Infrared absorption 3-lactam

Ultraviolet absorptions ofvinylogous lactams were found by MOLCAO calculations and compared with experimental values (663). Infrared spectroscopic studies of vinylogous amides (664) and some fifty vinylogous urethanes (665) allowed configurational and structural assignments. The effect of enamine-imine equilibrium in a series of benzophenone derivatives was established (666) and the effect of structure on enamine basicity studied (667). 

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. 

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). 

O-H bond. Among such properties a prominent one is the ultraviolet absorption spectrum and the theory may therefore be used for the examination of some of the spectroscopic shifts which accompany the lactam-lactim tautomerization. Much caution must, however, be exercised in this respect. Thus, in a recent paper Kwiatkowski135,137 performed Pariser-Parr-Pople-type calculations on the electronic structure of hydroxypurines, essentially to interpret their ultraviolet spectra. In these calculations he assumed that these compounds exist predominantly in their lactim form, and the results of his calculations, at least for 6- and 8-hydroxypurine, did not seem to contradict this assumption. It is only in the case of the 2-hydroxy isomer that a particularly striking disagreement between theory and experiment led him to admit that this last compound may exist in the lactam form. Calculations carried out for this form gave, in fact, a more satisfactory agreement with experiment.138 As we have seen, unambiguous infrared spectroscopy evidence clearly show s that all three isomers exist essentially in the lactam form. This shows that ultraviolet absorption may provide only very uncertain evidence about the lactam-lactim tautomerism in hydroxypurines and related compounds. 

Diaryl- and 2,5,6-triaryl-477-l,3,4-oxadiazines are stable solids which absorb at 3400, 1600-1590 and 1280-1250 cm-1 in the infrared.34,35 The l,3,4-oxadiazin-2-ones 2 are lactones their IR spectra show NH and carbonyl bands at ca. 3420 and 1730 cm-1, respectively.36 l,3,4-Oxadiazin-5-ones 3 are (5-lactams with vmax 1710-1700 cm-1 and 1,3,4-oxadiazin-6-ones 4 are acidic they exhibit <5-lactone carbonyl absorption at ca. 1800 cm-1. 

An interesting series of degradation products has been reported recently by Muller et al. (356). In addition to allocolchicine and some recovered starting material, a desacetylthiocolchicine, CjoH23N04S, has been obtained from the action of sodium methyl mercaptide on methylthiocolchicide. This substance was optically active and showed an ultraviolet absorption spectrum that was different from that of methylthiocolchicide. The infrared spectrum showed carbonyl absorption at 5.93 fi. This was interpreted by the authors as indicative of a y-lactam, and desacetylthiocolchicine was assigned the tentative structure CXII. 

Aside fixtm offering proof of the 6-hydroxyl group, these oxo compounds are examples of a widely sought structural unit. They are lactams derived from l-azabicyclo[3,2,l]octane. By Bredt s Rule, resonance interaction between the free electron pair of the nitrogen and the carbonyl group should be at a minimum. As a consequence, the compounds should behave as amino ketones rather than lactams. To a considerable extent, this expectation has been verified. The carbonyl absorption in the infrared more nearly resembles 6,7-methylenedioxy-... 

The infrared spectra of a series of IH-, 2H-, and 6//-1,4-diazepines all show C=N absorptions in the range 1615-1640 cm <87CPB3175, 87CPBH79, 90CPB29ii>. The amide carbonyl of 1-ethoxy-carbonyl l,4-diazepin-5-one is observed at 1674 cm which is within the range expected for a cyclic lactam. 2,3-Dihydro-1,4-diazepines do not exhibit a normal C=N absorption characteristic N—H bands are found between 3150 and 3190 cm <65CB270l>. The infrared spectra of 2,3-dihydro-diazepinium salts are more complicated than those of the free bases and have been reviewed <93AHC(56)1>. 

Because of the cyclic structure the NH and C=0 groups are forced into the cis configuration so that no band comparable to the amide 11 band in trans secondary amides occurs in lactams. A characteristically strong NH stretching absorption near 3200 cm occurs in the infrared, which is only weak to medium in the Raman. A weaker infrared band near 3100 cm" is due to a combination band of the C=0 stretching and NH bending vibrations. 

Campbell s group synthesized the spiro-p- lactams 123 and 124 (Brem-ner et al., 1976a,b) by treatment of 109 and 111 with 2 equiv of phen-yllithium in THF at -78°C, followed by an excess of phosgene. Spi-roureido adduct 123 was isolated in 19% yield and displayed characteristic infrared (IR) absorptions at 1858 and 1800 cm. Trichloroethyl derivative 124 was prepared in 16% yield and furnished 125 upon deprotection. This acid was inactive against a range of organisms. 

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