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Complete Chemistry of Inductive Effect Observed in Organic Molecule.

Updated on November 18, 2015

List of Topics Included

(1) What is called inductive effect?

(2) Symbolic representation of inductive effect

(3) Some characteristics of inductive effect

(4) Importance of study of inductive effect

(5) Types of inductive effect
(5/A) Positive (+I) inductive effect
(5/B) Negative (-I) inductive effect

(6) Application of inductive effect

(6/A) Reactivity of various alkyl halides

(6/B) Relative strength of carboxylic acids
(6/B/1) Effect of electron withdrawing group on acidic strength of carboxylic acids
(6/B/2) Effect of electron donating group on acidic strength of carboxylic acids

(6/C) Relative basic strength of various amines
(6/C/1) Effect of electron donating group on basic strength of amines
(6/C/2) Effect of electron withdrawing group on basic strength of amines

(6/D) Stability of carbocations
(6/D/1) Classification of carbocations
(6/D/2) How +I or -I effect stabilizes or destabilizes carbocation?

(6/E) Stability of carbanions

(6/E/1) Classification of carbanions

(6/E/2) How +I or -I effect stabilizes or destabilizes carbanions?

(7) References

(1) What is called, “Inductive Effect?”

It is partial displacement of shared electrons in a single hetero covalent bond.

It takes place due to reason that, in a hetero bond of organic molecule, two dissimilar atoms (or groups) have different characteristic attraction towards electrons. Hence, the shared electron pair remains closer to more electronegative atom or group. In other words, the more electronegative atom will have higher electron density.

This gives rise to permanent partial negative charge on more electronegative atom, and equal amount of positive charge on another atom of the bond.

Such permanent displacement of shared electron in a covalent bond of organic compound is known as, “inductive effect”.

(2) Symbolic Representation of Inductive Effect

The symbolic representation of inductive effect is based on following points.

(1) The partial positive or negative charges resulted as explained above, are denoted with a Greek symbol-δ (small delta). Partial positive charge is denoted with symbol: δ+ while partial negative charge is denoted with: δ-.

(2) The direction of displacement of electron is denoted with an arrow pointed towards more electronegative atom.

(3) The effect of displacement of electron density extends to adjacent atoms also, but its strength (means intensity of charge) decreases with increase in distance. The decreasing electronic charge is denoted with increase in number of signs of delta.

This will be clear from the following picture.

Inductive Effect Decreases With Distance

More is number of delta, lesser is intensity of charge.
More is number of delta, lesser is intensity of charge.

(3) Some Characteristics of Inductive Effect

(1) It is permanent effect.

(2) It is of two types:

(a) Positive inductive effect, shown by +I symbol and

(b) Negative inductive effect, shown by -I symbol.

(3) It extends through sigma bonds.

(4) Its influence is observed up to fourth carbon of chain, but its effect is significant only up to second carbon.

(5) It affects physical properties (like: dipole moment, melting point etc.) as well as chemical properties (like: stability, reactivity, acidic/basic strength etc.) of the compound.

(4) Importance of Study of Inductive Effect

Due to inductive effect, some special characteristic properties are produced in the compound as discussed below.

(a) The reactivity of compound, towards certain reagent, either increases or decreases due to presence of a particular functional group. This can be easily understood by inductive effect of that functional group.

(b) In case the compound is acid, its acidic strength can be predicted, compared and modified based on inductive effect.

(c) In case the compound is base, its basic strength can be predicted, compared and modified based on inductive effect.

(d) Stability of some intermediates like carbocations and carbanions can be understood.

(e) Feasibility of certain reactions can be predicted.

(5) Types of Inductive Effects

Depending upon electron donating or electron withdrawing characteristic of functional group, inductive effect is divided into two categories:

(1) +I effect and

(2) -I effect.

It must be noted that electron donating or electron withdrawing capacity of a group is determined taking hydrogen as a reference.

If capacity of a group to withdraw electron is more than that of hydrogen, it is called electron withdrawing group.

Likewise if capacity of a group to withdraw electron is less than that of hydrogen, it is called electron donating group.

The detailed information about both of these effects is given in the following paragraph.

(5/A) Positive Inductive Effect (+I Effect)

If an electron donating substituent is attached to the end of carbon chain, it pushes electrons towards carbon atom and thereby increases electron density on adjacent carbon atom. As its effect on adjacent carbon is positive with reference to electron density, it is defined as, “positive inductive effect”. Such effect is denoted by symbol “+I”.

Which groups give positive inductive effect?

Only alkyl groups (or substituents) can produce such effect.

However, intensity of +I effect produced by all alkyl groups, is not same.

It is observed that, +I effect of an alkyl group depends upon number of carbon atoms it contains. More is number of carbon atoms in a given alkyl group, higher is its electron donating capacity, stronger is +I effect it produces.

The order of increasing +I effect of some common alkyl groups is shown below:

H < methyl (-CH3) < ethyl (-C2H5) < propyl (-C3H7) < iso propyl {-CH(CH3)2} < tert-butyl {C(CH3)3}.

(5/B) Negative Inductive Effect (-I Effect )

If an electron withdrawing substituent is attached to the end of carbon chain, it attracts electrons from carbon atom and thereby decreases electron density on adjacent carbon atom. As its effect is negative with reference to electron density, it is defined as, “negative inductive effect”. Such effect is denoted by symbol “-I”.

Which groups give negative inductive effect?

The groups containing atoms of electronegative elements produce negative inductive effect.

The order of increasing -I effect of some common groups is shown below:

H < phenyl (-C6H5) < iodo (-I) < bromo (-Br) <chloro (-Cl) < fluoro (-F) < carboxyl (-COOH) < cyanide (-CN) < nitro (-NO2).

(6) Application of Inductive Effect

Inductive effect either produces or increases charge separation in the organic molecule.

Due to partial positive and negative charges produced thus, an organic molecule exhibits some special characteristic properties like: reactivity, stability, acidity, basicity etc.

(6/A) Understanding relative reactivity of various alkyl halides

Why reactivity of alkyl halides, compared to corresponding alkanes is always more?

The high reactivity of alkyl halide is result of:

(a) Positive inductive effect of alkyl group and

(b) Negative inductive effect of halo group.

Due to this, halogen atom of an alkyl halide can readily depart as halide anion. In other words, it is due to inductive effect halogen can act as a better leaving group during substitution reaction.

This facilitates nucleophilic substitution reaction in alkyl halide.

However, due to absence of such inductive effect in alkanes they can not easily react.

It is due to above reason, that alkyl halides are more reactive than corresponding alkanes.

This will be clear from following examples:

(a) Methyl chloride is more reactive than methane due to +I effect of methyl group and -I effect of chloro group.

(b) Tertiary butyl chloride is more reactive than isomeric normal butyl chloride, because former has triple +I effect of three alkyl groups, while later has +I effect of only one alkyl group.

(6/B) Understanding relative strength of Carboxylic Acids

The relative strengths of various carboxylic acids are expressed in terms of their ionization constant values-Ka. Higher is the value of Ka, stronger is the acid (or lower is the value of pKa stronger is the acid).

However, the acidic strength of carboxyl (-COOH) group is due to the fact that, strong -I effect of two oxygen atoms withdraw electron density from hydrogen and compel it to pass in the solution as H+ ion, leaving behind two bonded electrons.

RCOOH → RCOO- + H+

The presence of substituent group modifies the strength of acid as explained in following two cases.

(6/B/1) Effect of Electron Withdrawing Group on Strength of carboxylic Acid

Carboxylic acid contains two oxygen atoms. Due to electron withdrawing effect of these oxygen atoms, hydrogen passes in the solution.

However, presence of any other electron withdrawing group in the carbon chain enhances the capacity of two oxygen atoms to withdraw electrons from hydrogen. This facilitates removal of H+ ion, to make acid more powerful.

[Alternately, this can also be explained in the light of stability of carboxylate anion (RCOO-) produced after removal of H+ ion from acid. This is discussed below.

Due to electron withdrawing (-I) effect of such group, the intensity of negative charge of carboxylate anion decreases (negative charge gets dispersed), which makes it more stable.

Due to this, more and more acid dissociates to produce stable carboxylate anion with simultaneous yield of H+ ions. This makes acid stronger.]

For example: Monochloroacetic acid is stronger than acetic acid.

The table below shows effect of electron withdrawing groups on pKa values of some acids. Less is pKa value stronger is acid.

Table showing increase in acidic strength due to increasing -I effect of group present in acid

Name of acid (itsformula)
Value of its ionization constant-Ka
Its pKa value
Acetic acid(CH3-COOH)
1.76x10(-5)
4.74
Monochloro acetic acid(Cl-CH2-COOH)
135x10(-5)
2.88
Dichloro acetic acid(Cl2-CH-COOH)
5532x10(-5)
1.27
Trichloro acetic acid(Cl3-C-COOH)
23200x10(-5)
0.64
Benzoic acid(C6H5-COOH)
6.44x10(-5)
4.21
p-Chloro benzoic acid(p-Cl-C6H4-COOH)
1.072x10(-4)
3.97
p-Nitro benzoic acid(p-NO2-C6H4-COOH)
36x10(-5)
3.44
Progressive introduction of "chloro" groups, results in progressive increases of acidic strengths of various chloro acids. Similarly, introduction of "chloro" and "nitro" groups, increases acidic strength of benzoic acid.

Acidic Strengths of Various Chloro acids (-I effect)

Increase in number of chloro groups results in increased acidic strength.
Increase in number of chloro groups results in increased acidic strength. | Source

(6/B/2) Effect of Electron Donating Group on Strength of Acid

How presence of electron donating group in the carbon chain decreases acidic strength?

Such group, by supplying electrons towards -COOH group, retards the capacity of two oxygen atoms to withdraw electrons from hydrogen. This hinders the departure of H+ ion, and renders acid less powerful.

[Alternately, this can also be explained in the light of stability of carboxylate anion (RCOO-) produced.

Due to electron releasing (+I) effect of such group, the intensity of negative charge of carboxylate anion increases, which makes it less stable. Due to this, acid will not dissociate further to yield more H+ ions. This makes acid weaker.]

For example, acetic acid is weaker than formic acid.

The table below shows effect of electron donating groups on pKa values of some acids.

Table Showing Decrease in Acidic Strength due to Increasing +I Effect of Group present in Acid

Name of acid (its formula)
Value of ionization constant-Ka
Its pKa value
Methanoic acid(H-COOH)
17.73x10(-5)
3.74
Ethanoic acid(CH3-COOH)
1.73x10(-5)
4.74
Propanoic acid(CH3-CH2-COOH)
1.3x10(-5)
4.86
Benzoic acid(C6H5-COOH)
6.46x10(-5)
4.21
p-Methyl benzoic acid(p-CH3-C6H4-COOH)
4.21x10(-5)
4.41
Due to increasing +I effect of methyl to ethyl to propyl group, acidic strength decreases from methanoic to ethanoic to propanoic acid. Similarly +I effect of methyl group decreases acidic strength of benzoic acid.

Due to Increasing +I Effect of Alkyl Group Acidic Strength Decreases

+I effect increases from hydrogen to methyl to ethyl group. This causes decrease in acidic strength of methanoic acid to ethanoic acid to propanoic acid.
+I effect increases from hydrogen to methyl to ethyl group. This causes decrease in acidic strength of methanoic acid to ethanoic acid to propanoic acid. | Source

(6/C) Understanding relative basic strengths of various Amine Compounds

In aqueous solution, amine compound react with water to yield free hydroxyl anion, which is responsible for its basic character.

R-NH2 + H2O → R-NH3+ + OH-.

The basic strength of various amine compounds is due to availability of two unshared electrons resting on nitrogen atom, which undergoes protonation with water.

If electrons of amine compound are readily available, quantity of free hydroxyl anion produced is more, relative basic strength of amine is more; and vice versa.

The strength of base is given in terms of ionization constant constant (Kb), higher the value of Kb stronger is the base.

However, the strength of base is also given in terms of pKb value, lesser is pKb value, stronger is the base.

(6/C/1) Effect of Electron Donating Group

Such group, by pushing electrons towards nitrogen atom, increases electron density around nitrogen. This enhances the capacity of amine to release electrons, which in turn favours protonation. This makes amine stronger base.

[Alternately, this can also be explained in the light of stability of ammonium cation (RNH3+) produced.
Due to electron donating (+I) effect of such group, the intensity of positive charge on ammonium cation decreases (positive charge gets dispersed), which makes it more stable. Due to this, more and more amine molecules react with water to produce hydroxyl anions. This makes amine a stronger base].

For example, methyl amine is stronger base than ammonia.

Table showing increase in basic strength(decrease in pKb value) due to increasing +I effect of group present in amine.

Name of base or amine (its formula)
Value of its ionization constant-Kb
Its pKb value
Ammonia(NH3)
1.78x10(-5)
4.77
Methyl amine(CH3-NH2)
4.52x10(-4)
3.38
Ethyl amine(CH3-CH2-NH2)
5.12x10(-4)
3.29
Aniline(C6H5-NH2)
4.22x10(-10)
9.38
p-Methyl aniline(p-CH3-C6H4-NH2)
1.22x10(-9)
8.91
It is clear from above data that a group having stronger +I effect increases relative strength of amine.

(6/C/2) Effect of Electron Withdrawing Group on Basic Strength of Amine

Such group, by attracting electrons from amine, decreases electron density on nitrogen, which in turn hinders protonation. This makes amine a weaker base.

[Alternately, this can also be explained in the light of stability of ammonium cation (RNH3+) produced. Less is its stability weaker is the amine as a base.

Due to electron attracting (-I) effect of such group, the intensity of positive charge on ammonium cation increases, which makes it unstable. This hinders protonation to yield hydroxyl anions. Due to this, lesser amine reacts with water to produce hydroxyl anion. This makes amine a weaker base].

For example, aniline is weaker base than ammonia.

Table Showing Decrease in Basic Strength (Increase in pKb value) Due to Increasing -I Effect of Group Present in Amine

Name of amine (its formula)
Value of its ionization constant-Kb
Its pKb value
Aniline(C6H5-NH2)
4.22x10(-10)
9.38
p-Chloroaniline(p-Cl-C6H4-NH2)
9.55x10(-11)
10.02
p-Nitroaniline(p-NO2-C6H4-NH2)
1.02x10(-13)
12.98
Please note that both "chloro" and 'nitro" are electron withdrawing groups, hence both of them decreases basic strength of amine. However, due to higher electronegativity of nitro group than that of chloro group, para-nitroaniline is weaker base than

(6/D) Understanding Stability of Carbocation

What is meant by carbocation?

Carbocations are the reactive intermediates, produced during some complex organic reactions.

They contain such carbon atom, which has only six electrons around it, instead of eight, as required by “octet rule”.

Due to electron deficiency, carbocations always bear positive charge.

In a reaction mixture, they always remain in search of electrons to which they can combine to nullify their charge, to complete their octet.

In this way, carbocations are very reactive species.

(6/D/1) Classification of Carbocations

Depending upon number of other carbon atoms to which positively charged carbon atom is joined carbocations are classified into three different categories as given below.

(1) Primary (10) carbocations:

These are such carbocations, in which positively charged carbon is joined with only one more carbon atom. For example: ethyl carbocation.

(2) Secondary (20) carbocations:

These are such carbocations, in which positively charged carbon is joined with two more carbon atoms. For example: isopropyl carbocation and sec-butyl carbocation.

(3) Tertiary (30) carbocations:

These are such carbocations, in which positively charged carbon is joined with three more carbon atoms. For example: tert-butyl carbocation.

(6/D/2) How +I or -I Effect, Stabilizes or Destabilizes Carbocations?

(1) If a carbocation has very intense positive charge, it will immediately attract some electron rich species present in the reaction mixture and will soon combine with it to become stable.

This means such carbocations are transient (means short lived). Such carbocations are not stable, but are reactive.

(2) On the other hand, if a carbocation has very weak positive charge, it can not attract electron rich species immediately, hence it can remain alive in reaction mixture for longer period. Such carbocations are stable.

Thus, stability of carbocation depends upon intensity of positive charge they bear.

(a) The tertiary carbocations are most stable, because they are joined with three different alkyl groups, which decrease intensity of positive charge by releasing electron through triple +I effect.(Remember alkyl groups have +I effect).

(b) On the contrary, primary carbocations are least stable, as they have only one alkyl group. (Methyl carbocation is least stable, as it has no alkyl group at all).

(c) Secondary carbocations are intermediate of above two.

Therefore, the stability of various carbocations increases in following order:
methyl carbocation < 10 carbocation < 20 carbocation < 30 carbocation.

See the following picture.

Increasing Stability of Carbocation With Increase in Alkyl Groups

As the number of alkyl groups increases, they push more and more electrons towards positively charged carbon atom of carbocation. This causes dispersion (means dilution) of positive charge, resulting in increased stability.
As the number of alkyl groups increases, they push more and more electrons towards positively charged carbon atom of carbocation. This causes dispersion (means dilution) of positive charge, resulting in increased stability. | Source

(6/E) Understanding Stability of Carbanions

What is called carbanion?

As like carbocations, they are also intermediate produced during complex organic reaction.

They contain such carbon atom, which has eight electrons around it, and negative charge. Due to negative charge, they always remain in search of positive charge to which they can combine to nullify their charge, to become stable.

Thus, carbanions are also reactive species.

However, stability of carbanions can be explained just by opposite consideration to that of carbocations, because they carry negative charge which is opposite to that carried by carbocations.

(6/E/1) Classification of Carbanions

Depending upon number of other carbon atoms to which negatively charged carbon atom is joined, carbanions are classified into three different categories as given below.

(a) Primary (10) carbanions:
These are such carbanions in which negatively charged carbon is joined with only one more carbon atom. For example: ethyl carbanion.

(b) Secondary (20) carbanion:
These are such carbanions in which negatively charged carbon is joined with two more carbon atoms. For example: isopropyl carbanion.

(c) Tertiary (30) carbanions:
These are such carbanions in which negatively charged carbon is joined with three more carbon atoms. For example: tert-butyl carbanion.

(6/E/2) How +I or -I Effect, Stabilizes or Destabilizes Carbanions?

(1) If a carbanion has very intense negative charge on it, it will immediately attract some positively charged species present in the reaction mixture to combine with it to become stable. Such carbanions are thus unstable and transient (means short lived).

(2) On the other hand, if a carbocation has very weak negative charge on it, it can’t easily attract oppositely charged species present in the reaction mixture, hence it can remain alive in reaction mixture for longer period. Such carbanions are stable carbanions.

Thus, stability of carbanions depends upon intensity of negative charge they bear.

(a) The tertiary carbanions are least stable, because they are joined with three different alkyl groups, which push electrons towards them and increase intensity of negative charge on them. Due to intense negative charge they become more reactive or unstable.

(b) On the contrary, primary carbanions are most stable, as they have only one alkyl group which pushes electrons towards them. Thus lesser intensity of negative charge makes them comparatively stable. (Methyl carbanion is most stable, as it has no alkyl group at all).

(c) Secondary carbanion is intermediate to above two.

Hence, stability of carbanions decreases in the following order:
methyl carbanion > 10 carbanion > 20 carbanion > 30 carbanion.

Decreasing stability of Carbanions with Increase in number of alkyl groups

More is number of alkyl groups more they push electrons to negatively charged carbon atom lesser is stability of carabanion.
More is number of alkyl groups more they push electrons to negatively charged carbon atom lesser is stability of carabanion.

(7) References

(1) Organic Chemistry by: Robert Thornton Morrison and Robert Neilson Boyd, Seventh Edition, Published by, "Dorling Kindersley(India) Pvt. Ltd., licensees of Pearson Education in South Asia

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(3) Oxford Dictionary Of Chemistry, published by Oxford University Press Inc., New York

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(7) Fundamentals Of Chemistry, Class 11, by J. D. Lee, Solomons & Fryhle, Published by: Wiley India Pvt. Ltd., 4435-35/7, Ansari Road, Daryaganj, New Delhi-110002

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(10) Organic Chemistry, by Bhupinder Mehta & Manju Mehta, Published by: Prentice-Hall Of India Private Limited, M-97, Connaught Circus, New Delhi, -110001, India

(11) Nootan ISC Chemistry, Class XI & XII, by Dr. H. C. Srivastava, Published by: Nageen Prakashan (Pvt.) Ltd., 310, Western Kutchery Road, Meerut-250001, U.P., India

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