Análise Espectral de Compostos

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absorption at 1683 cm⁻¹ is due to a carbonyl group. The absence of bands for other carbonyl containing functional groups indicates that the compound is a ketone or an ester. It is often difficult to determine with certainty whether a compound is a ketone or an ester based solely on its IR spectrum. In this case there is a strong band near 1250 cm⁻¹, but it is not as broad as the C-O band of an ester normally appears. (See the spectrum in part (d) of this problem for an example of a spectrum of an ester.) Note that the carbonyl group of a conjugated ketone should appear at 1695-1675 cm⁻¹ whereas that of a conjugated ester should appear at 1720-1700 cm⁻¹. This compound is actually a conjugated ketone. d) The absorptions in the region of 3100-3000 cm⁻¹ are due sp²-hybridized C-H bonds, and those in the region of 3000-2850 cm⁻¹ are due to sp³- hybridized C-H bonds. The appearance of four bands in the 1600-1450 cm⁻¹ region and the strong band near 700 cm⁻¹ suggests the presence of an aromatic ring. The strong absorption at 1715 cm⁻¹ is due to a carbonyl group. The strong C-O band near 1200 cm⁻¹ indicates that the compound is an ester. The observed shift of the carbonyl band to a lower wavenumber is consistent with a conjugated ester. 13.15 a) The terminal alkyne (at the right) will have a sharp band at 3300 cm⁻¹ due to the =C-H group. Both will have peaks in the 2150-2100 cm⁻¹ region due to the C=C group, but the band from the terminal alkyne will be more intense because it is less symmetrical. b) The conjugated aldehyde (at the left) will have the absorption for its C=O group at lower wavenumbers (1710-1690 cm⁻¹) than the non- conjugated aldehyde (1730 cm⁻¹). c) The amine will have two bands in the 3400-3250 cm⁻¹ region. These bands will be of weaker intensity and less broad than the OH band of the alcohol, which will appear in the 3550-3200 cm⁻¹ region. d) The ester will show a band for its C=O group near 1740 cm⁻¹, whereas that for the ketone will appear near 1715 cm⁻¹. In addition, the ester will have a intense band for the C-O group in the 1300-1000 cm⁻¹ region. e) The alcohol will show a broad absorption for its OH group in the region of 3550-3200 cm⁻¹. The absorption for the OH group of the carboxylic acid will be broader than that for the alcohol and will be centered near 3000 cm⁻¹. In addition, the carboxylic acid will have an absorption for its C=O group near 1710 cm⁻¹. f) The ether will have an intense band in the 1300-1000 cm⁻¹ region due to the C-O bond. 208