Question

What are various types of groups?? like +I, -I, +M, -M, +R, -R.

Also please state the decreasing order of their reactivities.

Answer 1

+I= elrctron donating groups. e.g. -CH3
-I= electron withdrawing groups e.g. -Cl
+M= Mesomeric effect, groups which push electron away from itself by delocalisation of pi bond in aliphatic compounds.
-M= Mesomeric effect,groups which pulls electron towards itself by delocalistion of pi electron in aliphatic compounds.
+R = resonance effect, which push electron away from itself by delocalisation of pi bond in aromatic compounds.
-R= resonance effect, groups which pulls electron towards itself by delocalistion of pi electron in aromatic compounds.
Resonance effect>Mesomeric effect>Inductive effect(I)