Dual substituent parameter approach

For cyclohexane rrans-fused hydrazone analogs of 37 (R1 = H, R2 = Ar, R3 = Me, CH2Ph), the presence of only the open-chain form was observed. The C = N 13C-chemical shifts of hydrazones were analyzed for the first time in terms of separate resonance and inductive effects by using the dual-substituent-parameter approach (94JOC5895). 

Earlier sections of this chapter contain accounts of the Yukawa-Tsuno equation85,86, the Dual Substituent-Parameter (DSP) equation91,92 and Extended Hammett (EH) equation95 (see Section II.B), with the particular intention of showing how these may be applied to data sets involving the substituents of particular interest for this chapter. These equations are not now the only possibilities for multiparameter treatment. In this section we shall give accounts of some of the other approaches. The accounts will necessarily be brief, but key references will be given, with indications as to how the substituents of interest for this chapter fit into the various treatments. 

Effects of single, isolated substituents on physical properties, reactions, or equilibria can be treated successfully on the basis of dual substituent parameter (DSP) approaches. To deal with di- or poly-substituted systems is less straightforward. Here the question arises of how individual substituents combine their respective actions. It is in this context that the captodative substituent effect has to be seen. 

Substituent effects on the acidity of pyridinium ions46,47 have been extensively studied in order to learn about the ability of a hetero-aromatic ring to transmit electronic effects and to determine how and to what extent substituents influence the protonation of an annular nitrogen atom. No other series of heteroaromatic compounds has been studied as carefully and as thoroughly as these model compounds. Yet, interpretations are far from being universally accepted. Single-parameter Hammett treatments will be considered before dual-substituent parameter (DSP) approaches. 

Conjugation of the nitrogen lone pair with the adjacent phosphoryl or carbonyl function was tested by the 13C NMR parameters of the N-phosphorylated and N-acetylated aniline, as well as of their complexes with Lewis acids. (h ). The inductive and resonance constants for the neutral and charged amide groups were determined using the dual substituent parameter (dsp) approach. ( 5). Results are given in the Table. 

More insights into the substituent effects which are responsible for the generation of helix optical rotations of cyclopropanes I can be obtained through a dual substituent parameter (DSP) approach Referring to the polar substituent constant (which... 

Though satisfying from a numerical point of view, correlation (35) disregards an essential physical effect associated with the constitutional isomerism in allenes and must be subjected to a criticism which has been given in connection with Equation 8. Any numerical improvement of the preceding correlation (35) using instead of a single-parameter approach a dual-substituent parameter (DSP) approach (2,4) also buries these physical problems. 

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... 

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. 

A comprehensive treatment of the dual parameter approach was given by Ehrenson, S. Brownlee, R. T. C. Taft, R. W. Prog. Phys. Org. Chem. 1973, 10, 1. See also the treatment of substituent effects in nonaromatic unsaturated systems by Charton, M. Prog. Phys. Org. Chem. 1973,10,81. 

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