IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry - tell me about resonance, inductive effect, hyperconjugation

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Inductive effect - effect of electronegativity, transmitted through intermediate sigma bonds. For example, chloroacetic acid is stronger than acetic acid, because the electron pulling effect of Cl stabilises the accumulation of negative charge on the anion.

Mesomeric effect - effect of resonance, transmitted through conjugated bonds. For example, the OH group of a phenol is strongly activating and ortho, para - directing towards electrophilic substitution in a benzene ring because of the interaction between oxygen lone pairs and the ring; you can write valence structures with a double bond between O and C, a positive charge on O, and a negative charge on the ortho or para ring carbon.

Hyperconjugation - this is a suggested special kind of mesomeric effect, involving for example hydrogen atoms on the -CH3 group of toluene, and suggested contributions from valence structures in which one of these H is H+, and again there is a double bond between the carbon of the CH3 group and the ring, and a negative charge distributed over ortho and para ring carbons. This was suggested to explain the fact that -CH3 is more strongly activating than -C(CH3)3 towards electrophilic attack.

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