The infrared spectra of six 1-(2-thienyl)-3-thiaalkanes and seven 1-(2-thienyl)-4-thiaalkanes (molecular weights from 186 to 270) were obtained for the 4000 to 400 cm−1 range. These spectra are compared with spectra of other thiophene ring compounds substituted in the 2-position for their characteristic absorption bands. The spectra agree with other spectra as to the major absorption band around 680 cm−1 and the 2-substitution overtone pattern. A method of distinguishing between the two groups of compounds from moderate peaks in the 600 to 500 cm−1 (KBr) region is shown. Interference from the 2-alkylthiophenes and the 1-(2-thienyl)-1-thiaalkanes does not occur.