[4]Annulene. Comments on its infrared spectrum

Abstract

A photo-precursor (4) of [4]annulene (1) has been irradiated at 4–10 K in argon. The infrared spectrum of the photolysate shows two strong bands at 1240 cm −1 and 570 but, in contradiction to an earlier claim, one at 650 cm −1 is missing. The discrepancy between this and the earlier observation is explained, and comments on the infrared spectrum of 1 are made.