Chlorination of methane produces four basic chemicals: methyl chloride (CH3Cl), methylene chloride (CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4). When combinations with fluorine are considered, 13 methane derivatives are possible. This family of chlorofluoromethanes includes the major commercial compounds F-11 (CCl3F), F-12 (CCl2F2), F-21 (CHCl2F), and F-22 (CHClF2). When bromine and iodine substituents are considered the family of substituted methanes becomes much larger. The infrared spectra of all these compounds are strong and characteristic. There is no better way to measure them than by their infrared absorption. See SPECTRA, chap. P.