Inductive Effect

Inductive Effect

When a covalent bond is formed between atoms of different electronegativity, the electron density is more towards the more electronegative atom of the bond. Such a shift of electron density results in a polar covalent bond. Bond polarity leads to various electronic effects in organic compounds.

Let us consider cholorethane ($\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Cl}$) in which the C−Cl bond is a polar covalent bond. It is polarised in such a way that the carbon-1 gains some positive charge ($\delta^{+}$) and the chlorine some negative charge (δ^–). The fractional electronic charges on the two atoms in a polar covalent bond are denoted by the symbol $\delta$(delta) and the shift of electron density is shown by an arrow that points from $\delta^{+}$ to $\delta^{-}$ end of the polar bond.

2$\delta$C₂+H₃ 1C+H₂Cl

In turn carbon-1, which has developed partial positive charge (δ⁺) draws some electron density towards it from the adjacent C-C bond. Consequently, some positive charge (δδ⁺) develops on carbon-2 also, where δδ⁺ symbolises relatively smaller positive charge as compared to that on carbon – 1.

In other words, the polar C – Cl bond induces polarity in the adjacent bonds. Such polarisation of σ- bond caused by the polarisation of adjacent σ-bond is referred to as the inductive effect. This effect is passed on to the subsequent bonds also but the effect decreases rapidly as the number of intervening bonds increases and becomes vanishingly small after three bonds.

The inductive effect is related to the ability of substituent(s) to either withdraw or donate electron density to the attached carbon atom. Based on this ability, the substitutents can be classified as electron-withdrawing or electron-donating groups relative to hydrogen.

(1) Electron Withdrawing Groups: Halogens and many other groups such as nitro(−NO₂), cyano (−CN), carboxy (−COOH), ester (COOR), aryloxy (-OAr, e.g. −OC₆H₅),etc. are electron-withdrawing groups.

(2) Electron Donating Groups: Alkyl groups like methyl (−CH₃) and ethyl (−CH₂−CH₃) are electron-donating groups.

The decreasing -I effect or increasing +I effect order is as follows:

Types of Inductive Effect

Inductive Withdrawal Effect (−I)

An atom or group that is more electronegative than hydrogen like halogens F, Cl, Br, I and nitro groups NO₂. They withdraw electrons from the adjacent carbon atom, creating a partial positive charge.

-I - effect (Negative inductive effect)

Those atoms or groups of atoms having a greater tendency to displace $\sigma$ e-towards itself as compared to the Hydrogen atom is called the Negative Inductive effect

Negative Inductive effect increases the acidity of carboxylic acid

Electron-Donating Effects (+I)

Atoms or groups, which are low-electronegativity and have electron-donating properties, such as alkyl groups. This effect is also called the +I effect.

Application of Inductive Effect

The decreasing -I effect or increasing +I effect order is as follows:

$-\mathrm{NH}_3^{+}>-\mathrm{NO}_2>-\mathrm{SO}_2 \mathrm{R}>-\mathrm{CN}>-\mathrm{SO}_3 \mathrm{H}>-\mathrm{CHO}>-\mathrm{CO}>-\mathrm{COOH}>-\mathrm{F}>-\mathrm{COCl}>-\mathrm{CONH}_2>$$-\mathrm{Cl}>-\mathrm{Br}>-\mathrm{I}>-\mathrm{OR}>-\mathrm{OH}>-\mathrm{NR}_2>-\mathrm{NH}_2>-\mathrm{C}_6 \mathrm{H}_5>-\mathrm{CH}_2=\mathrm{CH}_2>-\mathrm{H}$

Recommended topic video on(Inductive Effect)

Solved Examples Based on Inductive Effect

Question.1 Arrangement of $\left(\mathrm{CH}_3\right)_3 \mathrm{C}-,\left(\mathrm{CH}_3\right)_2 \mathrm{CH},-\mathrm{CH}_3 \mathrm{CH}_2=$ when attached to benzyl or an unsaturated group in increasing order of inductive effect is-

(1)(1) $\left(\mathrm{CH}_3\right)_3 \mathrm{C}-<\left(\mathrm{CH}_3\right)_2 \mathrm{CH}-<\mathrm{CH}_3 \mathrm{CH}_2$
(2) $\mathrm{CH}_3 \mathrm{CH}_2-<\left(\mathrm{CH}_3\right)_2 \mathrm{CH}-<\left(\mathrm{CH}_3\right)_3 \mathrm{C}=$
(3) $\left(\mathrm{CH}_3\right)_2 \mathrm{CH}-<\left(\mathrm{CH}_3\right)_3 \mathrm{C}-<\mathrm{CH}_3 \mathrm{CH}_2=$
(4)$\left(\mathrm{CH}_3\right)_3 \mathrm{C}<\mathrm{CH}_3 \mathrm{CH}_2<\left(\mathrm{CH}_3\right)_2 \mathrm{CH}$

Solution:

As we learned-

Inductive Effect -When a covalent bond is formed between atoms of different electronegativity, the electron density is more towards the more electronegative atom of the bond. Such a shift of electron density results in a polar covalent bond. Bond polarity leads to various electronic effects in organic compounds. Let us consider chloroethane $\left(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Cl}\right)$ in which the C−Cl bond is a polar covalent bond. It is polarised in such a way that carbon-1 gains some positive charge (δ⁺) and the chlorine has some negative charge (δ^–).

The fractional electronic charges on the two atoms in a polar covalent bond are denoted by the symbol δ (delta) and the shift of electron density is shown by an arrow that points from δ⁺ to δ^– end of the polar bond. In turn, carbon-1, which has developed a partial positive charge (δ⁺) draws some electron density towards it from the adjacent C-C bond. Consequently, some positive charge (δδ+) develops on carbon-2 also, where δδ⁺ symbolises a relatively smaller positive charge as compared to that on carbon – 1. In other words, the polar C – Cl bond induces polarity in the adjacent bonds. Such polarization of σ- bond caused by the polarisation of adjacent σ-bond is referred to as the inductive effect.

This effect is passed on to the subsequent bonds also but the effect decreases rapidly as the number of intervening bonds increases and becomes vanishingly small after three bonds. The inductive effect is related to the ability of substituent(s) to either withdraw or donate electron density to the attached carbon atom. Based on this ability, the substituents can be classified as electron-withdrawing or electron-donating groups relative to hydrogen. Electron Withdrawing Groups: Halogens and many other groups such as nitro(−NO₂), cyano (−CN), carboxy (−COOH), ester(COOR), aryloxy (-OAr, e.g. −OC₆H₅), etc. are electron-withdrawing groups. Electron Donating Groups: Alkyl groups like methyl$\left(-\mathrm{CH}_3\right)$ and ethyl $\left(-\mathrm{CH}_2-\mathrm{CH}_3\right)$ are electron-donating groups.

The greater the number of alkyl groups, the greater the inductive effect.–The CH₃ group has a +I effect. As the number of – CH₃ group increases the inductive effect increases. Hence, the order of inductive effect is $\mathrm{CH}_3 \mathrm{CH}_2-<\left(\mathrm{CH}_3\right)_2 \mathrm{CH}-<\left(\mathrm{CH}_3\right)_3 \mathrm{C}=$

Hence, the answer is option (2).

Question.2 Select the correct statement about the Inductive effect?

(1) Inductive effect transfers electrons from one carbon atom to another.

(2) Inductive effect is the polarization of s bond electrons

(3) Inductive effect creates net charge in the molecule.

(4) Inductive effect is distance-dependent

Solution:

As we learned-

When a covalent bond is formed between atoms of different electronegativity, the electron density is more towards the more electronegative atom of the bond. Such a shift of electron density results in a polar covalent bond. Bond polarity leads to various electronic effects in organic compounds.

Let us consider chloroethane($\left(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Cl}\right)$) in which the C−C bond is a polar covalent bond. It is polarised in such a way that carbon-1 gains some positive charge (δ+)and the chlorine has some negative charge (δ^–). The fractional electronic charges on the two atoms in a polar covalent bond are denoted by the symbol δ (delta) and the shift of electron density is shown by an arrow that points fromδ¯+to δ¯ end of the polar bond.

In turn, carbon-1, which has developed a partial positive charge (δ⁺) draws some electron density towards it from the adjacent C-C bond. Consequently, some positive charge (δδ⁺) develops on carbon-2 also, where δδ⁺ symbolizes a relatively smaller positive charge as compared to that on carbon-1.

In other words, the polar C – Cl bond induces polarity in the adjacent bonds. Such polarization of σ- bond caused by the polarisation of adjacent σ-bond is referred to as the inductive effect. This effect is passed on to the subsequent bonds also but the effect decreases rapidly as the number of intervening bonds increases and becomes vanishingly small after three bonds.

The inductive effect is related to the ability of substituent(s) to either withdraw or donate electron density to the attached carbon atom. Based on this ability, the substituents can be classified as electron-withdrawing or electron-donating groups relative to hydrogen.

(1) Electron Withdrawing Groups: Halogens and many other groups such as nitro(−NO₂), cyano (−CN), carboxy (−COOH), ester(COOR), aryloxy (-OAr, e.g. −OC₆H₅),etc. are electron-withdrawing groups.

(2) Electron Donating Groups: Alkyl groups like methyl $\left(-\mathrm{CH}_3\right)$ and ethyl $\left(-\mathrm{CH}_2-\mathrm{CH}_3\right)$ are electron-donating groups

The displacement of $\sigma$ electron towards a more electronegative atom is called the inductive effect.

Inductive Effect is distance-dependent.

Hence, the answer is option (4).

Question.3 Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Order of acidic nature of the following compounds is A > B > C.

Reason R: Fluoro is a stronger electron-withdrawing group than the Chloro group.
In light of the above statements, choose the correct answer from the options given below

1) Both A and R are correct, and R is the correct explanation of A

2) A is false, but R is true

3) Both A and R are correct, but R is NOT the correct explanation of A

4) A is true, but R is false

Solution:

Acidic strength $\alpha$-I effect

$
\alpha \frac{I}{+I}_{\text {effect }}
$

Among A and B, since the inductive effect is distance dependent, the Extent of –I effect is higher in A, followed by B.
even though F is a stronger electron-withdrawing group than Cl. Thus, A is more acidic than B.

Hence, the answer is option (3).

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Conclusion

As the name implies, it refers to the situation in which an unbalanced distribution of bonding electrons occurs in any given molecule, causing a permanent dipole to form in the molecule. The formation of permanent polarisation as a result of the partial displacement of sigma e- along the carbon chain or partial displacement of sigma-bonded electron toward more electronegative atom in the carbon chain (i.e., the magnitude of partial positive charge) is referred to as the sigma effect. The inductive effect is a long-term phenomenon. This effect can occur in both sigma and pi bonds, but the electromeric effect can occur only in sigma bonds and pi bonds. The influence on electron density in a region of a molecule caused by electron-withdrawing or electron-donating groups in other portions of the molecule is referred to as electron density shift.