Name that compound: The numbers game for CFCs, HFCs, HCFCs, and Halons
T.J. Blasing and Sonja Jones
Chlorofluorocarbons (CFCs) contain Carbon and some combination of Fluorine and Chlorine atoms.
Hydrofluorocarbons (HFCs) contain Hydrogen, Fluorine, and Carbon (no chlorine).
Hydrochlorofluorocarbons (HCFCs) contain Hydrogen, Chlorine, Fluorine, and Carbon atoms.
Hydrobromofluorocarbons (HBFCs) contain Hydrogen, Bromine, Fluorine, and Carbon atoms.
Perfluorocarbons contain Fluorine, Carbon, and Bromine atoms, and some contain Chlorine and/or Hydrogen atoms.
These compounds are often designated by a combination of letters and numbers (e.g., CFC-11, HCFC-142b).
In the latter example, the lower-case b refers to an isomer, which has no relationship to the chemical formula (C2H3F2Cl), but designates a particular structural arrangement of the atoms included. For example, HCFC-142b identifies the isomer in which all three hydrogen atoms are attached to the same carbon atom, and the structural formula is written as CH3CF2Cl. By contrast, HCFC-142 (without the b) refers to an arrangement in which one carbon atom is attached to two hydrogen atoms and one chlorine atom, while the other carbon atom is attached to the third hydrogen atom and two fluorine atoms. Hence, it has a different structural formula (CH2ClCHF2).
To find the number, given the chemical formula: consider the number as consisting of 3 digits: a, b, and c. For 2-digit numbers (e.g., CFC-11) the a digit is zero (e.g., CFC-011).
a is the number of carbon atoms minus 1;
b is the number of hydrogen atoms plus 1;
c is the number of fluorine atoms.
|For CFCl3:||a||=||the number of carbon atoms (1) minus 1||=||0|
|b||=||the number of hydrogen atoms (0) plus 1||=||1|
|c||=||the number of fluorine atoms||=||1|
and, the compound is CFC-011, or CFC-11.
- CCl2F2 is CFC-12
- C2Cl3F3 is CFC-113
To find the chemical formula, given the number: first add 90 to the abc number, to obtain a 3-digit def number, where:
- d is the number of carbon atoms;
- e is the number of hydrogen atoms;
- f is the number of fluorine atoms; and
- 2d + 2 - e - f = the number of chlorine atoms.
For CFC-11: 90 + 11 = 101, so the number of carbon atoms is 1, the number of hydrogen atoms is zero, the number of fluorine atoms is 1, and the number of chlorine atoms is (2 + 2 - 0 - 1 = 3).
So the chemical formula for CFC-11 is CFCl3. That is, it has 1 carbon atom, no hydrogen, 1 fluorine atom, and 3 chlorine atoms.
|Similarly:||CFC-12: 12 + 90 = 102; 4-2 = 2 Cl; the chemical formula is:||CCl2F2|
|CFC-113: 113 + 90 = 203; 6-3 = 3 Cl; the chemical formula is:||C2Cl3F3|
|HCFC-142b: 142 + 90 = 232; 6-5 = 1 Cl; the chemical formula is:||C2H3F2Cl|
Halons are fluorocarbons (not hydrofluorocarbons, i.e., no hydrogen atoms) with at least one bromine atom.
Halon (no hydrogen number) nomenclature is relatively simple; each halon has an abcd number, where:
|a||=||the number of carbon atoms;|
|b||=||the number of fluorine atoms;|
|c||=||the number of chlorine atoms, and|
|d||=||the number of bromine atoms.|
C2F4Br2 is Halon 2402.
And, an example going the other way:
Halon 1211 is CF2ClBr.
Acknowledgement: Thanks to Jack Calvert, Environmental Sciences Division, Oak Ridge National Laboratory, for a constructive review of this work which added substantially to its content.