Question

Can anyone give the list of +R and -R groups or +M and -M groups (Resonance or Mesomeric)?

Answer 1

Answer:

The mesomeric effect in chemistry is a property of substituents or functional groups in a chemical compound. 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.

+M effect of a methoxy group in an ether

–M effect of a carbonyl group in acrolein

The effect is used in a qualitative way and describes the electron withdrawing or releasing properties of substituents based on relevant resonance structures and is symbolized by the letter M. 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 donating group.

+M EFFECT ORDER :

–O− > –NH2 > –OR > –NHCOR > –OCOR > –Ph > –CH3 > –F > –Cl > –Br > –I

-M EFFECT ORDER :

–NO2 > –CN > –SO3H > –CHO > –COR > –COOCOR > –COOR > –COOH > –CONH2 > –COO−