Inductive Effect; Electrophile & Nucleophile - Organic Chemistry

There are some basic principles of organic chemistry that mainly include fission of covalent bonds, types of species based on relative electronegativity strength, and electron displacement effects. Here, we will study all of them but will limit our discussion to the Inductive effect. We will also study other electronic effects in the next article.

Outline of this Course: –

Fission Of A Covalent Bond
Nucleophile And Electrophile
Electron Displacement Effects In Covalent Bonds
Inductive Effect
Mesomeric effect
Resonance Structure
Resonance Effect
Electromeric Effect (E Effect)
Hyperconjugation
Types Of Organic Reactions And Mechanisms
Geometrical isomerism
Isomerism isomerism

Fission of covalent bond:

A covalent bond can undergo fission by two mechanisms:
(1) By Homolytic Fission
(2) By Heterolytic Fission

Homolytic fission: In this process, the covalent bond breaks symmetrically wherein each atom of the bond acquires one of the bonding electrons.

Heterolytic fission: In this process, one atom in the bond acquires both bonding electrons. If A-B is a covalent bond and A is more electronegative then B acquires both bonding electrons. The image below illustrates the mechanism.

Electrophile:

An Electrophile is a positively charged or a neutral species making it electron deficient.
Ex. He^–, H₂0⁺, CH₃, NH₄⁺, AICl₃, S0₃, CHCl₂, CCI₃, etc

Nucleophile:

A Nucleophile is a negatively charged or a neutral species having electrons as a lone pair.
Ex. (HO^–), Cyanide (C = N), H₂0: R₃N, R₂NH, etc

Electron Displacement Effects In Covalent Bonds:

A species or a group may be present of different electronegativity. This causes electronic displacement.
The various effects observed: –
1. Inductive Effect
2. Resonance Effect or Mesomeric Effect
3. Electromeric Effect
4. Hyperconjugation Effect

Inductive Effect:

A covalent bond may contain two species having different electronegativities. This difference causes a shift of electron cloud away from a more electronegative group to a less electronegative group. This is termed the “Inductive Effect”.

As a result, a certain degree of polarity in the bond is introduced.
The more electronegative atom acquires a small negative charge (δ^–). Similarly, the less electronegative atom acquires a small positive charge (δ⁺).

Types of Inductive Effect:

An atom or a group can displace electron cloud towards Carbon. This is called the Positive Inductive effect.
→ +I groups: – O –, – COO –, –CR3, –CHR2, –CH2R, –CH3, –D

It can also pull the electron cloud away from the Carbon. This is called the Negative Inductive effect.
→ -I groups: –NO₂, – SO₂R, –CN, –SO₂Ar, –COOH, –F, – Cl, – Br, – I, –OAr, –COOR, –OR, –COR, –SH, –SR, –OH, –Ar, – CH = CR₂

The effect remains prominent up to 2-3 consecutive carbon atoms.

Inductive Effect Order:

(1) For +I Groups
– O ^–> – COO ^–> –CR₃ > –CHR₂ > –CH₂R > –CH3 > –D

(2) 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

Application of Inductive Effect:

To check the relative acidic strength of carboxylic acids.
To check the relative strength of various organic bases.
For qualitative estimation of dipole moment and bond length.
To check the stability of carbocation, carbanions, and carbon-free radicals.

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