Benzene rings spectral characteristics

The pyrones and thiinones show general 13C NMR spectral characteristics similar to the pyridones which reflect charge distributions in the heterocyclic rings. Thus, carbon atoms a or y to the heteroatom are deshielded relative to benzene, while those (3 are shielded. Substituent effects are in general as expected, although fewer detailed studies have been carried out in this area with the oxygen and sulfur heterocycles than with the azines. Chemical shift data for representative compounds are given in Scheme 10. 

The most significant feature of the spectrum shown is the strong C=0 stretch at 1688 cm which is characteristic of aromatic carbonyl compounds (simple saturated carbonyl compounds have a C=0 stretch at about 1720 cm M The presence of a benzene ring can be confirmed by the moderate to strong bands at 1601/ 1585, 1500 and 1450 cm". These absorptions are characteristic of the C=C stretch of benzene derivatives. Further spectral evidence supporting the hypothesis of a carbonyl functionality can be seen by the two weak bands at 2750 cm" and 2820 cm . These absorptions are characteristic of the C-H stretch of aldehydes. Another important feature of this spectrum is the moderate band at 1050 cm which is the typical absorption of the C-0 stretch of ethers. We now know that compound P is an aromatic aldehyde with a possible ether linkage. 

Fig. 71 Polystyrene the changes in resistance to deformation (a), energetic state (AH) and IR spectral characteristics as a function of pre-straining on compression at 20°C [15] (1) the stress-strain curve for annealed samples (2) ditto for quenched samples (3) enthalpy increment AH (DSC) (4) the extinction coefficient i602 of the IR band of deformation vibrations of the benzene rings at 1,602cm" as a measure of universal IMI (5) increment in mechanical loss (internal friction) A5ip (6) the ratio of optical densities of the IR bands at 560 and 542 cm" as a criteria of changes in the conformational composition...

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