Hexanoic Acid Infrared Spectrum

Figure 14.4. Infrared spectra showing common absorption bands. The —OH of acids and alcohols are hydrogen-bonded, leading to broadening.The —OH of hexanoic acid, which is unusually sharp, absorbs in the 3500-2500 cm-1 region. Bottom spectrum shows absorptions due to functional groups in the compounds making up the mixture.

Figure 14.6. Infrared spectra of a KBr pellet of 3% sodium humate (Aldrich) and an NMR spectrum of a mixture of toluene, hexanoic acid, and octanal. The functionalities responsible for the absorption features are labeled. 

Infrared spectrum of hexanoic acid. Carboxylic acids show a broad O — H absorption from about 2500 to 3500 cm-1. This broad absorption gives the entire C—H stretching region a broad appearance, punctuated by sharper C — H stretching absorptions. 

A student has just added ammonia to hexanoic acid and has begun to heat the mixture when he is called away to the telephone. After a long telephone conversation, he returns to find that the mixture has overheated and turned black. He distills the volatile components and recrystallizes the solid residue. Among the components he isolates are compounds A (a liquid molecular formula CgHnN) and B (a solid molecular formula C6H13NO). The infrared spectrum of A shows a strong, sharp absorption at 2247 cm-1. The infrared spectrum of B shows absorptions at 3390, 3200, and 1665 cm-1. Determine the structures of compounds A and B. 

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