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Inductive effect results in permanent polarisation in a carbon chain, which arises due to partial displacement of covalently bonded electrons toward more electronegative atoms. Electrons are not completely transferred from one atom to another atom. Inductive effect is transmitted from one end of the chain to the other. Inductive effect keeps on decreasing with distance along the chain.
Read Also: Charging by Induction
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Key Takeaways: Inductive effect, polarisation, covalent bond, sigma bond, Electron affinity, Electronegativity
Inductive effects
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Inductive effect is a displacement of an electron along the carbon chain due to the presence of an electron-withdrawing or electron releasing group.
- Its effect is permanent. Inductive effects are transmitted along the chain. Inductive effects result from differences in electronegativities.
- Inductive effect weakens steadily with increasing distance from the substitution (electron-withdrawing or electron-donating) group and is actually negligible after three carbon atoms.
Types of Inductive effects
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There are two types of inductive effect i.e. – I effect and +I effect.
Negative Inductive effect (I- Effect)
When the substituent attached to the end of the carbon chain is electron-withdrawing (X), the effect is called negative induction effects (– I effect).
I- effect decreases with distance, as one goes away from groups (electron attracting).
C1(δ+) > C2(δδ+) > C3 (δδδ+) and other third carbon charge is negligible.
Negative inductive effect (I- effect) of different functional groups in decreasing order:
NO2 > F > COOH > Cl > Br > I > OH > C6 H5
Positive inductive effect (I+ effect)
When the substituent attached to the end of the carbon chain is electron donating, the effect is called positive inductive effect (+I effect).
This is due to electron releasing of the group, it develops a negative charge on the chain.
Positive inductive effect (+I effect) also decreases as we go away from substitution group (electron releasing nature)
So +I effect is in order of:
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Acidic and Basic Nature due to Inductive effects
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Negative inductive effect (-I effect): Due to electron-withdrawing nature of the group, electron density decreases. Thus, basic nature is decreased and acidic nature is increased.
Positive inductive effects (+I effect): Due to electron releasing of the group electron density is increased. Thus, basic nature is also increased and naturally acidic nature is decreased.
| Particulars | -I effect | +I effect |
|---|---|---|
| Acidic Nature | Increase | Decrease |
| Basic Nature | Decrease | Increase |
Check Also: Charge Transfer
Difference between the Positive and Negative Inductive effects
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Following are the Differences:
| +I effect | -I effect |
|---|---|
| Is due to the electron releasing group. | Is due to electron-accepting groups. |
| Electronegativity is less than Hydrogen. | Electronegativity is greater than Hydrogen. |
| Groups showing +I effect, disperses partial negative charge on the C-chain. | Group showing –I effect disperses positive charge on the C-chain . |
Effects of inductive effects
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Following are some effects:
- Induction effect stabilised carbocation and carbanion.
- Induction effect stabilises free radicals.
- Effects of acidic and basic nature of acids and bases.
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Points to Remember
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Following are some important points:
- The phenomenon of inductive effect helps in clarifying the mechanism of many reactions and many other facts.
- Because of the Inductive effect polar compounds have high melting point, boiling point and dipole moment.
- Inductive effect operates via sigma(σ) bonded electrons.
- Inductive effect is the distance-dependent effect. As distance increases, its effect decreases. Inductive effects can be neglected after the third carbon.
- Inductive effect has a destabilizing effect.
Read More: Organic compounds
Sample Questions
Ques: Give example of negative inductive effect. (3 Marks)
Ans: Chloroacetic acid is stronger than acetic acid since Cl shows negative inductive effect decreasing electron density. O – H bond is weakened causing ionisation of the carboxyl group(-COOH) to a greater extent than CH3COOH.
NH3 is a base due to the presence of lone pairs on nitrogen. Phenyl is an electron-withdrawing group. Due to this electron density of nitrogen in aniline decreases. Thus, aniline is a weaker base than NH3.
Ques: Inductive Effect vs Electromeric Effect (3 Marks)
Ans: Key differences between the electromeric and the inductive effects:
| Particulars | Inductive Effect | Electromeric Effect |
|---|---|---|
| Works on: Bond | sigma bonds | pi bonds |
| Nature | The inductive effect is permanent. | The electromeric effect is a temporary effect. |
| Dependency | Doesn’t require any attacking reagent | Electrophilic attacking reagent is required |
Ques: What is the functionality of the inductive effect? (2 marks)
Ans: Inductive effect imposes polarity in a compound. Because of Inductive polar compounds have high melting point, boiling point and dipole moment. The phenomenon of inductive effect helps in clarifying the mechanism of many reactions and many other facts. Induction effect stabilised carbocation and carbanion. Induction effect stabilises free radicals.
Ques: Giving justification, categories the following molecules or ions as nucleophile or electrophile: HS−, BF3, C2 H5 O−, (CH3)3 N, Cl−, CH3 C+=O, H2 N−HS−, BF3 , C2H5O−, (CH3)3N, Cl−, CH3C+=O, H2N− (3 marks)
Ans: Nucleophiles: HS−, C2H5O−, (CH3)3N, H2N−HS−, C2H5O−, (CH3)3N, H2N− have unshared pair of electrons which can be donated and shared with an electrophile.
Electrophile: BF3, Cl+, CH3C+BF3, Cl+, CH3C+ have only six electrons which can accept electrons from a nucleophile.
Ques: What is electronegativity? (4 Marks)
Ans: Electronegativity of an element is the tendency of its atoms to attract the shared pair of electrons towards itself in a covalent bond. Electronegativity depends on:
- State of hybridization: An sp-hybridised carbon is more electronegative than sp2 hybridised carbon. And sp2 is more electronegative than a sp3 hybridised carbon.
- Oxidation state of element: When oxidation state of an element increases, its electronegativity also increases.
- Nature of the substituents attached to the atom: The electronegativity values for the elements increases along a period from left to right and decreases down a group in the periodic table.
Ques: What is a positive inductive effect? Why do alkyl groups show positive inductive effects? (3 Marks)
Ans: When the substituent attached to the end of the carbon chain is electron donating, the effect is called positive inductive effect (+I effect).
This is due to electron releasing of the group, it develops a negative charge on the chain.
Alkyl groups (CH3) show positive inductive effects because of partial positive charge on hydrogen atom and partial negative charge on carbon atom in C-H bonds. So, each hydrogen atom acts as an electron donating group. This collective effect of electron donation by hydrogen atoms turns the alkyl group into an electron donating group.
Ques: What is resonance? (3 Marks)
Ans: A number of organic compounds cannot be accurately represented by one structure. For example, the structure of benzene has three C-C bonds and three C=C bonds. Now, C-C and C=C bonds are of different length. But it is experimentally found that all carbon-carbon bonds in benzene are identical and have the same bond length. Thus, benzene cannot be represented by a single structure. It can be represented equally well by the structure which is energetically similar to structures I and II. The two structures (I and II) are called resonance structures.
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