Swain-Lupton treatment

The Swain-Lupton, Taft and Dewar-Grisdale equations all require that the substituent in the reaction under investigation remains at the same position relative to the reaction centre. Thus meta and para series have to be treated separately unlike the Yukawa-Tsuno method where both meta and para substituents may be taken together. The Swain-Lupton treatment may be illustrated by the reaction of chloride ion with substituted benzenediazonium chlorides (Figure 7, Equation 26). ... 

Swain advanced Equation (34) analogous to that in the Swain-Lupton treatment of polar effects (Equation 21). 

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... 

These began with a paper by Swain and Lupton in 1968. The approach was slightly modified and greatly extended by Hansch s group in 1973. During the first 15 years or so of its life, the Swain-Lupton treatment was applied extensively, but was also severely criticized. A revised version appeared in 1983 in a paper by Swain and coworkers ". This version was in its turn severely criticized, but also applied. The Swain-Lupton treatment was reviewed by the present author in 1978 and again more briefly in 1982. A more recent review covers also the revised version and an account of a mini-symposium in print in which several of Swain s critics set forth their views, and Swain replied . 

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. 

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. 

Analogous DSP treatments, but with differences with regard to the basis of the calculations, were proposed by Charton (1981) and by Swain s group (Swain and Lupton, 1968 Swain et al., 1983). The potential significance of polarizability effects resulted in a triple substituent parameter treatment (Taft, 1983). A slightly different... 

Swain and Lupton (2q) have recently presented a modified form of the dual substituent parameter treatment. In this treatment, the p/parameters were... 

Table IV lists comparative SD and / values for fittings of all of the reactions of Table II and III with each of the gr scales derived in this paper. The comparison includes figures for fittings with F and R values of Swain and Lupton (S L) and fitting with the Hammett equation. We believe the results given in Table IV provide a clear confirmation of the uniqueness and limited generality of the o/2(ba) scale. Very consistently, the fit achieved by the or (BA) scale is shown in Table IV to be superior by significant factors to that achieved by any of the other scales or by the simple op treatment. This fact is clearly reflected in the overall / values and the similarly weighted root-mean-square / values, F = y/lfnif lN, sum taken over all reactions. The value of F is. 067 for the basis sets of Table II (compare with overall / of. 058). The comparable F values are. 140 for Or, . 088 for S L, and. 155 for 0(p) with the data differences as explained in Table IV. For all sets of Table IV, the corresponding figures are. 073 for o (ba). -143 for a%, . 097 for S L, and. 209 for 0(py...

Another approach to the treatment of the variability of resonance and field effects was devised by Swain and Lupton. Their approach is to partition substituent effects into pure resonance and field contributions. The substituent constant would then be expressed as a sum of the field and resonance contributions. 

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