Quinolizinium, cationic, electronic

Heteroaromatic compounds are isoconjugate with the corresponding aromatic hydrocarbons (the parent hydrocarbons). For example, the parent of quinolizinium cation (1) is naphthalene. The difference in the electronic energies between the heteroaromatic compound and the parent hydrocarbon can be expressed by first order perturbation theory as follows ... 

Differences between the absorption spectra of quinolizinium iodides and perchlorates reveal the presence of charge transfer bands believed to arise from electronic transitions from the iodide ion to either the solvent or the cation (60JCS2437). 

When the quinolizinium salt bears a very powerful electron-withdrawing group, ring opening can occur at low temperatures in aqueous acid. Such a group is the diazonium cation, and attempts to diazotize 1-aminoquino-lizinium salts led, via the ring-opened intermediate 196 to triazolo[l,5- ]-pyridines 197-199.133 170-171 jt js noteworthy that the Z double bond is retained in the side chain, and that the deuterium was fully retained when a [2,4-2H2]-l-amino-3-methylquinolizinium salt was treated with nitrous acid, giving compound 200. 

The pyrido[l,2-a]pyrazinium cation has been compared with the quinolizinium ion and the other monoazaquinolizinium cations, using the Pariser-Parr-Pople method to calculate electronic structures and absorption spectra. The ultraviolet spectrum of pyrido[l,2-a]pyrazinium bromide in water shows maxima at 232, 276, 287, 322, and 336 nm. Ultraviolet spectra have been recorded for various substituted compounds and their iV-oxides. The bands at 1685 and 1655 cm in the infrared spectrum (KBr disc) of the oxo compound 5 (R = H) confirm its formulation as the 0X0 form rather than as the corresponding hydroxy tautomer. Similarly the dioxo derivative 6 exists as such, in preference to the hydroxy form 5 (R = OH). The presence of a two-proton singlet at 6 6.1 in the PMR spectrum (in trifluoroacetic acid) of compound 6 is strong evidence in favor of this formulation. Ultraviolet spectral data are consistent with structures 6 and 5 (R = H). ... 

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