Alkyl and aryl halide infrared spectra

It is difficult to determine the presence of halides using IR, since they absorb at very low frequencies, in the fingerprint region. Mass spectroscopy is a much easier method.

C-F: Strong stretch at 1400-1000, polyfluoroalkanes give multiple bands.

C-Cl: Strong stretch in aliphatic chlorides occurs at 785-540. Primary chlorides absorb at the upper end, tertiary chlorides absorb near the lower end. Two or more bands may be observed. CH₂-Cl wagging is at 1300-1230.

C-Br: A strong stretch at 650-510. This is out of the range (650) for typical NaCl IR cells, but using more expensive KBr cells will extend the visible region down to 400, allowing this to be seen. The trend for aliphatic chlorides holds for bromides. Aryl bromides absorb at 1075 and 1030. CH₂-Br wagging is at 1250-1190.

C-I: A strong stretch at 500-485 for aliphatic iodides, out of the range of typical NaCl cells. Same trends for aliphatic iodides as aliphatic chlorides. CH₂-I wagging at 1200-1150.

Carbon tetrachloride

Chloroform