In this article, you are going to learn about the inductive effect, including definition, examples, order, and applications.
What is the Inductive Effect?
In a covalent σ-bond between two atoms of dissimilar electronegativity, the more electronegative atom drags the bonding electron pair toward itself due to its greater affinity for electrons. As a consequence, a partial negative charge (δ–) develops on the more electronegative atom and a partial positive charge (δ+) is originated from the other. Thus, the covalent bond can be polarized due to the unequal sharing of the bonding electron, leading to a permanent dipole in a bond. This permanent state of bond polarization is referred to as the inductive effect. The inductive effect is usually shown by the symbol (–>–), where the arrow is always pointed toward the more electronegative atom.
In a long-chain compound, the inductive effect is relayed from one atom to the next, but the effect quickly falls off and becomes negligible. Thus, in a long-chain carbon compound, if the terminal carbon atom is linked up with an electronegative halogen atom (electronic-withdrawing group), then the positive charge is relayed along the carbon chain, and the inductive effect may be represented as in the following diagram,
Similarly, when an electron-donating group or atom is attached to the terminal carbon atom of a carbon chain, the negative charge is relayed along the carbon chain, and the inductive effect may be represented in the following diagram,
Types of Inductive Effect
+I Effect
When an atom or group donates electrons towards the bond and acquires a partial positive charge, the atom or group is called +I group, and the corresponding effect is called the positive Inductive Effect or the +I effect.
Example of +I groups: – O –, – COO –, –CR3, –CHR2, –CH2R, –CH3, –D
-I effect
When an atom or group attracts the bonding electrons towards itself and acquires a partial negative charge, the atom or group is called -I group and the corresponding effect is called the electron-withdrawing inductive effect, or the -I effect.
Example of -I groups: –NO2, – SO2R, –CN, –SO2Ar, –COOH, –F, – Cl, – Br, – I, –OAr, –COOR, –OR, –COR, –SH, –SR, –OH, –Ar, – CH = CR2
Inductive Effect Order
The following groups are listed approximately in order of decreasing strength for both – I and + I effects.
Inductive Effect Order for +I Groups
– O –> – COO –> –CR3 > –CHR2 > –CH2R > –CH3 > –D
Inductive Effect Order for -I Groups
-NR3+ > -SR2+ > -NH3+ > –NO2 > – SO2R > –CN > –SO2Ar > –COOH > –F > – Cl > – Br > – I > –OAr > –COOR > –OR > –COR > –SH > –SR > –OH > –Ar > – CH = CR2
Applications of Inductive Effect
The inductive effect affects some important following properties of organic compounds and these are maybe….
- Acidic strength of aliphatic carboxylic acids.
- The relative strength of organic bases.
- The effect on dipole moment and bond length.
- Stability of alkyl carbocation, carbanions, and carbon-free radicals.