Dual Substituent Parameters analysis

Kuokkanen evaluated a series of constants. Kpeg for substituted diazonium ions with PEG 1000 and found a reaction constant (p = 1.12) comparable to those for complexation with the three crown ethers investigated by Nakazumi et al. (1983), p = 1.18-1.38). It is therefore likely that the host-guest interaction of diazonium ions with acyclic polyethers is basically similar to that with crown ethers. A dual substituent parameter analysis (DSP, see Sec. 8.3) for (Nakazumi et al., 1987)... 

For meta- and para-substituted phenols, log values spread over 2 log units from 3-dimethylaminophenol to 4-nitro-3-trifluoromethylphenol. Their order is well explained by classical electronic effects. A dual-substituent parameter analysis gives equations 16 and 17, where crp and ctr are the Taft field-inductive and resonance substituent constants, respectively. 

More accurate information on k3 is obtainable if the equilibrium constant K is also determined at various crown ether concentrations, as shown by Nakazumi et al. (1981, 1983). The results with benzenediazonium tetrafluoroborate and 3- and 4-substituted derivatives demonstrate that k3 is not unmeasurably small, but that ky-values are generally 1-2% of k2 for complexation with 18-crown-6, 0.1-0.5% of k2 with 21-crown-7, and 2-10% of k2 with dicyclohexano-24-crown-8. A dual substituent parameter (DSP) analysis of A 3-values (Nakazumi et al., 1987) showed that the dediazoniation mechanism of the complexed diazonium ions does not differ appreciably from that of the free diazonium ions. 

A Generalized Treatment of Substituent Effects in Benzene Series. A Statistical Analysis by the Dual Substituent Parameter Equation. By S. Eh REN SON, Department of Chemistry, Brookhaven National Laboratory, Upton, Long Island, New York R. T. C. BROWNLEE, Department of Chemistry, La Trobe University, Bundorra, Victoria, Australia R. W. Taet, Department of Chemistry, University of California, Irvine, California. I... 

A Generalized Treatment of Substituent Effects in the Benzene Series. A Statistical Analysis by the Dual Substituent Parameter Equation (1)... 

The previous analysis by the dual substituent parameter equation of substituent effects in the naphthalene series provided support for the scale, especially for sets involving nonconjugating positions (2p). The available data yield six basis sets which presumably give a critical analysis and, in particular, provide distinctions between conjugative (three sets) and nonconjugative positions (three sets). The results (using the earlier symbolism (2p)) are given in Table X. 

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. 

Hammett, L. P. Physical Organic Chemistry. McGraw-Hill New York (1940). Ehrenson, S., Brownlee, R. T. C., and Taft, R. W. Generalized treatment of substituent effects in the benzene series. A statistical analysis by the dual substituent parameter equation (1). Progr. Phys. Org. Chem 10, 1-80 (1973). 

The Hammett-type correlation for the rate constants of 5-allyl-5-R-barbiturates has been reported by Carstensen et al. and suggested for use in stability predictions.569 Similar correlations were also found for the hydrolysis of 5-arylidenebarbituric acids.363,567 Linear free energy relationships have also been reported for dissociation constants,45,51 polarographic half-wave potentials,570 fluorescence70 and luminescence phenomena,71 and 13C-NMR chemical shifts129 for different classes of barbituric acid derivatives. Application of the dual substituent parameters method in LFER analysis of barbiturates, using Taft s polar and steric constants for various chemical and physicochemical properties, was also evaluated.571... 

Attempts were made to apply Hammett benzoic acid-based Om and ap constants to the correlation analysis of spectroscopic data. Some significant correlations were obtained, but many of the correlations were rather poor, trends rather than precise relationships. Success in this area was found to involve the separation of inductive and resonance effects and the application of the dual substituent-parameter (DSP) equation (Section II.B). Indeed the development of the DSP equation became closely connected with the correlation analysis of NMR shielding of substituted fluorobenzenes at an early stage, around I957IO6 0 appijg(j extensively to F NMR data , and within a few years... 

The various dual-substituent-parameter equations can usually improve the correlation of data which give poor correlation with the single-parameter Hammett equation. It must be recognized that in part this is a direct consequence of the introduction of additional parameters. To derive solid mechanistic insight on the basis of such improved correlation requires a critical appraisal of the results and statistical analysis may be required. The details of critical statistical evaluation of free energy correlations have been extensively discussed but this topic is beyond the scope of our coverage. 

From comparisons of the single-substituent parameter equations for the two nitropyridine series 61 and 62, the transmission of the total electronic effects of 6(2)-substituents to the para position were concluded to be higher than that for 5-substituents (73AC(R)135). The analysis of dual-substituent... 

A DSP analysis, in which contributions due to inductive and resonance effects of substituents are considered separately, has been applied in order to obtain a deeper level of insight into the electronic factors influencing pyridinium ion acidities. It has been said that a ... single parameter treatment has the merit of simplicity but where this suggests correlations which are unrealistic in terms of chemical experience, then a dual parameter approach is necessary. 53 The correlation has the form of Eq. (8). While only one set of inductive-effect... 

For correlation analysis, the Y-T equation can be applied directly by least-squares analysis of the dual parameter relationship. However, improvement of the correlation is not of much interest since the increased number of parameters in the Y-T equation should inevitably improve the precision. Particularly in the investigation of reaction mechanisms, insufficient improvement could be more important for indicating the involvement of mechanistic complexity. The correlation will be frequently modified by various extraneous factors. We therefore illustrate the behaviour of substituent effects in several typical benzylic solvolyses in terms of the Y-T relationship. 

Swain-Lupton equation A dual-parameter approach to the correlation analysis of substituent effects, which involves a field constant (F) and a resonance constant (R). The original treatment was modified later. The procedure has been considerably applied, but also much criticized. 

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