Sun April 17, 2011 By: Ankush Singla

How to find out which effect(inductive(+I,-I),hyperconjugation(+H,-H),mesomeric(+M,-M) is acting on a compound???????? tell me giving some examples that in whicch compound which effect is acting .How stability depends on these effects

Expert Reply
Sun April 17, 2011
Inductive effect - This is basically the 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 - This is the 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 - Hyperconjugation is the stabilising interaction that results from the interaction of the electrons in a sigma-bond (usuallyC-H or C-C ) with an adjacent empty (or partially filled) p-orbital or a pi-orbital to give an extended molecular orbital that increases the stability of the system.
So, basically by examining the compound we can judge about which effect is going to apply.
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