There are three known compounds with the molecular formula of C2H2Cl2 but only one with the formula of C2H3Cl. Explain this in terms of molecular structure by drawing the four structures, identify which molecules are polar.
The Correct Answer and Explanation is:
The molecular formula C2H2Cl2 corresponds to three different compounds due to different structural arrangements of atoms. These compounds are 1,1-dichloroethene, cis-1,2-dichloroethene, and trans-1,2-dichloroethene. Similarly, there is only one compound with the formula C2H3Cl, which is chloroethene (vinyl chloride).
Let’s break down the structures and their polarity:
1. 1,1-Dichloroethene:
- Structure: Cl-CH=CH-Cl.
- In this structure, both chlorine atoms are attached to the same carbon atom.
- The molecule is polar because of the presence of two chlorine atoms on the same carbon, creating a dipole moment in the direction of the chlorine atoms.
2. Cis-1,2-Dichloroethene:
- Structure: Cl-CH=CH-Cl (with both chlorines on the same side).
- This molecule has a polar structure due to the difference in electronegativity between the carbon-hydrogen bonds and the chlorine atoms, creating a dipole along the axis of the molecule.
3. Trans-1,2-Dichloroethene:
- Structure: Cl-CH=CH-Cl (with chlorines on opposite sides).
- Despite having the same atoms, this molecule is non-polar. The dipoles cancel each other out because of the symmetry of the trans arrangement.
4. Chloroethene (C2H3Cl):
- Structure: CH2=CH-Cl.
- This molecule is polar because the chlorine atom is more electronegative than carbon, creating a dipole moment.
Polarity Summary:
- 1,1-Dichloroethene: Polar.
- Cis-1,2-Dichloroethene: Polar.
- Trans-1,2-Dichloroethene: Non-polar.
- Chloroethene: Polar.
The reason there is only one compound with the formula C2H3Cl is that the structure can only be chloroethene (vinyl chloride), where the hydrogen atoms are arranged in a specific way with chlorine.
This explanation highlights the importance of molecular symmetry and electronegativity in determining polarity.
