Question

Which of the following has a correct negative inductive effect(-I) order.
a) $- N{O_2} > - CN > - COOH$
b) $- F > - Cl > - Br > - I$
c) $- \mathop N\limits^ \oplus {H_3} > - \mathop N\limits^ \oplus {H_2} > - \mathop N\limits^ \oplus HM{e_2} > \mathop { - N}\limits^ \oplus M{e_3}$
d) $- C \equiv CH > - ph > - CH = C{H_2}$

Answer 1

Hint : Inductive effect can be defined as the polarization of a sigma bond caused by the polarization of the adjacent sigma bond.There are two types of inductive effect-Negative inductive effect(-I) and Positive inductive effect(+I).

Complete Step By Step Answer:
When covalent bond is forms between two atoms which differ in electronegativity the electron density gets shifted towards the more electronegative atom in that.This results in polarity in covalent bonds.Such a polarization in covalent bond is termed as Inductive effect.It’s important to note that inductive effect is present in ( $\sigma$ )sigma bonds.There are two types of inductive effect-Negative inductive effect(-I) and Positive inductive effect(+I).Atoms or group of atoms which are highly electronegative act as electron withdrawing group and are said to exhibit negative inductive effect.On the contrary atoms or group of atoms which are highly electropositive act as electron withdrawing group and are said to exhibit positive inductive effect.
According to the negative inductive series $- N{O_2} > - CN > - COOH$ and $- F > - Cl > - Br > - I$ Hence we can conclude that option (a) and option (b) are correct.
The negative inductive series has already determined that $- \mathop N\limits^ \oplus {H_3}$ wields the highest -I effect.Also it has been experimentally proved that substitution of $- H$ group in $- \mathop N\limits^ \oplus {H_3}$ with Methyl group lowers the -I effect of the latter.Hence we know that option (c) is also correct.
However, according to the negative inductive series $- ph$ wields a higher -I effect than $- C \equiv CH$ but in option (d) $- C \equiv CH$ is placed first hence option (d) is incorrect.
Correct options- (a),(b),(c).
Incorrect option-(d)

Note :
Unlike mesomeric effect which occurs in $\pi$ bonds inductive effect is seen in ( $\sigma$ )sigma bonds.Inductive effect helps in deciding various factors like reactivity,stability,acidity and basicity of compounds