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How does adding several chlorine atoms affect the boiling point of a chlorinated methane compound?
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organohalogen compound
Vinyl chloride is an organohalogen compound that has important industrial applications. When treated with certain catalysts, vinyl chloride monomers undergo polymerization and form the larger compound known as polyvinyl chloride, or PVC. PVC is used in the manufacture of numerous products, including packaging films and water pipes.
For chlorinated methane compounds, adding several chlorine atoms consistently increases the boiling point. This trend occurs because the substitution of hydrogen atoms with chlorine increases the molecular weight and enhances the London dispersion forces between molecules, which are stronger in these larger, more polarizable structures.1
The progression of boiling points for these compounds demonstrates this clear increase:
- Methyl chloride (CH₃Cl): −24 °C (−11 °F)12
- Dichloromethane (CH₂Cl₂): 40 °C (104 °F)13
- Chloroform (CHCl₃): 61 °C (142 °F)1
- Carbon tetrachloride (CCl₄): 77 °C (171 °F)14
This behavior contrasts with multiple fluorine substitution, which can lower boiling points by reducing overall molecular polarizability.1