Lactams: group frequencies

Carbonyl group frequencies for quinuclidin-2-ones are on the average 80 cm-1 higher than for common lactams, and integral intensities of the same absorptions are nearly half those of quinuclidin-2-ones. Ultraviolet (UV) absorption maxima for quinuclidin-2-ones are midway between those for amides and ketones. On account of the lack of amide mesomerism quinuclidin-2-ones gain in reactivity. This is shown by the rather high rates of hydrolysis of such compounds... 

Characteristic group frequencies of lactams are shown in Figure 39. As in lactones, the size of the... 

Spectral Characteristics. The iafrared stretching frequency of the penicillin P-lactam carbonyl group normally occurs at relatively high frequencies (1770 1815 cm ) as compared to the absorptions for the secondary amide (1504-1695 cm ) and ester (1720-1780 cm ) carbonyl groups. 

One of tire distinguishing physical characteristics of the cephalosporins is the infrared stretching frequency of the /i-lactam carbonyl. This absorption occurs at higher frequencies (1770-1815 cm-1) than those of either normal secondary amides (1504-1695 cm-1) or ester carbonyl groups (1720-1780 cm-1). 

Coordination via the carboxylate group is consistent with the observation that esterification of this group decreases the rate enhancement by ca. 5 x 103. In addition, the IR spectra of copper(II) /3-lactam complexes show a decrease in the carboxylate carbonyl stretching frequency of... 

Copper(II) binds some 10-fold more strongly to cephalosporins than to penicillins.411,414 Molecular models indicate that one of the conformations of cephalosporins would be very suitable for binding via the carboxylate group and the /8-lactam carbonyl oxygen (124) giving rise to a seven-membered chelate ring. Variations in the /3-lactam carbonyl stretching frequency on com-plexation provide some support for structure (124). 

Chromic acid oxidation of aspidospermine gave three lactams (XI, XII, and XIII, 24). The IR-carbonyl frequency (1680 cm-1) of the new amide group in lactam XI shows it to be in a five-membered ring, while the presence in the NMR-spectrum of a nonequivalence quartet at 2.37 ... 

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