Electrical effect, composition

We shall find it useful to consider three categories of conclusions transmission of electrical effects, composition of electrical effects, and other conclusions. 

We had previously described the composition of the electrical effect by means of E, where... 

We believe that a more useful measure of the composition of the electrical effect may be defined as... 

Values of Pr for the substituent constants commonly used with eq. (1) are given in Table I. When correlations are made with eq. (1), the substituent constant used determines the composition of the electrical effect. 

The composition of the electrical effect in these sets is reported in the form of the p values in Table IV. Most of the sets studied show a value of Pr of 42, which corresponds roughly to that of the Op substituent constants. 

A number of correlations of ionization potentials for substituted benzenes (40-42), benzyl (43), phenoxy (44), and alkyl (45) radicals and substituted pyridines (46) with the simple Hammett equation have been reported. Charton (47) has studied the application of the extended Hammett equation to substituted ethylenes and carbonyl compounds. The sets studied here are reported in Table II (sets 2-10 and 2-11). Results of the correlations are set forth in Table 111. The results obtained are much improved by the exclusion of the values for X = C2 H3, Ac, F, H and OAc from set 2-10 (set 2-lOA) and the value for X = H from set 2-11 (set 2-11 A). The composition of the electrical effect corresponds to that found for the Op constants as is shown by the pR values reported in Table IV. 

Values of are given in Table VII. The value obtained for set 5-1 seems to show that the substituent effect in the vinylidene position is predominantly a localized effect. Further data are necessary to firmly establish the composition of the electrical effect. 

With regard to the composition of the electrical effects, values of pj for the sets studied are reported in Table XIV. The sets in which the hydroxyl group is the reaction site generally exhibit a Pr value of about 39. The cis-3-substituted acrylic acids show a p value of 39 in aqueous solution. The value of 71 obtained in 50% aqueous ethanol seems too large. 

No conclusion can be made with regard to the composition of the electrical effect in this set, as (3 was not significant in the correlation with eq. (2). In conclusion, it would seem that most sets of cis-vinylene data are free of steric effects. 

The composition of the electrical effect in the case of the 1,4-benzo-quinones seems to depend upon the degree of substitution. The association constants and charge transfer absorption energies of the 2-substituted-l,4-benzo-quinone-hexamethylbenzene complexes (sets 15-2 and 154) show values of pj of 55 and 44 respectively. Values of p are set forth in Table XVII. 

Composition of the Electrical Effect-Carbon-Carbon Double-Bond Sets... 

With regard to the composition of the electrical effect, examination of the p values reported in Table XVII shows that in six of the sets which gave significant correlation, the localized effect is predominant (in these sets, either Pr < 50 or / is not significant). Thus it would appear that in so far as substituent effects are concerned, there are two major classes of electrophilic addition to the carbon-carbon double bond predominance of the localized effect or predominance of the delocalized effect. This behavior may well be accounted for in terms of the reaction mechanism. The rate-determining step in the electrophilic addition reaction is believed to be the formation of an intermediate which may be either bridged or a free carbonium ion. 

In so far as the composition of the electrical effect is considered, the values of p given in Table XVll show that for both nucleophilic and electrophilic radicals, the resonance effect seems to predominate, probably in the case of the former and almost certainly in the case of the latter. 

Data are extant in the literature for two other sets of ethynylene compounds. The sets studied are reported in Table XXXIII. Results of correlation are set forth in Table XXXIV and values of Pr in Table XXXV. The ionization constants of 3-substituted propiolic acids, which were first correlated with the Hammett equation by Charton (18), gave an excellent correlation with eq. (2) (set 22-27-1). The results are very much improved by the elimination of the value for X = H (set 33-27-2). The composition of the electrical effect corresponds approximately to that of the Op constants. The magnitude of the electrical effect is significantly less than that observed for the rrans-3-substituted acrylic acids. 

Only one set of data is available in this system, and it has only four points. Although significant correlation is obtained, the results can in no way be considered conclusive. It is fascinating to note that the value of Pr for this set is 46, which corresponds approximately to the Pr value of the Op constants. An explanation for this composition of the electrical effect has been proposed by Charton (19). It is obvious that this system is in need of further investigation. 

Only two sets of cis-cyclopropylene data are extant in the literature, and each set has only four points. It is therefore not surprising that neither set gives a significant correlation with eq. (2). This system is obviously in great need of further study to ascertain the presence or absence of steric effects and the magnitude and composition of the electrical effect. 

The Eo values for 2-substituted 1,4-benzoquinones (sets 45-4 through 45-7, 45-10) show an average value of pr of 59. Thus the resonance effect predominates. For most of these sets, the Op constants are not the best parameters for correlation. By contrast, the electron reduction potentials (set 45-8) show a Pr value of 39, which indicates predominance of the localized effect. The 2,5-disubstituted 1,4-benzoquinones differ distinctly in their behavior from the 2-substituted 1,4-benzoquinones in that they show an average Pr value of 53. The one-electron reduction potentials of these compounds show about the same composition of the electrical effect, with a value of Pr of 50. The only set of Eq values available for the 2,6-disubstituted 1,4-benzoquinones pve a Pr value of 51, comparable to the values observed for the 2,5-disubsti-tuted 1,4-benzoquinones. The 2,3,5,6-tetrasubstituted 1,4-benzoquinones have... 

SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 181 B. Composition of the Electrical Effect... 

From the previous discussion, in which it was pointed out that both a and P must be functions of Y, we see that pR, which is a function of a and p, must also be a function of Y. It will therefore be convenient to compare the composition of the electrical effect transmitted by various groups G with Y and the reaction conditions held constant. Again, the most useful reaction for this purpose is the ionization of carboxylic acids in water at 25°. Not only are there more sets of data available for this reaction than for any other, but the sets studied for this reaction generally include more substituents than do sets for other reactions or under other reaction conditions. 

Mechanistic. QSRR and those QSAR which involve enzyme reactivity can provide information about the sensitivity of a reaction to electrical effects, its electronic demand, the composition of the electrical effect and the sensitivity to steric effects. QSAR which involve binding to receptor sites can provide information about the nature of the receptor site. Other QSAR can shed light on the bioactivity-determining step. 

When the composition of the electrical effect, Pd. is held constant the LDR equation simplifies to the CR equation ... 

When both the electronic demand and the composition of the electrical effect are held constant, a set of composite parameters having the form ... 

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