Carbonyl compounds infrared absorption

The 4-Hydroxy-thiazoles are characterized by infrared absorption near 1610 cm (KBr) (3) or 1620 to 16.S0cm (CCI4) (8), indicating a strongly polarized carbonyl group. H-5 resonates near 5.6 ppm in the NMR spectrum like similar protons in other mesoionic compounds (3). Two fragmentations of the molecular ion are observed in the mass spectra. The first involves rupture of the 1,2 and 3,4 bonds with loss of C2R 0S . In the second, the 1,5 and 3,4 bonds are cleaved with elimination of C2R 0. ... 

The CO stretch in the infrared spectra of carbonyl compounds gives rise to a strong absorption around 1700 cm , and is often used as a diagnostic. 

Table 21.3 Infrared Absorptions of Some Carbonyl Compounds...

There are at least two different series of isomeric compounds having the formula Pt4(C0)sL4. One series, which is brown-black (L = PMe2Ph50, PPh3 50 2S1, PPh2(o-Tol)251, PPh(o-Tol)2 251 ) and has only bridging carbonyl infrared absorptions, has the structure shown in Fig. 19. The other series of compounds, which are all red,... 

All these frequencies are in the region of other heteroaromatic compounds and of azulenes. Infrared absorption spectra for several derivatives of the following pseudoazulene systems have been reported 26,56 28,77 2985 86 33 96.uio 35,165 39,"3114 42, 23 49,135 136 and 56.143144-146 The key frequencies for substituents at positions 1 or 3 in the five-membered ring are shifted to lower wavelengths in a typical manner. This is especially pronounced in the case of carbonyl groups. 

The Infrared Region 515 12-4 Molecular Vibrations 516 12-5 IR-Active and IR-lnactive Vibrations 518 12-6 Measurement of the IR Spectrum 519 12-7 Infrared Spectroscopy of Hydrocarbons 522 12-8 Characteristic Absorptions of Alcohols and Amines 527 12-9 Characteristic Absorptions of Carbonyl Compounds 528 12-10 Characteristic Absorptions of C—N Bonds 533 12-11 Simplified Summary of IR Stretching Frequencies 535 12-12 Reading and Interpreting IR Spectra (Solved Problems) 537 12-13 Introduction to Mass Spectrometry 541 12-14 Determination of the Molecular Formula by Mass Spectrometry 545... 

Compound A is a cyclic, nonconjugated keto alkene whose carbonyl infrared absorption should occur at 1715 cm-. Compound B is an a,B-unsaturated, cyclic ketone additional conjugation with the phenyl ring should lower its IR absorption below 1685 cm-1. Because the actual IR absorption occurs at 1670 cm-1, B is the correct structure. 

The other compound, called Zl, which was much more acid-labile, was hydrolyzed to equimolar amounts of pyruvate and shikimate, and was tentatively assigned the structure of shikimate 3- or 5-enolpyruvate ether. In a more recent study, it was found that the barium salt of Zl does not absorb in the carbonyl region of the infrared absorption spectrum (no ester structure), and that it has a strong band at 8.2iu characteristic of a vinyl ether. It is oxidized very rapidly by periodate, giving rise to an unstable compound with maximum absorption at 235 m i ( = 4000). A similar unstable chromophore, most likely having the structure XVII, was produced by periodate oxidation of shikimate 3-phosphate but not of shikimate 5-phosphate. (3-Methyl-crotonaldehyde shows Xm 235, t = 6700. ) These observations suggest that Zl is shikimate 3-enolpyruvate ether (XVIII). 

The synthesis of the allyl ethers in nitrogen heterocyclic systems presents an element of complication in that the allylation could occur on the oxygen atom or the basic nitrogen atom. This is a feature of alkylation of ambident anions.3 However, this applies only when the allylation is effected by reacting the oxo or hydroxy derivative of the compound with an allyl halide in the presence of a base.3 The alternative method is to react the appropriate halo derivative with sodium allyloxide in allyl alcohol. The latter approach provides not only better yields of the allyl ethers but also certainty of the constitution of the ethers obtained. A diagnostic tool in deciding between the 1-allyl derivative and the O-allyl compound that has commonly been employed is the infrared absorption of the amide carbonyl in the case of the former which is clearly absent in the latter. 

---