Hammett correlation analysis

Cesium fluoroxysulfate in acetonitrile medium at 35 C converts primary alcohols and alkyl and aryl aldehydes into acid fluorides in high yields.i" Hammett correlation analysis of the fluorination of various benzene-substituted aldehydes gives the reactivity constant31 q = —0.38. It has been shown that solvent polarity plays an extremely important role in the conversion of aldehydes into fluorides the conversion is almost quantitative in acetonitrile, but completely stopped in dichloromethane, hexane or tetrahydrofuran. The presence of ni-... 

For substituted alcohols reacting with hydroxyl radicals, the least substituted alcohol, methanol, was used as a reference compound for Hammett correlation analysis. The o values were taken from Hansch et al. (1995) and rate constants were taken from the U.S. Department of Commerce (USDOC, 1977). These values are believed to be the most accurate rate constants in... 

A few examples have been reported in which no steric parameter is involved in the correlation analysis of cyclodextrin catalysis. Straub and Bender 108) showed that the maximal catalytic rate constant, k2, for the (5-cyclodextrin-catalyzed decarboxylation of substituted phenylcyanoacetic acid anions (J) is correlated simply by the Hammett a parameter. 

Leffler, J. E. Grunwald, E. Rates and Equilibria of Organic Reactions, Wiley, New York, 1963. Hammett, L. P. Physical Organic Chemistry, Reaction Rates, Equilibria, and Mechanisms, 2nd Ed., McGraw-Hill, New York, 1970. Shorter, J. Correlation Analysis on Organic Chemistry, Clarendon Press, Oxford, 1973. Johnson, C. R. The Hammett Equation, Cambridge University Press, New York, 1979. 

The most fruitful treatment of the electronic effects of ozt/zo-substituents involves the use of the same cr/ and correlation analysis for meta- and para-substituents by means of the dual substituent-parameter equation 91 or the extended Hammett equation 95 (Section II.B). Obviously it is a considerable assumption that these are valid for ort/zo-substituents and the implication is that in the correlation analysis any peculiarities may be adequately expressed through the coefficients of the inductive and resonance terms. Really satisfactory correlation analysis for any given reaction system requires a large amount of data and can only rarely be accomplished. 

Some further light on the behaviour of the nitro group as an orf/ o-subsliUicnl in affecting the strength of benzoic acid can be obtained by correlation analysis employing the extended Hammett equation (Section n.B) in the form of equation 14 ... 

The correlation analysis employed the extended Hammett equation in the form of equation 17 ... 

This has been developed since 1986. The title letters stand for Localized Delocalized Response. The localized effect is Charton s preferred name for the inductive effect and delocalized effect is his preferred name for the resonance effect. Indeed, he would like to change the usual symbols from <7/ to 0/, and or to op for the purposes of the Extended Hammett (EH or LD) equation109. The response referred to is that of the substituent to the electronic demand of the site (i.e. reaction site in the correlation analysis of reactivity). Thus this equation, like the PSP equation, is concerned with the parametrization of substituent polarizability. 

Applications of Linear Free Energy Relationships to Polycyclic Arenes and to Heterocyclic Compounds , M. Charton, in Recent Advances in Correlation Analysis in Chemistry , ed. N. B. Chapman and J. Shorter, Plenum, New York, 1978, pp. 175-268. Applications of the Hammett Equation to Heterocyclic Compounds P. Tomasik and C. D. 

When a second nitrogen atom is introduced into the pyridine ring the basicity is reduced (pjRTa 5.23 for pyridine and 2.33 for pyridazine). The effect of the additional substituents on pKK depends on the position of the substituents (Table 3). An extensive set of pK values of pyridazine derivatives has been submitted to correlation analysis using the Hammett and the two Taft equations, which shows that the pKa values are most sensitive to the effect of a 2-substituent followed by the effects of 3- and 4-substituents. The interactions between nitrogen atom and 2-substituents represent over 70% of the inductive character. The composition of the effects of +M 4-substituents is significantly enriched in the resonance interactions, whereas -M 4-substituents interact with the nitrogen atom mainly by induction (77MI21201). 

Correlation Analysis by the Hammett Equation and other LFERs. 319... 

Hammett correlations were developed from experimental data for substituted phenols studied under the UV/Ti02 process (D Oliviera et al., 1993). The mechanism for this reaction is understood to proceed via the hydroxyl radical. Experimental data from the study of dichlorophenols and trichlo-rophenols under UV/Ti02 were used for QSAR analysis (D Oliviera et al., 1993). Figure 9.13 demonstrates the QSAR model for substituted phenols formulated from experimental data. The QSAR model developed for substituted phenols shows a goodness of fit of 0.9766. A good correlation was also established for substituted phenols using Hammett s constant, o the correlation coefficient is 0.987 (D Oliviera et al., 1993). Similar correlation coefficients for the constants o and ores demonstrate that the descriptor ores can be used to accurately predict kinetic rate constants for substituted phenols. 

Shorter, J. 1978. Multiparameter extensions of the Hammett equation. In N.B. Chapman and J. Shorter, Eds., Chapter 4, pp 119-174. Correlation Analysis in Chemistry, Plenum Press, New York. 

Systematic studies of the effects of structure on the biological activities of organic compounds and the analysis of the results are comprised in the term Quantitative Structure-Activity Relationships (QSAR). Many of the treatments employed in the correlation analysis of data in this field closely resemble those used for linear free-energy relationships, e.g. the Hammett equation and extensions thereof, and so the study of the biological properties of organic compounds is often regarded as a part of physical organic chemistry. In recent years, some historical study of work in... 

Hansch constant — A measure of the capability of a solute for hydrophobic (lipophilic) interaction (see - hydrophobic effect) based on the partition coefficient, P, for distribution of the solute between octan-l-ol and water. The most general way of applying P in correlation analysis, etc. is as logP, but the behavior of substituted benzene derivatives maybe quantified by a substituent constant scale, n, which is defined in a way analogous to the Hammett a scale. There are various n scales, depending on the substrate series used as reference. See also - hy-drophilicity. 

Donors and acceptors in ID it systems. Both the structure of the bridge and the strength of donor and acceptor groups decide on the extent of coupling. These strengths may be conveniently defined in terms of the Hammett cr values of classical correlation analysis, which have been split also into electrostatic , resonance and even more contributions (Charton, 1987). Especially suitable for NLO are obviously the resonance constants... 

The effect of substituents on the benzenoid ring on the tautomerism of quinoxaline cations has been investigated using a Hammett correlation and statistical analysis. ... 

The Hammett-Taft analysis of the redox potentials gave a good correlation using parameters. Also, the dependence was additive for the disubstituted ferrocenes,... 

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