Question

Dipole Moment is shown by
A. 1,4-dichlorobenzene
B. Cis-1,2-dichloroethene
C. Trans-1,2-dichloroethene
D. Trans-1,2-dichloro-2-pentene

Answer 1

Hint: Difference in the electronegativity of two atoms results in the separation of charges the more electronegative atom attracts electrons toward it and becomes partially negative resulting a partial positive charge on the less electronegative atom. It does not break the bond between the two atoms.

Formula: $\mu=qr$ unit of dipole moment is Debye. It is direction dependent so it’s a vector quantity.
                Where; μ is the dipole moment,
                             𝑞 is the magnitude of charge,
                        𝑟 distance between charge

Complete step by step solution:
In the given organic compounds to determine if they show dipole moments or not first, we will draw the structures of these compounds.
A. 1,4-Dichlorobenzene
 1,4-dichlorobenzene is a symmetric molecule so the polarity generated by one chlorine atom will be neutralised by the other one so the overall polarity of the molecule will be zero because the chlorines are in the opposite directions so it will not have any dipole moment.

B. Cis-1,2-Dichloroethene
In cis-1,2-dichloroethene the direction of charges induced by both the chlorine is in the same direction so it will generate polarity in the molecule. So this organic compound will have a dipole moment


C. Trans-1,2-Dichloroethene
trans-1,2-dichloroethene is also a symmetric molecule so in trans-1,2-dichloroethene also the polarity generated by one chlorine atom will be neutralised by the other one so the overall polarity of the molecule will be zero because the chlorines are in the opposite direction so it will not have any the dipole moment.

D. Trans-1,2-Dichloro-2-Pentene
Trans-1,2-Dichloro-2-Pentene is not a symmetric molecule and polarity generated by chlorines will not be cancelled out by each other and so there will be a charge on the molecule and the molecule will become polar so the molecule will have a dipole moment.
  Thus, Option (B) & (D) is correct

Note: The polarity and dipole moment also helps in determining the reactivity of a compound.Because more polar compounds are more reactive than the less polar compound. Polarity of a compound also helps in determining the nature of the bond if it is ionic, covalent or polar covalent.