their pentacyanoruthenate(II) analogues. " ... 

Table 10 Kinetic parameters and equilibrium constants for formation and dissociation of ternary nitric oxide complexes (in water, at 298 K). 

Equilibrium constants for formation of iron(III) complexes of several oxoanions, of phosphorus, arsenic, sulfur, and selenium, have been reported. The kinetics and mechanism of complex formation in the iron(III)-phosphate system in the presence of a large excess of iron(III) involve the formation of a tetranuclear complex, proposed to be [Fc4(P04)(0H)2(H20)i6]. The high stability of iron(III)-phosphate complexes has prompted suggestions that iron-containing mixed hydroxide or hydroxy-carbonate formulations be tested for treatment of hyperphosphatemia. " ... 

The acid-catalysed reaction 66 The hydroxide-ion catalysed reaction 74 Spontaneous or water-catalysed reaction 80 Formation of oxocarbocations equilibrium constants for formation of hemiorthoesters 84... 

The Hammett p-value for cleavage of the exocyclic bond of 2-methoxy-2-substituted-phenyl-l,3-dioxolans (—1.58 + 0.06) is a little larger than that for cleavage of the endocyclic C— bond of 2-hydroxy-2-substituted-phenyl-l,3-dioxolans (—1.24 + 0.04) (Table 9) (Chiang et al., 1983). A direct comparison between the p-values for C—OMe bond cleavage of trimethyl orthobenzoates and dimethyl hemiorthobenzoates is not possible at present since they have not been measured in the same solvent. However, that based on H+ for the breakdown of the hemiorthobenzoates (— 1.58) is less than that based on the equilibrium constants for their conversion into methyl benzoates and methanol which is —1.9 (derived from the equilibrium constants for formation of the hemiorthobenzoates, McClelland and Patel, 1981b). This implies that the development of positive charge in the transition state is less than in the final product, the ester. 

FORMATION OF OXOCARBOCATIONS EQUILIBRIUM CONSTANTS FOR FORMATION OF HEMIORTHOESTERS... 

The kinetic effects of C02 in the base catalyzed hydrolysis of some carboxylato amine cobalt(III) complexes have been reported (80-82). In the base catalyzed hydrolysis of oxalatopentaammine-cobalt(III) (80), C02 retarded the reaction due to the formation of a virtually unreactive ion-pair, f (N H .) r, 2 2 COi ]. The equilibrium constant for formation of carbonate ion-pairs with (glycinato-O) (tetraethylene-pentamine)cobalt(III), (81) and (o-methoxybenzoato) (tetraethylenepentamine)cobalt(III) (82) were, however, much smaller than for the oxalatopentamminecobat(III) and a very weak rate retardation and virtually no effect was observed in the base catalyzed hydrolysis of the latter two complexes. 

Table 19 Equilibrium Constants for Formation of Mono-fi-diketone Complexes of V02+ in Aqueous Solution at 25 °C...

EDTA (ethylenediaminetetraacetic acid) (H02CCH2)2NCH2CH2N-(CH2C02H)2, the most widely used reagent for complexometric titrations. It forms 1 1 complexes with virtually all cations with a charge of 2 or more, effective formation constant Equilibrium constant for formation of a complex under a particular stated set of conditions, such as pH, ionic strength, and concentration of auxiliary complexing species. Also called conditional formation constant. 

Transition state inhibitors. Suppose that a chemical reaction of a compound S takes place with rate constant /cx through transition state T. Let the equilibrium constant for formation of T be Kj-. Assume that an enzyme E can combine either with S with dissociation constant Kds or with the compound in its transition state structure T with dissociation constant Kdj (Eq. 9-83). 

The title olefins form complexes with Ni(0) with equilibrium constants for formation decreasing in the order ethylene > styrene > propylene 1-hexene > disubstituted alkenes (28). With ethylene and styrene the (olefin)NiL2 complexes have been isolated with L = P(0-o-tolyl)3. Addition of HCN to solutions of the pure olefin complexes results in rapid and complete conversion to alkylnickel cyanide intermediates which are spectroscopically detectable subsequent C—C coupling gives the observed nitrile products propionitrile from ethylene and (predominantly) 2-phenylpropion-itrile from styrene (47). The same alkyl intermediates are formed when ethylene and styrene are added to HNiL3CN [L = p(0-o-tolyl)3]. 

The formation of a complex ion is a stepwise process, and each step has its own characteristic equilibrium constant. For formation of Ag(NH3)2+, the reactions are... 

The stability of a complex ion is measured by its formation constant Kf (or stability constant), the equilibrium constant for formation of the complex ion from the hydrated metal cation. The large value of Kf for Ag(NH3)2+ means that this complex ion is quite stable, and nearly all the Ag+ ion in an aqueous ammonia solution is therefore present in the form of Ag(NH3)2+ (see Worked Example 16.12). 

A similar procedure to the above may also be carried out for brominolyses by bromine in the presence of bromide ion some values of the equilibrium constant for formation of Br3 are given in Table 2. 

It is of interest to examine the general case when a nucleofuge is displaced from a carbonyl group by a nucleophile with a labile hydrogen, HNu, which becomes much more acidic upon formation of the tetrahedral intermediate (Scheme 11.10). Catalysis by the general base B will be observed when the intermediate 4 breaks down to reactants faster than it transfers a proton to water. The rate constant for formation of 5, which may or may not represent the overall rate constant of reaction, is given by kn [B] K, where K is the equilibrium constant for formation of 4 and kK is the rate constant of proton transfer from 4 to the catalyst B. 

---