Question

Where do primary amines appear in the IR spectrum?

a) 1700-1600 cm⁻¹
b) 3300-3000 cm⁻¹
c) 1600-1500 cm⁻¹
d) 3100-2800 cm⁻¹

Answer 1

Primary amines appear in the IR spectrum in the range of 3300-3000 cm⁻¹, which corresponds to the N-H bond stretching vibrations.

Step-by-step explanation:

The question asks about the infrared (IR) spectrum absorption range of primary amines. Primary amines are characterized by the N-H stretch vibrations in their IR spectra. These can be identified by two different types of bands in the IR spectrum: one due to symmetric stretching and another due to asymmetric stretching of the N-H bond. Primary amines typically exhibit these absorption bands in the region of 3300-3000 cm⁻¹. Therefore, the correct answer is b) 3300-3000 cm⁻⁹. This absorption is because of the N-H bond stretching vibrations present in primary amines. This absorption range is different from the absorption of alkynes, which have characteristic IR absorbance peaks in the range of 2100-2250 cm¹ due to stretching of the carbon-carbon triple bond, and terminal alkenes, which can be identified by their absorbance at about 3300 cm-1 due to stretching of the bond between the sp-hybridized carbon and the terminal hydrogen.