In infrared (IR) spectroscopy, aldehydes are known to display distinctive absorption peaks in the ranges of $1720-1740 \, \text{cm}^{-1}$ and $2700-2800 \, \text{cm}^{-1}$.

IR spectroscopy serves as a powerful method for identifying functional groups in organic compounds, including aldehydes. The defining feature of aldehydes is the presence of a carbonyl group (C=O) coupled with a hydrogen atom attached to the same carbon atom. This unique structure results in specific absorption peaks within the IR spectrum.

The most prominent absorption peak for an aldehyde typically appears in the range of $1720-1740 \, \text{cm}^{-1}$. This peak is associated with the stretching vibration of the carbonyl group. Although the exact position of this peak may vary slightly based on the specific aldehyde structure and the presence of other functional groups, it is generally observed in this range. The peak is strong and sharp due to the high polarity of the carbonyl group.

In addition to the carbonyl peak, aldehydes also exhibit a characteristic pair of peaks within the $2700-2800 \, \text{cm}^{-1}$ range. These peaks arise from the C-H bond in the aldehyde functional group. The appearance of a pair of peaks is due to the different vibrational modes of the C-H bond, which can vibrate both symmetrically and asymmetrically. The symmetric vibration produces one peak, while the asymmetric vibration produces the other. Although these C-H peaks are typically weaker than the carbonyl peak, they remain important indicators of the presence of an aldehyde group.

It is crucial to note that while these peaks are characteristic of aldehydes, they are not exclusive to them. Other functional groups may also exhibit peaks in these regions. Therefore, the identification of an aldehyde in an IR spectrum should always be corroborated with additional evidence, such as the presence of other characteristic peaks or the application of complementary analytical techniques.