The Double-Bond Region

If the carbonyl carbon is part of a five-membered ring, the position of the absorption band is increased by about 30 cm-1. 

1690-1630 (often has additional bands at slightly lower wavenumbers) 

Predict the position of the absorption band for the carbonyl group of this compound in its IR spectrum  

This compound is an ester, and the carbonyl group is conjugated with the aromatic ring. The predicted position is 1740 — (20 to 40) = 1720 to 1700 cm-1. 

Predict the positions of the absorption bands in the IR spectra for the carbonyl groups of these compounds. 

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The oxaziranes are colorless and they do not absorb in the UV region. Aryl-substituted oxaziranes show only the absorption of the aryl group. The oxaziranes are also transparent in the double bond region of the infrared spectrum, but they show a well developed band near 1400 cm" which has been considered characteristic for oxa-ziranes. ... 

The hydrazone structure 40 can be eliminated at once many examples of this class of compounds are known and their properties are completely different from the diaziridines. For example, 3,3-dimethyldiaziridine has a heat of combustion of about 35 kcal higher than the isomeric acetone hydrazone. Further pairs of isomers of diaziridines and hydrazones are known. The spectrum eliminates both the hydrazone structure and the betaine structure 41. The diaziridines do not absorb in the UV range. In the infrared spectrum, absorption is completely absent in the double-bond region. - The NMR spectrum of 3,3-dimethyldiaziridine is in agreement with a formulation that has two equivalent iV-protons. ... 

Firm assignments for these C=C bands require more detailed experiments but a tentative assignment can be made. The bands at 1550-1570 cm-1 are probably due to a ir-allyl species the shift from the double-bond region for butenes is about 100 cm-1 compared to the shift of 107 cm-1 observed for the 7r-allyl formed from propylene, but the butene is less firmly held. With propylene we observed a x-complex in which the shift in C=C stretch was about 30 cm-1. We believe the band at 1610 cm 1... 

The double bond region (2000-1500 cm 1), where in catalytic studies bridge-bonded CO, as well as carbonyl groups in adsorbed molecules (around 1700 cm 1), absorb,... 

The double bond region is the most important in IR spectra... 

The cream-colored ligand salt is soluble in acetone, nitromethane, and acetonitrile but insoluble in water and alcohols. The ligand salt is a biunivalent electrolyte in acetonitrile and nitromethane. The infrared spectrum of this material shows several characteristic bands a broad N—H stretcliing frequency at 3300 cm , a broad intense absorption in the double-bond region at 1600 cm, and bands due to hexafluorophosphate at 860 and 560 cm. The PMR spectrum in nitromethane shows five types of proton resonances as expected singlet methyl at 5 2.41, broad methylene at 5 3.83, doublet vinyl at 6 6.38 and 5 6.58, complex vinyl near 5 8.0, and broad NH at 6 7.6. 

This square planar nickel(ll) complex is stable in air in the solid state, but solutions of the complex react in air to produce oxidation products of unknown composition. For this reason, manipulations of the complex are best performed in an inert atmosphere. The complex is a nonelectrolyte and is soluble in most common organic solvents, including diethyl ether, but not in water. The infrared spectrum of the complex contains an intense broad band in the double-bond region centered at 1610 cm. The electronic spectrum of a solution of the compound in toluene contains several bands 17.9 (e = 107), 23.0 (e 1600), 24.5 (e 4600), 25.9 (e 2700), and 29.4 kK (e 5500). The PMR spectrum of the complex in CDCI3 contains four bands as expected singlet methyl at 5 1.88, methylene at 6 3.13, vinyl doublet at 6 4.51, and a second vinyl doublet at 5 6.63. The vinyl protons of the charged chelate ring are coupled, J = 3 Hz. 

On specifically examining a large number of thiazolidines in the double bond region down to 1470 cm only the carbonyl bond was revealed to be present ( 1748 and 1613 em ). 

Having this information, the chemist can proceed immediately to the double-bond regions of the infrared spectrum. There she finds evidence for a carbon-oxygen double bond (carbonyl group). At this point the number of possible isomers which might include the unknown has been narrowed considerably. Further analysis of the spectral evidence leads to an identification of the unknown substance as isopentyl acetate. 

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