What Is Carboxylic Ir Spectrum? Easy Identification

The infrared (IR) spectrum of a carboxylic acid is a unique fingerprint that can be used to identify the presence of this functional group in a molecule. Carboxylic acids are characterized by a specific pattern of absorption bands in the IR spectrum, which can be used to distinguish them from other types of organic compounds.

One of the most distinctive features of the IR spectrum of a carboxylic acid is the presence of a broad, intense absorption band in the region of 2400-3400 cm-1, which is attributed to the O-H stretching vibration of the hydroxyl group. This band is typically broad and structured, with a maximum absorption intensity at around 2800-3000 cm-1.

In addition to the O-H stretching band, the IR spectrum of a carboxylic acid also typically shows a strong absorption band at around 1710-1780 cm-1, which is assigned to the C=O stretching vibration of the carbonyl group. This band is usually sharp and intense, and is often accompanied by a weaker absorption band at around 1200-1300 cm-1, which is attributed to the C-O stretching vibration.

Another characteristic feature of the IR spectrum of a carboxylic acid is the presence of a broad, weak absorption band in the region of 900-1200 cm-1, which is attributed to the C-O stretching vibration of the hydroxyl group. This band is often overlapped by other absorption bands, but can be useful in confirming the presence of a carboxylic acid functional group.

To illustrate the IR spectrum of a carboxylic acid, let’s consider the example of acetic acid (CH3COOH). The IR spectrum of acetic acid shows a broad, intense absorption band at around 2400-3400 cm-1, which is attributed to the O-H stretching vibration of the hydroxyl group. The spectrum also shows a strong absorption band at around 1715 cm-1, which is assigned to the C=O stretching vibration of the carbonyl group. Additionally, there is a weaker absorption band at around 1200 cm-1, which is attributed to the C-O stretching vibration of the hydroxyl group.

Here are some key points to keep in mind when identifying carboxylic acids using IR spectroscopy:

• Broad, intense absorption band at 2400-3400 cm-1 (O-H stretching)
• Strong absorption band at 1710-1780 cm-1 (C=O stretching)
• Weaker absorption band at 1200-1300 cm-1 (C-O stretching)
• Broad, weak absorption band at 900-1200 cm-1 (C-O stretching of hydroxyl group)

It’s also important to note that the IR spectrum of a carboxylic acid can be influenced by the presence of other functional groups, such as alkenyl or alkynyl groups, which can lead to the appearance of additional absorption bands in the spectrum.

In conclusion, the IR spectrum of a carboxylic acid is a powerful tool for identifying the presence of this functional group in a molecule. By analyzing the characteristic absorption bands, including the broad, intense O-H stretching band and the strong C=O stretching band, you can easily identify carboxylic acids and distinguish them from other types of organic compounds.