Strictly what is the main reason behind ortho effect?please explain with proper example.

Dear Anurag,

The ortho effect if based on the premise that an ortho-substituted acid (take benzoic acid as an example) is more acidic than the meta or para-substituted form. This effect is not dependent on the nature of the substituent (e- donating or e- withdrawing). The reason for this is that the steric hinderance between the substituent and the neighboring carboxylate forces the carboxylate to bend out of the plane of the aromatic ring. This conformational shift alters the delocalization of the charge into the benzene ring, making it easier for the negative charge to be delocalized throughout the pi-system.

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In very simple words ortho effect arises due to stearic hindrance between groups at adjacent positions of benzene ring which easily removes H+ and hence increases acidity of compound.
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Ortho effect due to a combination of stericAnd electronic factor.Ortho effect is mainly due to sterric hyndrense effect.

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Ortho effect in benzoic acid is the result of strric hinderance at ortho position...Whenever a group , either electron withdrawing or electron pumping, feels steric repulsion due to the bulky carboxylic group. As aresult one of the group, generally the carboxylic group is diverted away from the plane of the ring which make carboxylic acid even more acidic.Exception... if both the ortho positions are substituted by electron rich species the ortho effect os suppressed and the compound is actually less acidic than mono ortho substituted benzoic acid

Is there any exception in the sense that ortho effect is applicable for huge and bulky compounds like CH3 and not with smaller compounds like F , OH ,etc...