Substituent Effect on Acidity, Slides of Organic Chemistry

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SUBSTITUENTSUBSTITUENT

EFFECT ONEFFECT ON

ACIDITYACIDITY

Name School

Substituents that stabilizes the carboxylate anionSubstituents that stabilizes the carboxylate anion relative to undissociated carboxylic acid will driverelative to undissociated carboxylic acid will drive the equilibrium toward increased dissociation andthe equilibrium toward increased dissociation and result in increased acidity.result in increased acidity.

Substituent effects on acidity are also found in substitutedSubstituent effects on acidity are also found in substituted benzoic acids. Thebenzoic acids. The substituents on the aromatic ring stronglysubstituents on the aromatic ring strongly affect reactivity. Aromatic rings with electron-donatingaffect reactivity. Aromatic rings with electron-donating groups are activated toward further electrophilic substitution,groups are activated toward further electrophilic substitution, and aromatic rings with electron-withdrawing groups areand aromatic rings with electron-withdrawing groups are deactivated. Exactly the same effects can be observed on thedeactivated. Exactly the same effects can be observed on the acidity of substituted benzoic acids.acidity of substituted benzoic acids.

As the table shows, an electron- donating (activating) group such as methoxy decreases acidity by destabilizing the carboxylate anion, and an electron-withdrawing (deactivating) group such as nitro increases acidity by stabilizing the carboxylate anion.

ASSESSMENTASSESSMENT

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