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what is Inductive effect ?
The normal C–C bond has no polarity as two atoms of same electronegativity (EN) value are connected to each other. Hence the bond is nonpolar. Consider a carbon chain in 1-Chloro butane, here due to more EN of Cl atom C–Cl bond pair is slightly displaced towards Cl atom hence creating partial negative (d–) charge over Cl atom and partial positive (d+) charge over C1 atom.
Now since C1 is slightly positive, it will also cause shifting of C1–C2 bond pair electrons towards itself causing C2 to acquire small positive charge. Similarly C3 acquires slightly positive charge creating an induction of charge in carbon chain. Such an effect is called inductive effect.
Diagram showing I effect.
The arrow shows electron withdrawing nature of –Cl group.
D1: Thus inductive effect may be defined as a permanent displacement of s bond pair electrons due to a dipole. (Polar bond)
Some important points are:
(a) It can also be defined as polarisation of one bond caused by polarisation of adjacent bond.
(b) It is also called transmission effect.
(c) It causes permanent polarisation in molecule, hence it is a permanent effect.
(d) The displacement of electrons takes place due to difference in electronegativity of the two atoms involved in the covalent bond.
(e) The electrons never leave their original atomic orbital.
(f) Its magnitude decreases with distance and it is almost negligible after 3rd carbon atom.
(g) The inductive effect is always operative through s bond, does not involve p bond electron.
1.1 Types of inductive effects:
D2: (a) –I Effect: The group which withdraws electron cloud is known as –I group and its effect is called –I effect. Various groups are listed in their decreasing –I strength as follows.
> – > – > –NO2 > –SO2R > –CN > –SO2Ar > –COOH > –F > –Cl >
–Br > –I > –OAr > –OR > –SR > –OH > –CºCR > Ar > –CH=CR2
D3: (b) +I effect: The group which release electron cloud is known as +I group and effect is +I effect.
> > –C(CH3)3 > –CH(CH3)2 > –CH2–CH3 > –CH3 > –D > –H
The hydrogen atom is reference for +I and –I series. The inductive effect of hydrogen is assumed to be zero.
Ex. Since – NO2 is –I group it pulls or withdraws electron from cyclohexane ring making it electron deficient
Ex. Let us consider effect of COOH & – COO– in carbon chain
Due to e– donating nature of carbon chain has become partially negative but –COOH is –I group therefore carbon chain has become partially positive.
Ex. Direction of electron displacements
- 2. 3.
- 5. 6.