Electronic Properties of N-Heteroaromatics. XLVII. Absorption Spetra and Electronic Structure of Some Quinoline 1-Oxides of Biological Interest

Abstract

Near-ultraviolet and visible absorption spectra of quinoline 1-oxides in aqueous and nonaqueous solutions were measured, with emphasis on 10 kinds of compounds known to be carcinogenic or non-carcinogenic, and the absorption bands were classified according to Platt's nomenclature system. Absorption spectra of 4-nitroquinoline 1-oxide and its derivatives in nonaqueous solution were separately assigned to the ¹L_b and ¹L_a bands, in addition to ¹B_b band. Molecular orbitals of quinoline 1-oxides were calculated by the simple LCAO-MO method. From the energy difference between molecular orbitals, each of the absorption bands was assigned to the electronic transition between specified molecular orbitals. The following relationship between band assignment and electronic transition was found for 4-nitroquinoline 1-oxide and its 2-methyl, 6-chloro, 6-carboxy, and 6-nitro derivatives : ¹L_b band, ψ_m→ψ_m+1 ; ¹L_a band, ψ_m-1→ψ_m+1 ; ¹B_b band, ψ_m→ψ_m+2 ; ¹B_a band (for 6-nitro derivative), ψ_m-1→ψ_m+2.