Grunwald-Winstein Y values

The values of Z and 7 values belong to a class of solvent parameters based on various standard physical processes (electromagnetic transition, dielectric constant, NMR chemical shift, etc.. In the context of similarity these parameters are not directly useful for mechanistic studies because the reference process is a physical property rather than a chemical reaction. The parameters Z and are often linearly related to the Grunwald-Winstein Y value (Figure 14) and provide a secondary definition of Y values which are inaccessible via the chemical definition of those parameters. 

Solvolysis in Aqueous Systems. In weakly acidic hydroxylic solvents, nitrite ion is a better leaving group than acetate ion, and l,li-adducts typically follow an aromatization path that leads to the formation of an aryl acetate and the elements of nitrous acid. Figure 2. Kinetic studies of solvolysis of the adducts derived from hemimellitene reveal the characteristics of El eliminations. Rates of solvolysis of both the cis and trans-isomers can be correlated to measures of solvent ionizing power such as Grunwald-Winstein Y values. Figure if. Both isomers... 

A study of the aquation of the [Co(NH8)5(DMSO)] + ion in mixed aqueous-organic solvents which involves loss of an uncharged ligand does not show any correlation with solvent parameters, including the Grunwald-Winstein Y values, the water activity, or the heats of mixing of DMSO with solvent components. Nevertheless an 7d mechanism is proposed and the activation parameters are AH -23.9 0.7 kcal mol and AS = 0.36 2.29 cal mol. ... 

The material of this chapter is arranged in three sections, on reactions in pure (that is single) solvents, in mixed solvents, and in salt solutions. In each section the discussion covers a variety of solvent properties, including fundamental properties such as dielectric constant and composition, empirical solvent parameters such as Grunwald-Winstein Y and Reichardt t values, and more qualitative, elusive, or nebulous properties such as solvation and solvent structure. The aim is to provide convenient cross-referencing rather than a detailed and critical treatment. In some cases a less cursory mention will be found in Chapters 1—5 of this Part, or in Part II of Volume 2. 

The aquation kinetics of the chloropentaamminecobalt(III) ion in water-ethanol mixtures has been studied. The rate constants correlate well with the Grunwald-Winstein Y parameter and with the dielectric constant of the medium. The data supports a D mechanism for the reaction. The loss of chloride from the complexes cw-[Co(en)2(NH2CH2CH20H)Cl] and cw-[Co(en)2(NH2(CH2)3 0H)Cl] has been studied in aqueous ethyleneglycol at 40-65 °C in acidic media and at 20-35 °C in basic media.The rate constants decreased linearly with the increasing mole fraction of the cosolvent. The loss of chloride resulted in the formation of the chelated amino-alcohols as the main product. The observed solvent isotope effect (A h2oAd2o) = 112 at 50 °C, [HCIO4] =0.01 moldm for chloride release is lower than the value reported for the aquation of the cw-[Co(en)2(alkylamine)Cl] complexes (1.38-1.44). This result may indicate the lack of direct solvent intervention in the act of substitution at the cobalt(III) center, as expected for a true intramolecular reaction. 

The general SPP scale of solvent dipolarity/polarizability and the specific SB and SA scales of solvent HBA basicity and HBD acidity, respectively, are orthogonal to one another and they can be used in the correlation analysis of solvent effects in single- or, in combination with the others, in two- or three-parameter correlation equations, depending on the solvent-influenced process under consideration see also Section 7.7. Examples of the correlation analysis of a variety of other solvent-dependent processes by means of SPP, SB, and SA values, including those used for the introduction of other solvent polarity parameters, can be found in references [335-337, 340-342]. In particular, comparisons with Kamlet and Taft s n scale [340] and Winstein and Grunwald s Y scale [341] have been made. 

For situations where solvent nucleophilicity may be a factor, Kevill (8) favors the use of the extended Grunwald-Winstein equation (equation 1). Scales of NOTs and OTs values based upon the use of methyl tosylate and 2-adamantyl tosylate as model SN2- and SNl-reacting substrates have been developed (15, 16). Also Y scales have been developed for other anionic leaving groups using 1-adamantyl or 2-adamantyl derivatives (17-19), where Sn2 reaction is impossible or severely hindered. 

Examples of Grunwald-Winstein treatments of reactivity trends have become rare in inorganic chemistry. Some more information has been presented on such plots for aquation of [M(NH3)5Br] + cations with M=Cr or Co in aqueous alcohols. The variation of rate constant with solvent Y value for the isomerization of a chlorophenylacetylene complex of platinum to its chloro-phenylalkynyl form, equation (3), is so small that an intramolecular mechanism is indicated. ... 

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