Electron-withdrawing groups decrease

Indolization of the p-substituted phenylhydrazone 45 provides only one regioisomer as expected, the 5-substituted indole 46. It is the most useful example of Fischer indole chemistry. An electron donating substituent on the phenyl ring in 45 enhances the rate of the indolization, whereas electron-withdrawing groups decrease the rate of cyclization. 

For substituted benzenes, ring activators (electron-releasing groups) increase sensitivity and ring deactivators (electron-withdrawing groups) decrease sensitivity (exception halogenated benzenes)... 

Electron-withdrawing groups decrease the rate of the fluoro Pummerer reaction, which, in certain cases,7 allows a DAST-mediated deoxygenation to compete with the introduction of fluorine alpha to sulfur. The reaction is compatible with a number of functional groups and can readily be carried out with nucleosides. Robins and coworkers4 reported the synthesis of a 5 -fluoro-5 -S-phenyladenosine analog using antimony trichloride as catalyst at room temperature. It should be noted that a-fluoro sulfoxides provide a convenient entry to terminal fluoroalkenes.3 8 9 10... 

T2473>. The reaction time for completion of the reaction was found to be dependent on the nature of the substituent in the aryl group. Thus, strongly electron-withdrawing groups decreased the required reaction time (Equation 23). 

Thermolysis of 2-thenoyl peroxide in various solvents indicated that the 2-thenoyloxy radical was sufficiently stable towards decarboxylation, and was trapped as such by the substrates (73IJS295). There was very little indication of the production of 2-thienyl radicals. The kinetics of decomposition of a number of substituted 2-thenoyl peroxides and t-butyl 2-perthenoates have been investigated electron-releasing substituents increase the rate of decomposition, while electron-withdrawing groups decrease the rate. 3-Thenoyl peroxide, on the other hand, seems to provide 3-thienyl radicals on decomposition. Low yields of arylation products like (342) were obtained. 

The ratio of cis/trans reported, is to be strongly influenced by two factors the position of oxygen on acyl chloride precursor and the electronic nature of substituents R1 and R2 on the imine. Thus, the reaction of 2-tetrahydrofuroyl chloride with imine is more stereoselective than that of 3-tetrahydrofuroyl chloride. The presence of electron withdrawing group decreases the stereoselectivity of reaction while the presence of electron releasing group on imine increases stereoselectivity. 

Purine has a pK value of 2.39. Thus, the molecule is more basic than pyrimidine (pK = 1.31), but less basic than imidazole (6.99). Electron-withdrawing groups decrease, electron-donating groups increase basicity. Hydroxy and sulfanyl groups which form oxo or thioxo tautomers weaken the acidic properties. The pK values shown in Tables 3-5 were determined spectropho-tometrically, potentiometrically, by NMR, etc (cf. also Table 15, p 320 ff). 

Most carbenes are electrophilic, and, in accord with this, electron-donating substituents on the alkene increase the rate of the reaction, and electron-withdrawing groups decrease it, although the range of relative rates is not very great. As discussed on p. 284, carbenes in the singlet state (which is the most common state) react stereospecifically and syn, probably by a one-step mechanism, similar... 

Electron-withdrawing groups decrease the availability of the non-bonding electron pair and decrease basicity amides are much less basic than ammonia. 

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