What is ortho effect?

Hi Sreedhar, While all substituents on aryl rings can influence acidity by inductive and mesomeric effects, substituents on the ortho position are special. They can also influence acidity significantly by sterics, forcing the carboxylic acid group to bend out of the plane of the benzene ring. Since conjugation of carboxylic acid to aryl rings is known to increase the its acidity, bending out of the plane causes an acidity decrease. More poorly understood but also thought to be significant is that ortho substituents can inhibit solvation of the carboxylate anion. It is different for acid as well as base. For Acid - Ortho substituted carboxylic acid is strong acid than the benzoic acid, due to steric hindrance effect by Ortho substituent . For Base- Ortho substituted aniline is always weak base than Aniline. All the best.

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