Effects of Isomerism on Infrared Absorption Spectra

The absorption spectra of four organic cyanides, two organic thiocyanates, and the corresponding isomers have been studied in the region from 1.0μ to 6.5μ. The intense band appearing near 4.4μ in the normal cyanides appears at a longer wave-length and with doubled intensity in the isocyanides, the variation in wave-length and intensity being nearly constant for all compounds. In the case of the thiocyanates the variation in wave-length of the 4.6μ band for the two configurations is less than in the cyanides, whereas the intensity differences are greater. No other bands in these organic compounds were appreciably affected by isomerism. In the absorption spectrum of aqueous solutions of hydrocyanic gas there appears an intense band at 4.75μ and also a less intense band at 4.95μ. The band at 4.95μ can be attributed to a small amount of the isomer HNC.