Absorption Studies of the Vapors of the Three Isomeric Picolines in the Near Ultraviolet

Abstract

Studies of the near ultraviolet absorption spectra of α-, β-, and γ-picoline vapor have been made in low and medium dispersion. Conclusive evidence is found for two electronic transitions in the vicinities of 35500 and 38500 cm−1. The former transition is interpreted as an allowed A1—B2 transition resulting from the excitation of an sp2 nonbonding electron of the nitrogen atom into the first unfilled π-orbital of the ring. The latter transition is considered an allowed A1—B1 transition resulting from the excitation of a π ring electron. The A1—B2 system exhibits narrow headless bands similar to the first absorption bands in pyridine. It is of weak intensity comparable to that of the forbidden A1g—B2u transition in benzene. The A1—B1 system, which is much stronger, consists of broad diffuse bands. There is evidence that this system may be overlapped by another transition in β-picoline.