Resonance effects electron-withdrawing

Resonance effects Electron donors slow the reaction withdrawers accelerate it. Inductive effects Electron withdrawers accelerate the reaction. 

Phenyl is electron-donating by resonance but electron-withdrawing by induction, so what has happened is that the ortho substituents have forced the COOH out of the plane of the benzene ring so that there is no resonance overlap between the benzene ring and the COOH orbitals. The COOH "feels" the benzene ring as simply an inductive substituent. Resonance has been "inhibited" because of the steric effect of the substituent. ... 

Free radicals can be stabilized by resonance and electron-withdrawing effects. When their stabilization is sufficient—in particular, due to the existence of many canonical forms—they can become persistent and be isolated, like the following free radicals ... 

An a hydrogen of an aide hyde or a ketone is more acidic than most other protons bound to carbon Aldehydes and ketones are weak acids with pK s in the 16 to 20 range Their enhanced acidity IS due to the electron withdrawing effect of the carbon yl group and the resonance stabi lization of the enolate anion... 

Carboxylic acids are weak acids and m the absence of electron attracting substituents have s of approximately 5 Carboxylic acids are much stronger acids than alcohols because of the electron withdrawing power of the carbonyl group (inductive effect) and its ability to delocalize negative charge m the carboxylate anion (resonance effect)... 

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. 

A Hammett plot of the pK values of p-substituted phenols against the Op values shows serious deviations for the members of the series at the extremes of the o scale, that is, for substituents that are strongly electron donating or electron withdrawing. It was recognized very early that such deviations could be rectified by choosing an appropriate o value for such substituents in effect, this means a different model reaction was adopted. The chemical basis of the procedure can be illustrated with the p-nitro substituent. The p-nitrophenolate ion is stabilized by through resonance as shown in 2. 

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