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 that determines general things such as:
Acidic/basic order of any reaction
Probability of intermediates undergoing reaction
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 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:
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 the 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.
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:
- I order
We know that neutral species are more stable than 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 NH3+ are highly electronegative or high - I effect showing groups.
Let’s determine the order of stability of the following species given below:
F - CH2 - COO-
Cl - CH2 - COO-
Br - CH2 - COO-
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-.
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.
+ I order
CHΘ > NHΘ> OΘ> O > -COO > - C(CH3)3 > - H - C - (CH3)2 > -CH2 - CH3 > - CH3
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.