Yukawa-Tsuno equation substitution

Another example of enhanced sensitivity to substituent effects in the gas phase can be seen in a comparison of the gas-phase basicity for a series of substituted acetophenones and methyl benzoates. It was foimd that scnsitivtiy of the free energy to substituent changes was about four times that in solution, as measured by the comparison of A( for each substituent. The gas-phase data for both series were correlated by the Yukawa-Tsuno equation. For both series, the p value was about 12. However, the parameter r" ", which reflects the contribution of extra resonance effects, was greater in the acetophenone series than in the methyl benzoate series. This can be attributed to the substantial resonance stabilization provided by the methoxy group in the esters, which diminishes the extent of conjugation with the substituents. 

Yukawa, Tsuno and their colleagues121 have made studies more specifically related to determining substituent constants, which have included both methylsulfinyl and methylsulfonyl groups. Hydroxyl chemical shifts were determined for a large number of m-and p-substituted phenols in DMF and in DMSO. The results were treated by the LArSR relationship121 (usually called the Yukawa-Tsuno equation, see Section II.B) ... 

It has been shown that Yukawa-Tsuno equation for 4-substituted benzene derivatives is approximately equivalent to the CR equation1819. This has led to the development of a modified Yukawa-Tsuno (MYT) equation which has the form ... 

In considering quantitatively the response of these groups to high electron-demand there are certain caveats. In the first place it must be remembered that amino and related groups are liable to be protonated in the kind of media often used for studying electrophilic aromatic substitution. The observed substituent effect will then be that of the positive pole. Secondly, the straightforward application of the tr+ scale to electron-demanding reactions is not necessarily appropriate. It may well be that some form of multiparameter treatment is needed, perhaps the Yukawa-Tsuno equation (Section II.B). 

The rate of reaction of 2-bromo-3,5-dinitrothiophene (470) with meta and para substituted anilines has been determined (76JOC968). The kinetic data are accommodated by the Ingold-Yukawa-Tsuno equation (1). 

They further suggest the Yukawa-Tsuno equation for substitution should take the form... 

Partial rate factors for trifluoroacetylation at the 5-position of 2-substi-tuted furans in 1,2-dichloroethane at 75°C [Table 6.7, [72JCS(P2)71]] correlate approximately with u+ values, with p = -10. The effects of para substituents on the rate of acetylation and trifluoroacetylation of 2-aryl-5-methylfurans have been studied. In the latter reaction, the relative rates of substitution at the 3-position (to give 6.10) were H, 1.0 Cl, 0.43 Me, 5.3 and OMe, 35.4, which correlated with the Yukawa-Tsuno equation, p = -2.6, r = 0.74. For acetylation, the corresponding relative rates for... 

The rate coefficients for the hydrolyses of substituted methyl orthobenzoates in 70 % methanol—water obey Hammett s rule with p = —2.0 [169]. There are no positive deviations for substituents with electronreleasing resonance effects, and it is not necessary to apply a + values and the Yukawa—Tsuno equation. 

The Yukawa-Tsuno equation continues to find considerable application. 1-Arylethyl bromides react with pyridine in acetonitrile by unimolecular and bimolecular processes.These processes are distinct there is no intermediate mechanism. The SnI rate constants, k, for meta or j ara-substituted 1-arylethyl bromides conform well to the Yukawa-Tsuno equation, with p = — 5.0 and r = 1.15, but the correlation analysis of the 5 n2 rate constants k2 is more complicated. This is attributed to a change in the balance between bond formation and cleavage in the 5 n2 transition state as the substituent is varied. The rate constants of solvolysis in 1 1 (v/v) aqueous ethanol of a-t-butyl-a-neopentylbenzyl and a-t-butyl-a-isopropylbenzyl p-nitrobenzoates at 75 °C follow the Yukawa-Tsuno equation well, with p = —3.37, r = 0.78 and p = —3.09, r — 0.68, respectively. The considerable reduction in r from the value of 1.00 in the defining system for the scale is ascribed to steric inhibition of coplanarity in the transition state. Rates of solvolysis (80% aqueous ethanol, 25 °C) have been measured for 1-(substituted phenyl)-l-phenyl-2,2,2-trifluoroethyl and l,l-bis(substi-tuted phenyl)-2,2,2-trifluoroethyl tosylates. The former substrate shows a bilinear Yukawa-Tsuno plot the latter shows excellent conformity to the Yukawa-Tsuno equation over the whole range of substituents, with p =—8.3/2 and r— 1.19. Substituent effects on solvolysis of 2-aryl-2-(trifluoromethyl)ethyl m-nitrobenzene-sulfonates in acetic acid or in 80% aqueous TFE have been analyzed by the Yukawa-Tsuno equation to give p =—3.12, r = 0.77 (130 °C) and p = —4.22, r — 0.63 (100 °C), respectively. The r values are considered to indicate an enhanced resonance effect, compared with the standard aryl-assisted solvolysis, and this is attributed to the destabilization of the transition state by the electron-withdrawing CF3 group. 

Yukawa-Tsuno equation A multiparameter extension of the Hammett equation to quantify the role of enhanced RESONANCE effects on the reactivity of meta- and para-substituted benzene derivatives, for example,... 

The Yukawa-Tsuno equation r values have been measured for the solvolysis reactions of substituted benzyl cations and a-substituted analogs. HF/6-31G charges and bond orders have been calculated for the presumed cationic intermediates. Analyze the data for relationships between r and the structural parameters. 

Rate constants for the protodetriethylgermylation of 3- or 4-substituted phenyltriethyl-germanes and the protodetricyclohexylstannylation of 3- or 4-substituted phenyltricy-clohexylstannanes were correlated with the modified Yukawa-Tsuno (MYT) equation (equation 17) to give the regression equations ... 

Rate data for the Menshutkin reaction between strongly activated Z-substituted benzyl / -toluenesulfonates and Y-substituted lV,lV-dimethylanilines in MeCN at 35 °C fit the equation kohs = h +k2 [DMA], which is consistent with concurrent first- and second-order processes.The 5 nI constant ki is unaffected by changing the nucleophile and conforms to Yukawa-Tsuno treatment with p — -5.2 and r — 1.3. The 5 n2 constant k2 was increased by electron-donating substituents in the nucleophile and showed upward curvature when subjected to the Brown a + treatment. 

The Hammett equation traditionally combines 3-substituted and 4-substituted benzene derivatives into a single data set using the composite constants for the former and constants for the latter. This is justifiable only if p3 is equal to P4 (Ap 0). We have shown that this is generally not the case except when the geometry of XGY is comparable to that of the benzoic acids from which the and Op constants were defined. The Yukawa-Tsuno and related equations are based on the assumption that P3 is equal to p4 and are limited to applications in which this is at least approximately correct. They are briefly reviewed elsewhere. ... 

The magnitude of p is in accord with a reaction at a ring C atom. Winkler and Winkler have also reported equilibrium and rate constants (sets CR7 and CR8, Table 9). We described above a modified Yukawa-Tsuno (MYT) equation (equation 6) with a taking the value for 3-substituted benzene derivatives and <750 for 4-substimted benzene derivatives, while for substituents in the meta position is 0. For this application the appropriate value of was unknown and all three pure electrical effect parameters were used for the para substituents thus the MYT equation used was equation 37 ... 

First-order dependence is observed with respect to both the oxidant and reductant in the oxidation of substituted anilines with peroxomonosulfate anion. Addition of acid causes retardation of the reaction. Yukawa-Tsuno correlation of the rates gave a negative reaction constant (p -1.7) and analysis of the effect of solvent in terms of Grunwald-Winstein equation (m 0.4) indicated an S -type reaction. 

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). ... 

The Hammett equation (1) was applied for more than ten years without major difficulty. With the extension of experimental knowledge to new areas and new reactions certain deviations from the relationship were detected. The deficiencies in the scope of the simple two-parameter Hammett expression (1) were recently discussed by van Bekkum and his associates (1959) and Yukawa and Tsuno (1959). Reactions which proceed without the development of important resonance interactions between the substituent and the side-chain adhere to the relationship. On the other hand, deviations are found for reactions such as the solvolysis of substituted phenyldimethyl-carbinyl chlorides which are now recognized to be of a different character... 

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