Groups electron-donating

As expected, the formation of a carbonyl group is not possible with tert-allylic alcohols. Although the aromatic ring bears electron-donating groups, the 2,2-disubstituted chromene 119 was formed smoothly with the tert-allylic alcohol 118[100]. 

The phenylacetic acid derivative 469 is produced by the carbonylation of the aromatic aldehyde 468 having electron-donating groups[jl26]. The reaction proceeds at 110 C under 50-100 atm of CO with the catalytic system Pd-Ph3P-HCl. The reaction is explained by the successive dicarbonylation of the benzylic chlorides 470 and 471 formed in situ by the addition of HCl to aldehyde to form the malonate 472, followed by decarboxylation. As supporting evidence, mandelic acid is converted into phenylacetic acid under the same reaction conditions[327]. 

The meso carbon atom should present a carbenium structure with a low TT electron density in the ground state, in the excited state this carbon possesses the carbeniate structure (C ) with a high tt electron density (119). An electron-donating group in such a position should stabilize the ground state and rise the excited state to the highest level hypsochromic shift results as a whole. 

The electronic influence of the 4-substituent corresponds to a relative increase in the kinetic acidity of the C-5 proton when an electron-withdrawing group (R=Ph) is situated at the 4-position and to a relative increase in the kinetic acidity of the 2-methyl group when an electron-donating group (R = Me) is at the same position (Table 1-59). 

A tertiary carbonium ion is more stable than a secondary carbonium ion, which is in turn more stable than a primary carbonium ion. Therefore, the alkylation of ben2ene with isobutylene is much easier than is alkylation with ethylene. The reactivity of substituted aromatics for electrophilic substitution is affected by the inductive and resonance effects of a substituent. An electron-donating group, such as the hydroxyl and methyl groups, activates the alkylation and an electron-withdrawing group, such as chloride, deactivates it. 

The 3-, 4-, 5- and 6-positions in the pyridazine nucleus are electron deficient due to the negative mesomeric effect of the nitrogen atoms. Therefore, electrophilic substitution in pyridazines is difficult even in the presence of one or two electron-donating groups. The first reported example is nitration of 4-amino-3,6-dimethoxypyridazine to yield the corresponding 5-nitro derivative. Nitration of 3-methoxy-5-methylpyridazine gives the 6-nitro-,... 

When hydroxypteridines are considered, it must be borne in mind that these compounds exist principally in the pteridinone forms, containing thermodynamically stable amide functions, and consequently have low reactivity. Their stability towards acid and alkali correlates well with the number of electron-donating groups which apparently redress the deficit of ir-electrons located at the ring nitrogen atoms. Quantitative correlations can be seen in the decomposition studies of various pteridinones (Table 7). These results are consistent with the number of the oxy functions and their site at the pteridine nucleus. The... 

From UV studies of 4-phenyl-, 4-nitro- and 4-nitroso-pyrazoles, Habraken et al. (67RTC1249,72JHC939) conclude that the 4-pyrazolyl group acts as an electron-donating group. UV spectra of pairs of 1-aryl- and 2-aryl-indazoles and their utility in the determination of isomeric structures are discussed in (67BSF2619) many other UV data on indazole derivatives can be found in (71PMH(3)67). 

The stabilizing role of other functional groups can also be described in resonance terms. Both electron-attracting groups such as carbonyl and cyano and electron-donating groups such as methoxy and dimethylamino have a stabilizing etfect on a radical intermediate at an adjacent carbon. The resonance structures which depict these interactions indicate delocalization of the unpaired electron onto the adjacent substituents ... 

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