The mesomeric effect is negative (-M) when the substituent is an electron-withdrawing group, and the effect is positive (+M) when the substituent is an electron releasing group. But at some places it is written +M of OR is less (which is correct). +M EFFECT ORDER Resonance Effect or Mesomeric effect In Chemistry. M or R symbols are used to represent the resonance effect. It is defined as the polarity produced in the molecule by the interaction of two pi bonds or between a pi bond and lone pair of electrons present on an adjacent atom. The mesomeric effect in chemistry is a property of substituents or functional groups in a chemical compound. But I am not able to understand the reason which they give. -M EFFECT ORDER : –NO2 > –CN > --S(=O)2−OH > –CHO > –C=O > –COOCOR > –COOR > –COOH > –CONH2 > –COO− What is the way to understand such comparisons ? In some books it is written that +M (mesomeric effect) effect of OH is less than that of OR . The withdrawal effect or releasing effect of electrons attributed to a particular substituent through the delocalization of π or pi-electrons that can be seen by drawing various canonical structures is called resonance effect or mesomeric effect. The Meaning of Ramanujan and His Lost Notebook - Duration: 1:20:20. Also, why is an -OR group weaker than the -NH2 group ?

Why does the -OH group show stronger mesomeric effect than the -NH2 group ? View 37 Upvoters s CiR p zRHe o b n lD s ka o MaOd r vkM e CQf d XGBoN XylY b vHh y p cfo B sVfw H uDAe M i D rtzmd GeJGQ D dJWop e CeiEM r qz m FljH a sKcgk l N
Center for Advanced Study, University of Illinois at Urbana-Champaign Recommended for you . The withdrawal effect or releasing effect of electrons attributed to a particular substituent through the delocalization of π or pi-electrons that can be seen by drawing various canonical structures is called a resonance effect or mesomeric effect.

Resonance Effect Or Mesomeric Effect In Chemistry. The reason they give is inductive effect of R (group) which sounds senseful .