And electron withdrawing

Alkylation of tetrazoles as the anions gives mixtures of 1- and 2-alkyl isomers. In general, electron-donating substituents in the 5-position slightly favor alkylation of the 1-position and electron-withdrawing 5-substituents slightly favor the 2-position. 

The closely related N- arylazoaziridine system (278) decomposes in refluxing benzene to give aryl azides and alkenes, again stereospecifically (70T3245). However, biaryls, arenes and other products typical of homolytic processes are also formed in a competing reaction, although this pathway can be suppressed by the use of a polar solvent and electron withdrawing aryl substituents. 

Since substituents at the triple bond also determine its polarization, the copper acetylides containing both electron-releasing and electron-withdrawing groups were introduced into the reaction of cyclocondensation (78IZV1175 81IZV902). 

For diaroy I peroxides (36, R ar 11. m- and / -electron withdrawing substituents retard the rate of decomposition while m- and/ -clcctron donating and all o-substituents enhance decomposition rates. The o-substiluent effect has been attributed to the sensitivity of homolysis to steric factors. 

This effect is observable within a series of very similar electrophiles. Zollinger27 found that in reactions of diazonium ions substituted with 4-C1, 3-C1, and 3-N02 substituents (i.e. the reactivity and electron-withdrawing power of the ion increased along the series) the respective kinetic isotope effects were 6.55, 5.48 and 4.78. 

Copolymers composed of electron-donating and electron-withdrawing units are considered to have intramolecular charge transfer structure.41 These copolymers show absorption bands at wavelengths longer than those of the corresponding homopolymers (Fig. 9.2). 

All substituents increase reactivity at ortho and para positions over that of benzene. There is no great difference between electron-donating and electron-withdrawing groups. 

In another aspect of the mechanism, the effects of electron-donating and electron-withdrawing substituents (p. 1065) indicate that the diene is behaving as a nucleophile and the dienophile as an electrophile. However, this can be reversed. Perchlorocyclopentadiene reacts better with cyclopentene than with maleic anhydride and not at all with tetracyanoethylene, though the latter is normally the most reactive dienophile known. It is apparent, then, that this diene is the electrophile in its Diels-Alder reactions. Reactions of this type are said to proceed with inverse electron demand ... 

Most carbenes are electrophilic, and, in accord with this, electron-donating substituents on the alkene increase the rate of the reaction, and electron-withdrawing... 

In the reaction with butanone, an equilibrium between the CH3-activated complex and the CH2-activated complex is observed and it is revealed that the former is a thermodynamic product and the latter is a kinetic product. These results indicate that the relative reactivity of the C-H bonds is in the order of 2>1>3, and the large and electron-withdrawing substituents retard the reaction. A plausible mechanism is shown in Scheme 63. When the oxy-... 

Kahn and Hehre stated that the regiochemistry of Diels-Alder reactions of electron-rich dienes and electron-withdrawing dienophiles follows from matching the nucle-ophilicity of the dienes and the electrophilicity of the dienophiles, although it has... 

Contrary to fraras-azoferrocene, the cis form exhibits one-step 2e oxidation waves, and its oxidation potential, E° = 0.03 V in Bu4NC104-benzonitrile, is more negative than that of the trans form (E() = 0.29 and 0.50 V vs. Ag/Ag ) by 0.3 V. These data imply that the 7r-conjugation ability and electron-withdrawing nature of the azo group is retarded in the cis form. 

The effect upon the transphosphorylation reaction with alcohols and amines of electron-releasing (CH3) and electron-withdrawing (Cl, N02) groups in the benzene ring of phosphoric imidazolides has been studied as well.[191]... 

Reference has already been made to electron-donating and electron-withdrawing groups, their effect being to render a site in a molecule electron-rich or electron-deficient, respectively. This will clearly influence the type of reagent with which the compound will most readily react. An electron-rich species such as phenoxide anion (36)... 

The Alper group [163] reported on a highly efficient double carbohydroamination for the preparation of a-amino carboxylic acid amides 6/1-345, starting from aryl iodides and a primary amine 6/1-344, in usually high yield (Scheme 6/1.88) both, aryl iodides with electron-donating and electron-withdrawing groups can be used. 

The influence of substituents on regioselectivity was studied by using a model nitrone 3,4-dihydro-2,2-dimethyl-2/f-pyrrole 1-oxide (DMPO, 256) with different alkylidenecyclopropanes substituted with phenyl (156), electronreleasing (270 and 271) and electron-withdrawing groups (52, 272 and 4) [67,... 

---