AbstractInfrared spectra are reported for CH3SCN and CH3NCS from 170–3100 cm−1 for both liquid and vapor states. The Raman spectrum of CH3NCS has been re‐determined. A vibrational assignment is suggested for each molecule which is complete except for the methyl torsional frequencies.A useful qualitative means of distinguishing organic thiocyanates from isothiocyanates is the infrared absorption near 2150 cm−1. In thiocyanates this is a strong, relatively sharp band, whereas in isothiocyanates it is a strong, very broad absorption which is usually resolvable into 2–3 maxima. The origins of the latter are discussed.