Question

Negative inductive effect is shown by:
A. $C{H_3}$
B. $- C{H_2}C{H_3}$
C. $- N{H_3}$
D. ${(C{H_3})_2}CH$

Answer 1

Electron withdrawing group shows negative inductive effect and electron releasing group shows positive inductive effect.

Complete step by step answer: We know that inductive effect is the effect of displacement of $\sigma$ electrons along a saturated carbon chain whenever an electron withdrawing or electron donating group is present at the end of the chain.
There are 2 types of inductive effects that are +I effect and -I effect. If the substituent attached to the end of the carbon chain is Electron donating, the effect is called +I effect. Whenever an electron donating Atom(Let group be -X) Is attached To the end of the carbon chain , The $\sigma$ electrons of C-X bond are displaced away from C-X bond. As a result , the atom X acquires a small positive charge ( that is ${\partial ^ + }$ ) and $C_1$ acquires a small negative charge (that is. ${\partial ^ - }$ ) as shown below:-
${C_4} - {C_3}^{\partial \partial \partial - } \to {C_2}^{\partial \partial - } \to {C_1}^{\partial - } \to {X^{\partial + }}$
Similarly ${C_2}$ and ${C_3}$ atom acquires more small negative charge ( that is $\partial {\partial ^ - }$ and $\partial \partial {\partial ^ - }$ respectively) The +I effect of some of the atoms or groups in decreasing order with respect to hydrogen is :-
${(C{H_3})_3}C \to {(C{H_3})_2}CH \to C{H_3}C{H_2} \to C{H_3} \to H$
The other type of inductive effect is -I effect. If the substituent attached to the end of the carbon chain is electron withdrawing, the effect is called -I effect. For example:-
${C^{\partial \partial \partial + }} \to {C^{\partial \partial + }} \to {C^{\partial + }} \to {X^{\partial - }}$ (where X electron is withdrawing substituent)
The negative inductive effect (that is -I effect) of some of the atoms or groups in decreasing order with respect to hydrogen is:-
$- N{O_2} > - CN > - COOH > - F > - Cl$
From above we got to know that $- C{H_3}, - C{H_2}C{H_3}$ and $CH -$ groups are electron donating groups and thus show positive inductive (that is +I effect)
So we have only the -$N{O_2}$ group in the option which shows a negative inductive effect (that is -I effect).
So, the correct answer is “Option C”.

Note: Inductive effect is a permanent effect operating in the ground state of organic molecules and hands is responsible for high melting boiling point and dipole moment of polar compounds. Moreover this effect weakens steadily with increasing distance from substituent.