IR carbonyl absorption frequencies

TABLE 2. IR carbonyl absorption frequencies (CHCI3) and selected NMR chemical shifts (CDCI3) for A-alkoxy-A-chloroamides (R CON(Cl)OR ) and precursor hydroxamic esters... 

TABLE 11. IR carbonyl absorption frequencies for A,iV-dialkoxyamides ureas and carbamates (R ON(OR )COR ) and their precursor hydroxamic esters (R ONHCOR )... 

VI, obtained from stereospecific reactions of the corresponding optically active alcohol (11) with thionyl chloride, phosphorus pentachloride, etc., was not racemized under any of the reaction conditions. Monitoring the carbonyl absorption frequencies in the IR during these decarbonylations showed that the transformations II — III — IV took place during the conversion of V to racemic VI. Thus rearrangement or decomposition or both could be responsible for the racemization. 

Figure 9 A plot of the frequency of maximum IR carbonyl absorption against temperature for (A) copoly(ethylene/vinyl acetate) and (B) a blend containing 80 wt.% chlorinated polyethylene and 20 wt.% copolymer. The shift is reduced at higher temperatures, which is attributed to a dissociation of the specific interaction between the polymers...

The most informative feature of the IR spectra of azetidin-2-ones is generally the /3-lactam carbonyl absorption, the frequency of which is affected by substitution and by fusion of the ring (c/. Table 3). Thus, IR spectra of simple monocyclic /3-lactams generally have absorption maxima in the region 1730-1760 cm while the fused 2- and 3-cephem systems (60) and (61) show IR maxima in the regions 1772-1784 and 1782-1792 cm S respectively (b-72MI50900 p. 318). 

IR spectra of systems related to /3-lactams show the expected trends in the frequency of the carbonyl absorption, where present. For example, the presence of an exocyclic double bond at C-4 in an azetidin-2-one raises the value of vc=o considerably. Thus the 4-thioxoazetidin-2-one (62 Z=S) and the derived 4-alkylidene systems (62 Z = CR R ) exhibit /3-lactam carbonyl absorptions at 1835 and 1800-1810 cm respectively (80JOC1477, 80JOC1481), while the 4-iminoazetidin-2-ones (63) have vc=o at 1800-1825 cm (81CC41). Additional spectral data for these and similar systems may be found in the references in Table 5. 

The role of IR spectroscopy in the early penicillin structure studies has been described (B-49MI51103) and the results of more recent work have been summarized (B-72MI51101). The most noteworthy aspect of a penicillin IR spectrum is the stretching frequency of the /3-lactam carbonyl, which comes at approximately 1780 cm" This is in contrast to a linear tertiary amide which absorbs at approximately 1650 cm and a /3-lactam which is not fused to another ring (e.g. benzyldethiopenicillin), which absorbs at approximately 1740 cm (the exact absorption frequency will, of course, depend upon the specific compound and technique of spectrum determination). The /3-lactam carbonyl absorptions of penicillin sulfoxides and sulfones occur at approximately 1805 and 1810 cm respectively. The high absorption frequency of the penicillin /3-lactam carbonyl is interpreted in terms of the increased double bond character of that bond as a consequence of decreased amide resonance, as discussed in the X-ray crystallographic section. Other aspects of the penicillin IR spectrum, e.g. the side chain amide absorptions at approximately 1680 and 1510 cm and the carboxylate absorption at approximately 1610 cm are as expected. 

Table 3.1 Carbonyl (C=0) IR Absorption Frequencies in Common Functional Groups...

The kinetics of hydrogenolysis of a metal-alkyl have been monitored by HP IR spectroscopy for [MeIr(CO)2l3] , the resting state in the cycle for iridium catalysed methanol carbonylation [113]. On treatment with H2 at elevated temperatures, the v(CO) bands of [MeIr(CO)2l3] decayed and were replaced by new r(CO) bands at slightly higher frequency and a v(Ir-H) absorption, corresponding to Eq. (10). 

Carbonyl stretching frequencies of sydnones occur over a wide range, from 1720 to 1790 cm . 3-Phenylsydnone has an IR absorption frequency for the exocyclic carbonyl group of 1757 cm values for other 3-arylsydnones obey a modified Hammett equation (95Mi 403-01 >. Sydnones show a single maximum in the UV spectrum close to 300 nm. 

The molecular symmetry of octahydropyridazino[ 1,2-a ]pyridazine (24) has been analyzed using band numbers, frequency coincidences and Raman depolarization factors in the IR and Raman spectra. A centrosymmetric trans conformation was confirmed for this compound (76SA(A)157). IR spectral data also indicate that the carbonyl absorption for pyridazino[l,2-a]pyridazine-l,4-diones (26) occurs at ca. 1625 cm-1 (72TL1885). 

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