The Inductive Effect refers to the phenomenon wherein a permanent dipole is created in a given molecule due to the uneven distribution of bonding electrons in the molecule. This effect is seen in σ bonds, while the Electromeric Effect can only be seen in π bonds.

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Table of Contents

Inductive Effect on Acidity and Basicity

Types of Inductive Effect

Inductive Effects on the Stability of Molecules

Applications of Inductive Effect

Difference between Electromeric and Inductive Effect

How to Check the Acidity of Compounds?

The Inductive Effect is a type of chemical effect in which the electron density around an atom or a group of atoms is affected by the presence of nearby atoms or groups of atoms.

The introduction of an electron-releasing or an electron-withdrawing species to a chain of atoms (generally a carbon chain) causes a permanent dipole to arise in the molecule. This is referred to as the inductive effect, and is caused by the relay of the corresponding negative or positive charge through the carbon chain by the atoms belonging to it.

![Inductive Effect image 1]()

An illustration of the inductive effect that arises in a chloroethane molecule due to the more electronegative chlorine atom is provided above.

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Introduction to Organic Chemistry

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Lassaigne’s Test

Victor Meyer’s Method

Inductive Effect on Acidity and Basicity

It may be generalised that the electron-withdrawing groups (EWG) increase the acidity of a compound, while electron-donating groups (EDG) decrease the acidity of a compound. This prediction of acidity and basicity of compounds can be made using the inductive effect. Acidity of a compound can be further understood with the help of this concept.

The conjugate base of an acid, RCOO⁻, can be stabilised if R is electron-withdrawing due to delocalisation of the negative charge formed.

If R had been electron-donating, then the conjugate base would be destabilized due to inter-electronic repulsions.

It can be concluded that +I groups decrease the acidity (or increase the basicity) and -I groups increase the acidity (or decrease the basicity) of compounds.

For example, formic acid (HCOOH) is more acidic than acetic acid (CH3COOH) due to the +I inductive effect of the methyl group attached to the carboxylic acid group.

![Inductive Effect 3]()

Note: If the pKa of an acid is high, it is said to be a weak acid ([pKa = -log(Ka)]), but if the Ka of an acid is high, it is a strong acid. The same logic applies to bases.

Consider the acidity of monochloroacetic acid, dichloroacetic acid, and trichloroacetic acid.

It can be said that the presence of three Cl atoms makes oxygen highly electron deficient, polarising the O-H bond the most. Thus, the acidity order for the above compounds is III > II > I.

Types of Inductive Effect

Negative Inductive Effect (or -I Effect)

Positive Inductive Effect: +I Effect

Negative Inductive Effect

When an electronegative atom, such as a halogen, is introduced to a chain of atoms (generally carbon atoms), the electron sharing becomes unequal, resulting in a positive charge being transmitted through the chain.

The formation of a permanent dipole in a molecule due to the electron-withdrawing inductive effect, or the -I effect, results in the electronegative atom holding a negative charge.

Positive Inductive 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 Positive Inductive Effect or the +I Effect.

The Influence of Induction on the Stability of Molecules

The charge on a given atom and the charge on a group bonded to the atom play a strong role in determining the stability of the resulting molecule, as per the inductive effect.

The I-effect can be observed when a group is bonded to a positively charged atom, resulting in an amplified positive charge that decreases the molecule’s stability.

When a negatively charged atom is introduced to a group displaying a -I effect, the charge disparity is reduced and the resulting molecule is stabilized due to the inductive effect.

Furthermore,

When a group displaying the I effect is bonded to a molecule, the electron density of the resulting molecule decreases, making it more likely to accept electrons and thereby increasing the acidity of the molecule.

When a positively charged 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.

Applications of Inductive Effect

Illustration 1:

What is the stability of the following canonical forms?

I and III have more covalent bonds and are more stable than II and IV. Of the two, I is more stable due to its negative charge being on an electronegative element.

Between II and IV, II is more stable due to the same rationale mentioned above.

1. I
2. III
3. II
4. IV

Illustration 2:

We know that EWG increases acidity and EDG decreases acidity.

I group is a Me group whereas R group is an OMe group, so R group decreases the acidity more strongly than Me group.

Therefore, the order is d > c > e > a > b

a → t, b → p, c → s, d → q, e → r

Illustration 3:

The most acidic proton of the substrate will react with NaNH2, forming a conjugate base. This reaction is based on the concept of finding the most acidic proton.

There are totally four protons: -COOH, -OH, nitro-substituted –OH, and alkyne proton.

Since two moles of the base are used, two moles of protons would react.

The order of acidity of protons is

-COOH → -OH (Nitro substituted) → -OH → Acetylenic Proton

So the product would be,

Illustration 4: The order of acidity of the following compounds, from most acidic to least acidic, is

Solution: To determine the acidity of the compounds, remove the proton and assess the stability of the resulting conjugate base.

The intramolecular hydrogen bonding stabilises the conformations of structures I and II, with I being more stabilised than II.

The meta isomer would be more acidic than the para isomer due to the electron-withdrawing effect of the oxygen atom.

Therefore, the order is: I > II > III > IV

Illustration 5:

The most basic among the four is I, as structures II and IV are aromatic. Between I and III, I is more basic due to the presence of an oxygen atom in III, which decreases basicity through the -I effect.

Between II and IV, II would be more basic because in IV, the lone pair on nitrogen is delocalised to make the compound aromatic. This delocalisation of the lone pair prevents it from being available for donation, making IV the least basic.

Therefore, the order is IV < II < III < I.

Inductive Effect vs Electromeric Effect

A tabular column comparing the key differences between the electronic 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 electronic effect is temporary |

| It requires an electrophilic attacking reagent | An electrophilic attacking reagent is necessary for this effect to occur. |

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.

How to Test the Acidity of Organic and Unsaturated Compounds?

To check the acidity of an organic compound, remove the proton and then check the stability of the resulting conjugate base so formed. More the stability of the conjugate base, stronger is the acid.

To check for acidity among unsaturated compounds, check the hybridisation of the carbon involved. The higher the s-character on the carbon, the greater its electronegativity and therefore, the greater its acidity.

Therefore, the order of acidity from most acidic to least acidic is: Alkynes > Alkenes > Alkanes

Preference is given to resonance over induction when two groups compete to withdraw electrons, as resonance affects the entire molecule rather than just the immediate environment.