Why is one of the three structures for C2H2Cl2 nonpolar
The Correct Answer and Explanation is:
C2H2Cl2 (dichloroethene) has three isomeric structures, and one of them is nonpolar. These isomers are cis-1,2-dichloroethene, trans-1,2-dichloroethene, and 1,1-dichloroethene. Let’s explore why one of them is nonpolar.
The trans-1,2-dichloroethene is nonpolar due to its symmetrical geometry. In this isomer, the two chlorine atoms are positioned opposite each other across the double bond of the ethene group. This arrangement results in the dipole moments of the two C-Cl bonds being equal in magnitude but opposite in direction. The opposite nature of these dipoles cancels each other out, leading to no net dipole moment for the entire molecule. As a result, the molecule does not exhibit polarity and is considered nonpolar.
In contrast, the cis-1,2-dichloroethene is polar because the two chlorine atoms are positioned on the same side of the double bond. This creates an asymmetrical distribution of electron density, and the dipole moments of the C-Cl bonds do not cancel out. Consequently, this isomer has a net dipole moment, making it polar.
The 1,1-dichloroethene molecule also has a polar nature, as the chlorine atoms are on the same carbon and there is no symmetry to allow for the cancellation of dipoles.
In summary, the trans-1,2-dichloroethene is the nonpolar isomer of C2H2Cl2 because of its symmetry, where the dipoles cancel each other out. This symmetry is a key factor in determining molecular polarity, and without it, as seen in the cis and 1,1 isomers, polarity persists.
