Hydroxy acids electronic spectra

Fig. 3.1.10 Electron-impact mass spectrum of an unknown compound tentatively identified by GC-MS-MS as 4-hydroxy 2-hexenoic acid...

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). ... 

Photochemical transformations of the hydroxy-substituted amino acids serine 1 and threonine have been described, and mechanistic outHnes based on an electron or a hydrogen transfer key-step have been discussed. The broad spectrum of photoproducts obtained from the C-unprotected serine derivative 1 originated from both reactive sites of the molecule the carboxyl and the hydroxy group (Scheme 1 Table 84.1). Product 4 derived from primary a-photodecarboxylation, and further 5-elimination led to the olefinic compound 2. N-Methylphthalimide 3 was formed via initial extrusion of formaldehyde foUowed by rapid a-photodecarboxylation vide infra). When this a-photodecarboxylation site was blocked, as for the corresponding methyl ester, solely retro-Aldol cleavage occurred. Although azomethine... 

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