Rotational Isomerism as a General Property of Alkyl Nitrites

Abstract

The infrared and ultraviolet spectra of 15 alkyl nitrites were studied in the gaseous state. In the infrared, the O–N=O group is characterized by very strong absorption in the three regions 600, 800, and 1650 cm−1, corresponding to O–N=O bending, N–O stretching, and N=O stretching frequencies, respectively. The doubling of the characteristic frequencies and the temperature dependence of the bands of methyl nitrite are explained by rotational isomerism, which appears to be a general property of alkyl nitrites. The influence of the length, shape, and kind of the carbon chain on the frequencies and intensities of the characteristic bands has been studied. The intensity variation of the νN=O bands strongly suggests that the relative abundances of the two isomers vary widely from primary to secondary and tertiary nitrites, but depend only to a small extent upon the length and shape of the carbon chain. Application of this property to the diagnosis of primary, secondary, or tertiary alcohols is suggested. The uv spectra consist essentially of two systems of diffuse bands (and not of one, as stated by previous workers), whose relative intensities vary in the same manner as the relative abundances of the two rotational isomers. The two systems of bands are accordingly assigned to these rotational isomers. This hypothesis has been checked by a study of the temperature dependence of the intensity of the bands.