Inductive effect applications

 

Negative Inductive Effect (-I Effect):

   - When an *electron-withdrawing group (EWG)* is attached to a carbon chain, it pulls electron density away from the chain. This leads to a decrease in electron density along the chain.

   - Example: ( C - C ^δ+++ -- C ^δ++ -- C ^δ+-- A ^δ-) 

     - Here, A is an electron-withdrawing group, causing a partial positive charge buildup on the adjacent carbons as electron density is pulled towards A.

 *-I Effect Order:* 

*Halogens:* 

- F > Cl > Br > I 

- -I effect → increases with electronegativity. 

Order of -I Effect (Decreasing order of strength): 

-NF₃ > -NR₃⁺ > -NH₃⁺ > -NO₂ > -C≡N > -CHO > -COOH > - F > Cl > Br > I 

*Positive Inductive Effect (+I Effect)*:

   - When an *electron-donating group (EDG)* is attached to a carbon chain, it pushes electron density towards the chain, increasing electron density.

   - Example: \( C - C ^δ--- - C ^δ-- - C ^δ- - B ^δ+ \) 

     - In this case, B is an electron-donating group, pushing electrons towards the carbon chain, leading to partial negative charge on adjacent carbons.

+I Effect Order

- *Reversible order:* 

- Electronegativity (EN) ↓ → +I Effect ↑ 

  F < Cl < Br < I (Good +I effect) 

*Electron Donating Groups (EDGs):* 

CH₂⁻ > NH⁻ > COO⁻ 

3° > 2° > 1°

*Applications of inductive effect:* 

1. Stability of Intermediates

Stability of intermediates is based on the complexity of the molecular structure. It not only discuss stabilty of intermediate but also talks about complex stability.

*Types of Intermediates:*

1. Carbocation 

2. Carbanion 

*-I Effect (EDG):* 

- Stronger +I Effect (EDG) → Intermediate stability. 

2. Dipole Moment & Polarization: 

↑ Dipole Moment (μ) → ΔEN ↑  → polarization ↑

- More stable due to polarization ( complete transfer of electrons made them anion and cation).

*Order of I Effect Stability:*

- C-C-C-C-F > C-C-C-C-Cl > C-C-C-C-Br > C-C-C-C-I

*Dipole Moment:* 

·         When electronegativity difference (ΔEN) is less → there will be a displacement of electrons (sigma bonds). 

·         When ΔEN is high, the shifting of dipole moments increases. 

 

3. Acidic Character and +I Effect

*Acidic Character:*

-I Effect α Acidic character 

+I Effect → Reduces acidic character in electron donating groups (EDG).

*HA* → H⁺ + A⁻ 

- If A⁻ is stable → stronger acidic character.

*COOH* → COO⁻ + H⁺ 

The conjugate base (COO⁻) becomes more stable with the -I effect, increasing the acidic character.

*Example:*

a)

i) - F-CH₂-COOH 

ii) - Cl-CH₂-COOH 

iii) - Br-CH₂-COOH 

iv)  - I-CH₂-COOH 

The order of acidic character (based on –I Effect): 

Example (for acidic character):

F-CH₂-COOH > Cl-CH₂-COOH > Br-CH₂-COOH > I-CH₂-COOH

b)

i) CH₃-COOH 

ii) Cl-CH₂-COOH 

iii) Cl-CH₂- CH₂-COOH 

Cl-CH₂-COOH  > Cl-CH₂- CH₂-COOH  > CH₃-COOH  (Distance rule applied)