Transmission of substituent effects

In the second, which belongs to a systematic study of the transmission of substituent effects in heterocyclic systems, Noyce and Forsyth (384-386) showed that for thiazole, as for other simple heterocyclic systems, the rate of solvolysis of substituted hetero-arylethyl chlorides in 80% ethanol could be correlated with a constants of the substituent X only when there is mutual conjugation between X and the reaction center. In the case of thiazole this situation corresponds to l-(2-X-5-thiazolyl)ethyl chlorides (262) and l-(5-X-2-thiazolyl)ethyl chlorides (263). 

IV. Transmission of Substituent Effects through Heterocyclic Systems 236... 

In the manner outlined, a few attempts have been made to apply the Hammett equation to the transmission of substituent effects in the pyridine series. In the alkaline hydrolysis of 5-substituted ethyl picolinates (5-R-2-COOEt) in 85% ethanol at 25, 35, and 45°, the reaction constants are about 60% as large as those in the corresponding benzene series the overall fit to the Hammett equation, however, is at best fair, since out of four points (R = Et, H, I, Ac) one (Ac) deviates widely. 

Reaction Series Involving the Transmission of Substituent Effects Through Heterocyclic Rings... 

The paucity of data for substituted ethynylene sets is remarkable. Before any definitive conclusions concerning the transmission of substituent effects by the triple bond can be made, much further investigation is required. This field is one which is certainly worthy of further inquiry. 

In the application of the extended Hammett equation to the system XGY, where X is a substituent and Y is a reaction site, both of which are attached to the skeletal group G, the question of the degree of transmission of substituent effects through G arises. The transmitivity of G is measured by the magnitude of a and (3. Now,... 

Among the earliest research on the transmission of substituent effects was the pioneering work of Lauterbur (58) and of Spiesecke and Schneider (59). For a wide series of substituted methanes and ethanes they found an approximate correlation of >3C chemical shifts with the electronegativity (E) of the substituents (X). So they concluded that inductive effects through o-bonds play an important role in determining the chemical shifts of a- and -positioned carbon atoms, and that this effect reflects the substituent s electron-withdrawing or -releasing ability. 

For co-oxidation of nuclear-substituted styrenes, Table I shows a consistently decreasing rarh product as the polarity difference increases in pairs of substituted styrenes, the minimum value being about 0.4. This effect cannot be steric and must be polar. The polar effects could be caused by transmission of substituent effects through the O—O link, to some tendency of different styrenes to associate in solution—i.e., actual... 

The rates of sodium borohydride reduction of the ketones (46) in propan-2-ol have been measured (78JCS(P2)1232). The strategy was to vary X keeping Y = H, and then to vary Y with X = H. This permitted direct comparisons to be made of transmission of substituent effects through the aromatic rings to the same reaction centre. It was concluded that the... 

Bowden94 studied the transmission of substituent effects through C=C in the esterification of 3-substituted acrylic acids with diazodiphenylmethane (DDM) and in the ionization of the same acids. The ap values of the substituents were used to characterize their electronic effects for Hammett-type correlations. In esterification with DDM at 30 °C, the p values of the trans acids and the cis acids were 1.682 and 1.772, respectively, in ethanol... 

So far we have not considered the problem of the transmission of substituent effects in organic molecules during hydrogen exchange reactions in liquid ammonia, and have not compared the regularities... 

Perjessy, A., Janda, M., and Boykin, D.W., Transmission of substituent effects in thiophenes infrared and carbon-13 nuclear magnetic resonance studies, J. Org. Chem., 45, 1366, 1980. 

The problem of the application of the Hammett equation to the electronic transmission of substituent effects through five-membered rings has recently been discussed by Jaffe and Jones.279... 

For reactions involving side-chain carbocations, the order of transmission of substituent effects is quite different to the electrophilic substitutions, being furan > pyrrole > thiophene > benzene > tellurophene. 

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