Inductive Effect

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Inductive Effect Chemistry

Inductive effect is a concept of general organic chemistry or GOC.

Now, you might wonder what GOC is.

Well, GOC stands for general organic chemistry. It is the ABC of organic chemistry which determines general things such as:

  1.  Acidic/basic order of any reaction

  2.  Probability of intermediates undergoing reaction

  3.  Inductive effect

In this article, we will study the inductive effect.

So, what is the Inductive Effect?

The inductive effect is one category of the electronic displacement effect. 

An electron displacement effect is an effect that electrons displace from their position.


Inductive Effect

Inductive effect is a partial shifting/displacement of σ electrons towards a more electronegative atom of σ bond.

This means σ  (or single bond electrons) shifts towards a more electronegative atom. Because of this, partial charges develop.

Let’s take inductive effect examples:

1. C-C-C-X

We can see a σ-bond between C and X, both sharing one electron.

Assume electronegativity of X > electronegativity of C. Then,

Both the electrons in this bond wish to shift towards X as it can pull more electrons towards itself. This process occurs in the following manner:

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Here, a partial negative charge develops on X, i.e., δ-, and a partial δ+ on one C-atom, and then proceeding to the left, on the second C-atom, the partial charge is δδ+, then on the third C-atom, it is δδδ+ and so on. 

As we can see, the magnitude of the partial charge decreases as we go to the left, i.e., away from X.

Since there was an electronegativity difference, that’s why the shifting occurred.

Here, X is an electron-withdrawing group or - I group because it withdraws electrons from Carbon.

This effect is also known as a negative inductive effect (- I effect) or electron-withdrawing inductive effect.

Let’s take an example of CH3Cl.

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Here, Cl is more electronegative than C, so partial δ- is formed on Cl and a partial δ+ on C.

2. C-C-C-Y

Here, Y is less electronegative than C-atom.

Here, C pulls σ-electrons towards itself, and on carbon, a partial negative charge appears as  δ-, while δ+ on Y-atom.

Here, Y is an electron-donating group or + I group because it donates electrons to Carbon.

This effect is also known as a positive inductive effect (+ I effect) or electron-donating inductive effect.

Note: Inductive effect considers the partial shifting of σ-electrons or a single bond only.


Order of Inductive Effect

Two types of order of inductive effect are:

1. - I order

We know that neutral species is more stable than the charged species.

We also need to know one thing, the more the charge distribution occurs, the more stable is the species. 

This means, if the charge remains static, the species remains unstable. Therefore, species must have a charge flow for it to remain stable.

Let’s talk about - I order for the other species:

NF3+  > NR+ > NH3+  > NO2 > - C ≡ N (cyanide group) > - CHO (aldehyde) > -RC (= O) R’ > - R - COOH > F > Cl > Br > I > - O - R > - O  H > - C ≡ CH > - NH2  ⋍ ⏣ > CH = CH2 > H

Points to Ponder:

Here, R stands for an alkyl group.

NF3+, NR+,  and  NH3are highly electronegative or high - I effect showing groups.

- C ≡ N → Cyanide group

- CHO →  Aldehyde group

- RC(= O)R’ → Ketone group

- R - COOH → Carboxylic acid group

- O - R → Epoxy group

- O - H → Alcohol group

- The order of - NH2  is approximately equal to Benzene (⏣).

- I effect of H  ⋍ zero.

Let’s determine the order of stability of the following species given below:

  1. F - CH2 - COO

  2. Cl - CH2 - COO-

  3. Br - CH2 - COO-

  4. I - CH2 - COO-

We know that F, Cl, Br, I are electronegative elements, and they all show - I effect.

Like in F - CH2 - COO

An electron from the electron cloud of COO- distributes to C in CH2, i.e., 

F ← CH2 ← COO-

Since the order of electronegativity is F > Cl > Br > I, this means Fluorine is the most electronegative element.

So, the maximum distribution of electrons will occur in F - CH2 - COO-.

Therefore, the stability order is:

(F - CH2 - COO- ) > (Cl - CH2 - COO-) > (Br - CH2 - COO-)  > (I - CH2 - COO-)

However, if the species has a positive charge like F - CH2 - COO+. Here, F tries to pull the electron from COO+ as it doesn’t have electrons for distribution. Therefore, 

F - CH2 - COO+ becomes unstable.

Let’s take another example of stability order:

NO2  - CH2  - COO- > F - CH2  - COO- >  CH = CH - COO-.

Note:

More the - I effect in the species is, more is its acidic order.

F - CH2 - COOH on releasing  H- becomes F - CH2 - COO-.

Similarly, the other species on releasing H- becomes Cl - CH2 - COO-, Br - CH2 - COO-, I - CH2 - COO-

We already know that F - CH2 - COOH is the most stable species. So, the acidic order will be F - CH2 - COOH > Cl - CH2 - COOH > Br - CH2 - COOH > I - CH2 - COOH.

2. + I order

CHΘ > NHΘ> OΘ> O > -COO > - C(CH3)3 > - H - C - (CH3)2 > -CH2 - CH3 > - CH3

Where,

- C(CH3)3 is 3° alkyl group

- H - C - (CH3)2 is 2° alkyl group

 -CH2 - CH3 is 1° alkyl group

- CH3 is a methyl group

∴ More the alkyl groups, more are the + I effect.

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FAQ (Frequently Asked Questions)

Q1: Why is the Inductive Effect Permanent?

Ans: Let’s take an example of C-C-C-Cl.

Here, Cl is an electronegative element. So, it withdraws electrons from the C-atom. A partial positive charge forms on the C-atom and this distribution or shifting is permanent. Therefore, the inductive effect is permanent.

Q2: What is the Resonance Effect?

Ans: The resonance effect is an effect on the stability of molecules with both single and double bonds, where a double bond means that there is a π-bond along with the σ-bond. The π-bond electron delocalization is the basis of the resonance effect. 

Here, not only π-electrons but also lone electron pairs may contribute.

The below diagram shows the resonance stabilization of the Carbonate ion.

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Q3: Is the resonance Effect Permanent?

Ans: Yes. In this process, the delocalization of electrons occurs because of which the chemical and physical properties change. Therefore, the resonance effect is permanent.

Q4: Write the differences between the Inductive and Resonance Effects.

Ans: The key differences between the inductive and the resonance effect are:

S.No.

Inductive effect

Resonance effect

1.

Partial displacement of charges takes place.

Complete displacement of charges takes place.

2.

The charges travel a short distance because of stronger bonds.

Therefore, it vanishes after four C-atoms.

It is distance independent.

Therefore, it operates up to the end of the conjugation system.