Question

Correct order of dipole moment is:

A. $i = ii = iii$
B. $i < ii < iii$
C. $i > ii > iii$
D. $ii < iii < i$

Answer 1

Dipole moment is defined as the separation of the charges in the system. Both of the ionic and the covalently bonded compound tends to have the dipole moment. The reason for the cause of the dipole moment is the difference between the electronegativity of the chemically bonded atoms present in the molecule.

Complete step by step answer:
So the name of the compound (I)is the o- nitrophenol. The name of the (II)is 1,2 dichlorobenzene and the (III)is the 1,2 dimethylbenzene. The dipole moment as I said depends upon the electronegativity of the atom. So the electronegativity of the oxygen and nitrogen is greater than that of the chlorine and the methyl group. The dipole moment is pointed from the less electronegative atom towards the more electronegative atom. Due to the presence of the –R effect in the nitro group and the presence of the +R effect of the phenol the compound $(i)$ will have more dipole moment and then the 1,2 dichlorobenzene will have lees dipole than the $(i)$ but more than $(iii)$ as it is more electronegative whereas $(iii)$ will have the least dipole moment as it has the methyl group which is the least electronegative and is the electron donating group.

So the order is $i > ii > iii$ So the correct option is option c.

Note: The bond dipole moment tends to differ from that of the total dipole moment in the polyatomic molecule. The bond dipole moment is defined as the dipole moment which is present between the single bonded diatomic molecules. Whereas the total dipole moment in the polyatomic molecule is defined as the vector sum of all the bond dipoles present in the molecule.