Localized electrical effects

The magnitude of the localized electrical effect in the case of the substituted ethylenes is the same as that of the substituted acetylenes. The latter are significantly more susceptible to resonance effects than are the former, however. 

As only the localized electrical effect and a possible steric effect need be considered in this data set, the AH values for the alcohols were correlated with equation 26 ... 

In Eq. 71, Q is the quantity to be correlated, and is a parameter which represents the localized electrical effect. 

L and C are equivalent to each other insofar as the magnitude of the localized electrical effect is concerned1. The L values obtained in the correlations are the same for a given M, as they are all less than two standard deviations from each other. The mean values of L for Si, Ge and Sn are 4.46( 0.392), 5.90( 0.459) and 7.88( 0.846), respectively. Although only one L value is available for Pb, it seems that L increases with the atomic number for group 14 elements other than carbon. 

The range of the data encompassed more than 17 orders of magnitude in this set. The value of Pp shows that the localized electrical effect is predominant. The value of t] shows that the electronic demand is comparable to that observed for the ionization of 4-substituted phenols. The statistics reported above are described in the Glossary. In view of the many different original sources of the data and the enormous range of structural type, the goodness of fit is quite reasonable. 

Ti The localized (field and/or inductive) electrical-effect parameter. It is identical to Ci. Though other localized electrical-effect parameters such as a and Op have been proposed, there is no advantage to their use. The a parameter has sometimes been used as a localized electrical-effect parameter such use is generally incorrect. 

C. Definition of Localized Electrical Effect Substituent Constants.131... 

The major disadvantages of the a constants are due to their definition as the difference between two processes, one involving both the localized electrical effect and steric effects, and the other involving only steric effects. The first disadvantage is that the assumption that = ho may be in error. The second is that two experimental measurements are necessary for the determination of each a constant. An additional disadvantage is that a values are not on the same scale as and Op values. 

It is obviously desirable in view of the large number of substituent constants that have been proposed as measures of the localized electrical effect try to bring some order into the confusion which dominates this area. This is of particular importance to the many workers in other fields who would like to make use of linear free energy relationships in their own work and are overwhelmed by the morass of different constants that have been proposed. 

It cannot be overemphasized that the aj constants in Table 8 were defined for use in protonic media. To further establish their validity we have correlated ionization constants for various rigid systems which are free of steric and conformation effects, and are dependent only on the localized electrical effect. The sets studied include 18, 22-26, 29-40,45, 48, and 49 (Table 8). The results of the correlations are set forth in Table 9. They are excellent and confirm the validity of the cr/ constants in Table 7. We have also examined a number of systems, in which the substituent is bonded to an sp hybridized carbon atom which is in turn bonded to one or more sp carbon atoms with excellent results (Sets 19, 20, 27, 28 Table 8). Results of the correlations are in Table 9. These results, coupled with those obtained for substituted acetic acids, show that a... 

We believe that these results show that the ffj constants given in Table 7 constitute the best available parameters for the localized electrical effect at the present time. 

SO2—, etc., and Ak varies also have constant a/ values (See Table 7). These observations support the conclusion that the localized electrical effect of alkyl groups, in solution at least, is in fact constant. 

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