Swain-Lupton parameters

Table 15 contains the C chemical shifts of some selected indazoles. The major difference between indazoles and isoindazoles lies in the chemical shifts of carbons C-3 and C-7a. The substituent chemical shifW (SCS) induced by the substituent in position 3 have been discussed using an empirical model (770MR(9)716). The model that gives the best results, AS = OS + + c and 3i are the Swain-Lupton parameters and 5 is the Schaefer... 

Yukawa and Tsuno have still another approach, also involving dual parameters Yukawa Tsuno Bull. Chem. Soc. Jpn. 1959, 32. 971. For a review and critique of this method see Shorter, in Chapman Shorter. Ref. 18. pp. 119-173, pp. 126-144. This article also discusses the Swain-Lupton and Taft oh cr approaches. For yet other approaches,... 

Correlations between substituent-induced chemical shift differences and reactivity parameters have been examined. Good linear correlations have been obtained using the Swain-Lupton two-parameter equation ... 

Hansch-Leo hydrophobic substituent parameter Hammett sigma constants Modified Swain Lupton constants... 

To characterize the substituents (the X block) a set common substituent parameters were compiled from the literature. These parameters were as (Taft inductive parameter), trp (Hammett parameter for para substituents), F and R (Swain-Lupton dual substituent parameters), Es and Esc (Taft steric parameters), van der Waals radius, L, Bv B2, B3, (Verloop sterimol parameters), MR (molar refractivity), and n (Hansch lipophilicity parameter). Data are given in Refs. [1,19] and are not reproduced here. 

MR molar refractivity it hydrophobic substituent constant and Op overall electronic constants for meta- and para-position K and p Swain-Lupton resonance and field constants L Sterimol length parameter B1 and B5 Sterimol B parameters SD Dash-Behera steric density parameter. 

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. 

Figure 16. The AD values of the meta-substituted triplet diradicals 10 versus the Swain Lupton resonance parameter R.

The Swain-Lupton treatment was a reaction against the proliferation of scales of polar substituent constants. The authors maintained that the polar effect of any given substituent could be adequately expressed in terms of just two basic characteristics a field constant and a fixed resonance constant Swain and Lupton maintained that the correlation analysis of chemical reactivity data and spectroscopic data of aromatic systems could be carried out satisfactorily in terms of and 9. cf the four cri -type parameters introduced for the DSP equation), meta and para series being dealt with separately, as in the case of the DSP equation. The assumptions involved in establishing the and 9 . scales provoked much criticism. Nevertheless, the treatment achieved fair success when applied to chemical reactivity data and some spectroscopic data, particularly The most... 

The n.m.r. spectra of a number of coumarins have been correlated with Hammett constants and with Swain-Lupton and Schaefer parameters. 

The successful decomposition of a values into field and resonance components could eliminate the need for several sets of o values. The Swain-Lupton system must treat meta- and para-substituted compounds as separate reaction series, with differing values for r and / for a meta versus para placement of the substituent. The reason is that resonance interactions are usually stronger in the para series. There must also be an additional parameter for each reaction, since the relative sensitivity to resonance and field effects differs from reaction to reaction. Swain and Lupton have observed satisfactory correlation for over forty reaction series using and This treatment also provides an indication of the relative importance of resonance and field interactions. The mathematical manipulations are, of course, more complex than in the simple Hammett equation. The Swain-Lupton correlations are carried out by a computer program that provides a best-fit correlation in terms of /, r, and The computation also yields percent resonance by comparing the magnitude of/ andr. 

It should be recognized that all of the approaches to linear free-energy relationships have been developed on an empirical basis. The reaction constants, substituent constants, and other parameters involved are specified by the definitions of the correlation equation. The data are then treated by the equation, and the variable parameters arise from the best fit to the correlation equation. In the case of the Hammett equation, each reaction series gives rise to its characteristic p value. For the Swain-Lupton equation, the meta series and the para series would each give rise to / and r. 

An Example of a Change in Mechanism in a Solvolysis Reaction Studied Using cr" 452 A Swain-Lupton Correlation for Tungsten-Bipyridine-Catalyzed Allylic Alkylation 453 Using Taft Parameters to Understand the Structures of Cobaloximes Vitamin 612 Mimics 455 The Use of the Schleyer Method to Determine the Extent of Nucleophilic Assistance in the Solvolysis of Aryl vinyl Tosylates 459... 

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