Electronic Effects of 5-Substituents

The quatemization of 5-alkylthiazoles with methyl iodide in nitrobenzene has been studied (254) results are summarized in Table III-54. 

The effect of alkyl groups in the 5-position on the reactivity of the thiazole nitrogen is analogous to that found for 3-alkylpyridines, in other words, a simple inductive effect. In passing from the unsubstituted heterocycle to the methyl derivative, the rate constant doubles a further increase in substitution produces a much less pronounced variation. 

The application of the Taft equation, derived from the Hammett equation (262) 

TABLE ra-54. RATE AND ACTIVATION CONSTANTS FOR THE REACTION OF 5-ALKYLTHlAZOLES WITH METHYL IODIDE IN NITROBENZENE. (254). 

TABLE m-55. VERIFICATION OF THE TAFT EQUATION FOR THE KINETICS OF OUATERNIZATION OF 5-ALKYLTHIAZOLES (254) 

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TT-Electron densities, correlation with proton chemical shift, of alkylthiazoles, 344 of phenylthiazoles, 345 Electronic charges, of thiazole, 31 of aminothiazoles, 44 of chlorothiazoles, 44 of methylthiazoles, 40 Electronic effects, of 5-substituents on quaternization, 390 Electronic paramagnetic resonance, 84 coupling constants for nitrothiazoles, 84 coupling constants for 2-thiazolyl radical, 84... 

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