13.8 : 红外频率范围：X-H 伸缩

Single or X–H bonds like C−H, O−H, and N−H give rise to absorption bands in the frequency range of 2850–3600 cm^–1 in the diagnostic region of the IR spectrum.

C–H stretching peaks between 2850–3000 cm^–1 exhibit multiple splitting and are strongly observed in alkanes.

Although N–H and O–H absorption regions overlap, their respective shapes distinguish their peaks.

N–H stretching vibrations appear as one or two sharp bands of lower intensity in the range of 3300–3500 cm^–1. For instance, primary amines, like 1-butanamine, exhibit two sharp lower intensity peaks because of symmetric and asymmetric N–H stretching.

O–H peaks corresponding to hydrogen-bonded O–H are broader and appear in the frequency range of 3200–3500 cm^–1. In contrast, those not participating in hydrogen bonding are narrow and appear near 3600 cm⁻¹.

Overall, the O–H stretching vibrations are more intense in nature as they are accompanied by a greater change in dipole moment.