Inductive Effect refers to the phenomenon wherein a permanent dipole arises in a given molecule due to the unequal sharing of the bonding electrons in the molecule. This effect can arise in sigma bonds, whereas the electromeric effect can only arise in pi bonds.
What is the Inductive Effect?
When an electron-releasing or an electron-withdrawing species is introduced to a chain of atoms (generally a carbon chain), the corresponding negative or positive charge is relayed through the carbon chain by the atoms belonging to it. This causes a permanent dipole to arise in the molecule and is referred to as the inductive effect.
An illustration describing the inductive effect that arises in a chloroethane molecule due to the more electronegative chlorine atom is provided above.
The Polarization of Covalent Bonds
It is observed that in the sigma bonds between two different atoms, the electron cloud is always closer to the more electronegative of the two atoms participating in the sigma bond. Due to this, there is a permanent dipole that arises in the bond and the covalent bond is said to be polarized.
An illustration describing the polarity of the covalent bonds in a water molecule is provided above. The more electronegative atom is said to have a partial negative charge and the less electronegative atom has a partial positive charge in the polar covalent bond.
When an electronegative atom, such as a halogen, is introduced to a chain of atoms (generally carbon atoms), the resulting unequal sharing of electrons generates a positive charge which is transmitted through the chain.
This causes a permanent dipole to arise in the molecule wherein the electronegative atom holds a negative charge and the corresponding effect is called the electron withdrawing inductive effect, or the -I effect.
When a chemical species with the tendency to release or donate electrons, such as an alkyl group, is introduced to a carbon chain, the charge is relayed through the chain and this effect is called the +I Effect
Effect on Stability, Acidity, and Basicity of Molecules
The charge on a given atom and the charge on a group bonded to the atom play a strong part when determining the stability of the resulting molecule as per the inductive effect.
An example of this can be observed when a group displaying the -I effect is bonded to a positively charged atom and the positive charge on the resulting molecule is amplified, reducing its stability.
On the other hand, when a negatively charged atom is introduced to a group displaying a -I effect, the charge disparity is somewhat quenched and the resulting molecule would be stable as per the inductive effect.
When a group displaying the -I effect is bonded to a molecule, the electron density of the resulting molecule effectively reduces, making it more likely to accept electrons and thereby increasing the acidity of the molecule.
When a +I group attaches itself to a molecule, there is an increase in the electron density of the molecule. This increases the basicity of the molecule since it is now more capable of donating electrons.
Inductive Effect vs Electromeric Effect
A tabular column highlighting the key differences between the electromeric and the inductive effects can be found below.
|Inductive Effect||Electromeric Effect|
|Works on sigma bonds||Works on pi bonds|
|The inductive effect is permanent||The electromeric effect is a temporary effect|
|It doesn’t require any attacking reagent||An electrophilic attacking reagent is required for this effect to arise.|
Thus, it can be understood that the +I and -I effects play a vital role in the stability as well as the acidity or basicity of molecules.
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