Naming Freons
As part of the marketing plan, Du Pont developed a numbering system to refer to the chlorofluorocarbons. Each species of CFC is given a number which can be used to determine its structural formula. For example, trichlorofluoromethane (CFCl3) is Freon-11. (See CFC-11) The formula for decoding this system is simple.
Add 90 to the Freon number and interpret the three digit result according to the following system: the left digit is the number of carbon atoms, the middle digit is the number of hydrogen atoms, and the right digit is the number of fluorine atoms. Conspicuous by its absence is chlorine. All the bonding sites that are not taken up by either fluorine or hydrogen are filled by chlorine. For example, to determine the formula for Freon-12:
CFC -12 ---> 12+ 90 = 102
This implies:
1 Carbon
0 Hydrogen
2
To determine the number of chlorine atoms, begin by imagining the methane building block.
Then, using the numbers from the formula above, fill in the information that is derived. Finally, count the number of vacant sites. This number equals the number of chlorine atoms. In the case of CFC-12, 1 carbon has four bonding sites. Since there are 0 hydrogen and 2 fluorines, this leaves 2 bonding sites (4 carbon - 2 fluorines). Chlorines fill the empty sites meaning there are two chlorines.
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