2. Definition
Process of electron shift along the chain of atoms due to the presence of
polar covalent bond in a molecule is known as inductive effect.
The inductive effect (I Effect) refers to the polarity produced in a molecule as
a result of higher electronegativity of one atom compared to another.
It involves sigma electrons. “SIGMA ELECTRONS MOVE IN THIS PROCESS”
3. The sigma electrons which form a covalent bond are seldom shared
between the two atoms. This is because different atoms have different
electronegativity values, i.e. Different powers of attracting the electrons in
the bond. Consequently, electrons are displaced towards the more
electronegative atom.
4. Consider the carbon-chlorine bond.
As chlorine is more electronegative, it will become negatively charged with
respect to carbon atom.
I. Indicates the relative charges on the two atoms.
II. The arrow head placed in the middle of the bond indicates the direction
in which the electron are drawn
III. The more heavily shaded part shows the region in which the electron
density is greatest.
5. This introduces a certain degree of polarity in the bond. the
electronegative atom acquires a small negative charge (δ–). The less
electronegative atom acquires a small positive charge (δ+).
An inductive effect is not confined to the polarization of one bond, it is
transmitted along a chain of carbon atoms, although it is insignificant
beyond the 3rd carbon.
6. Consider a carbon chain in which one terminal carbon atom is joined to a
chlorine atom. Chlorine has greater electronegativity than carbon.
Therefore the electron pair forming the covalent bond between the
chlorine atom and C1 will be displaced towards the chlorine atom. This
causes the chlorine atom to acquire a small negative charge and C1 a
small positive charge.
Since C1 is positively charged, it will attract towards itself the electron pair
forming the covalent bond between C1 and C2.this will cause C2 to
acquire aa small positive charge, but the charge will be smaller than that
on C1 because the effect of the chlorine atom has been transmitted
through C1 to C2. similarly, C3 acquires a positive charge which will be
smaller than that on C2.
This type of electron displacement along a chain is known as the Inductive
Effect.
7. Types :
1. -I effect
Atoms or groups which draw electrons away from a carbon atom are said to
have a -I effect . Such groups are referred as electron-attracting.
2. +I Effect
Atoms or groups which lose electrons towards a carbon atom are said to have
a +I effect . Such groups are referred as electron-releasing.
8. Relative Inductive Effects:
Relative inductive effects have been experimentally measured with
reference to hydrogen, The carbon-hydrogen bond is used as a standard.
Zero effect is assumed in this case.
in decreasing order of -I effect or increasing order of +I effect, as follows:
–NH3+ > –NO2 > –SO2R > –CN > –SO3H > –CHO > –CO > –COOH > –
COCl> –CONH2 >–F > –Cl > –Br > –I > –OR > -OH > –NH2 > –C6H5 > –
CH=CH2 > –H
The strength of inductive effect is also dependent on the distance between
the substituent group and the main group that react; the greater the
distance, the weaker the effect.
