Carbonyl doublet

Fourier transform infrared spectroscopy (FTIR) was also used to study the anisotropic structure of polyimide films. This work was based on the fact that there are characteristic absorptions associated with in-plane and out-of-plane vibrations of some functional groups, such as the carbonyl doublet absorption bands at 1700-1800 cm . The origin of this doublet has been attributed to the in-phase (symmetrical stretching) and out-of-phase (asymmetrical stretching) coupled... 

Infrared analysis (neat, film) shows a carbonyl doublet at 1740, 1770 cm 1, typical of 4-substituted benzoyl chlorides and thought to be due to Fermi resonance.2,3 Contamination of the product with the anhydride can be detected by a doublet at 1720 and 1780 cm 1, with the ketone by a singlet at 1650 cm 1, and with the acid by a singlet at 1690 cm 1. 

Irradiation of 2,2,4,4-tetramethylcyclobutane-I,3-dione in pentane, cyclohexane or dichloro-methane resulted in rapid evolution of carbon monoxide (0 = 0.30) and formation of 2,2,3,3-tetramethylcyclopropanone (1). The reaction was easily monitored by infrared spectroscopy, the photolysis was terminated when the characteristic carbonyl doublet of the cyclo-propanone (1823 and 1843 cm ) reached a constant intensity (10-20% conversion of cyclo-butane-1,3-dione). 

In most cases the frequencies of substituent groups attached to these heterocycles differ little from those observed for their benzenoid counterparts. The only notable exception is the spectral behaviour of carbonyl groups attached to position 2. These have attracted much attention as they frequently give rise to doublets, and occasionally multiplets. In the case of (34), (35) (76JCS(P2)l) and (36) (76JCS(P2)597) the doublets arise from the presence of two conformers (cf. Section 3.01.5.2), whereas for the aldehydes (37) the doublets are... 

IR spectroscopy has been particularly helpful in detecting the presence of keto tautomers of the hydroxy heterocycles discussed in Section 3.01.6. Some typical frequencies for such compounds are indicated in Figure 4. Here again the doublets observed for some of the carbonyl stretching frequencies have been ascribed to Fermi resonance. 

Complexes 41 and 42 were characterized by their IR and H-NMR spectra, and 41 also by elemental analysis. Table III contains the pertinent spectral data. Noteworthy are the very low energy terminal carbonyl bands for 41 and 42 at 1864 cm-1 (hexane). The weak 7r-accepting abilities of PR3 (R = Et, Ph) allow the lone CO ligand to 77-backbond to the Ti(II) center to a much greater degree. The -NMR spectrum of 41 exhibited a doublet (/H-p = 1.5 Hz) at 8 4.75 due to the coupling of the cyclo-pentadienyl protons with the 31P nucleus, while complex 42 exhibited a broad cyclopentadienyl singlet at 8 4.67. 

Monocarbonyl 44 exhibited a doublet (2H-p = 3.5 Hz) at 84.59 in its 1H-NMR spectrum, assignable to the cyclopentadienyl protons coupled with the 31P nucleus. Its IR spectrum displayed a strong metal carbonyl band at 1932 cm-1, while the mass spectrum showed a parent ion at... 

The low temperature 13C NMR spectrum of Rh CO), which is iso-structural with Co4(CO)i2 in the solid state, has three equally intense doublets due to the apical, axial, equatorial carbonyls and a triplet due to bridging carbonyls91. These multiplets arise through spin-spin coupling to 103 Rh (100% abundant,... 

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