Lactones infrared frequencies

The typical infrared (IR) peaks are also shown for some important structural features in oxazines 1779cm for the lactone C=0 in 100, 1663 cm for the lactam C=0 in 104, and 1640 cm for the C=N of 2//-oxazines 46 and 47. In 103, the observation of the NH absorption at 3311 cm was used to establish the presence of this tautomeric form (see Section 8.06.4.2), and adding deuterium oxide changed the absorption to the lower frequency of 2475cm characteristic of an N-D bond. 

The infrared spectra of gibberellic acid and derivatives which all show absorption at ca. 1780 cm. 1 in solution, too high a frequency for the 8-lactone of the Japanese structure. 

The carbonyl frequency in the infrared spectrum provides a fairly characteristic method for differentiating between 1,4- and 1,5-lactones of aldonic acids. With few exceptions, the absorptions are in the range 1790-1765 and 1760 to 1725 cm-1, respectively.69 Configurational and conformational conclusions have been drawn from H and 13C NMR spectroscopy of aldonic acids and aldonolactones, using different correlation methods, enriched compounds, and shift reagents. For example, the solution conformation of aldono-1,4-lactones enriched with 13C at C-l have been determined on the basis of the coupling constants (homo and heteronuclear). In general, 0-2 is oriented quasi-equatorially due to stereoelectronic factors.36 Similar conclusions were made by Horton and Walaszek, who described the conformation of pentono- 1,4-lactones as an equilibrium between the 3E and forms.70 Conformations of D-hexono-1,4-lactones in solution have also been studied by NMR spectroscopy.70a The solution equilibrium of protected derivatives and their conformations have been described.71... 

Infrared (IR) spectroscopy is not characteristically definitive for the identification and structural proof of the dioxetane core. Dioxetanones 2 (a-peroxy lactones) such as 29 and 30, depicted in Section 2.16.3.1.4, show carbonyl stretching frequencies at 1835 and 1870cm-1, respectively <1997JOC1623, 1977JA5768>. 

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