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13.22 The DU of this compound is 1. The peak at 1741 cm⁻¹ is due to the presence of a C=O, which accounts for the DU. The position of the C=O peak, along with the intense peak near 1250 cm⁻¹, suggests that the unknown is a saturated ester. Butyl acetate is one possibility. 13.23 The DU of this compound is 3. The peaks in the 3000-2850 cm⁻¹ region show the presence of H's bonded to sp³-hybridized C's. There is no sign of H's bonded to sp²-hybridized C's. The peak near 2250 cm⁻¹ suggests the presence of a C=N group, which accounts for two degrees of unsaturation. The peak at 1740 cm⁻¹ is due to a C=O group and accounts for the other degree of unsaturation. The position of the C=O band and the N intense band near 1200 cm⁻¹ suggests that the unknown is an ester. One possibility is ethyl cyanoacetate. 13.24 The DU of this compound is 2. The peaks in the 3000-2850 cm⁻¹ region show the presence of H's bonded to sp³-hybridized C's. There is no sign of H's bonded to sp²-hybridized C's. The peak at 1718 cm⁻¹ indicates the presence of a C=O group. The absence of peaks expected for other carbonyl containing functional groups and the position of the C=O peak indicate that the unknown is a ketone. Because there is no evidence for the presence of a C=C, the second degree of unsaturation must be due to a ring. Cycloheptanone is one possibility for the unknown. 13.25 Th DU of this compound is 5. The peaks in the 3000-2850 cm⁻¹ region show the presence of H's bonded to sp³-hybridized C's. The small peaks in the region of 3100-3000 cm⁻¹ suggest the presence of H's bonded to sp²-hybridized C's. The two peaks in the 2830-2700 cm⁻¹ region, along with the C=O peak at 1706 cm⁻¹ indicate the presence of an aldehyde. The position for the C=O of the aldehyde suggests that it is conjugated. The bands in the 1600-1450 and 900-675 cm⁻¹ regions indicate the possible presence of an aromatic ring. Note that an aromatic H ring has a DU = 4, so the presence of an aromatic ring and a C=O would account of the DU of 5. One possible structure is 4-ethylbenzaldehyde. 210