The atoms or group of atoms are classified based on the Inductive effect as electron-withdrawing (-I) or electron-donating (+I) relative to Hydrogen.
The common functional groups showing +I and -I effect are:
+I group | -I group |
|---|---|
O- | OH, OR, OAr, Ar |
COO- | COOH, COOR |
CH3, CHR2, CH2R, CR3 | NO2, CN |
D | NH2, NH3+, NR3+ |
| F, Cl, Br, I, CF3 |
| SH, SR, SR2+, SO2R, SO2Ar |
| C_=CR, CH=CR2 |
| CHO, COR |
Functional groups with strongest -I effect
The order of -I effect of some common functional groups in the decreasing order to Hydrogen are:
-NH3+> -NO2> -CN> -SO3H> -CHO> -CO-> -COOH> -COCl> -CONH2> -F> -Cl> -Br> -I> -OH> -OR> -NH2> -C6H5> -H
The positively charged ammonium ion and nitro groups have the strongest -I effect when part of a molecule.
Functional groups with strongest +I effect
The order of +I effect of some functional groups in the decreasing order to Hydrogen are:
-O-> -COO-> R3C- > R2CH-> RCH2-> CH3-> D-> H-
The negatively charged hydroxy and carboxylate anions followed by the tertiary alkyl groups show the strongest +I effect when part of a molecule.
This excerpt is from the chapter Electronic Displacements in a Covalent Bond, part of CurlyArrows' Introductory Organic Chemistry Course. Preview the Book.
Related Reading: Inductive effect
