Which functional groups correspond to the characteristic peaks of the infrared spectrum of acetic acid?

Acetic acid infrared spectrum characteristic peak corresponding to which functional groups?

Infrared spectroscopy (IR) is an effective tool for the analysis of functional groups in compounds. As a common organic compound, the infrared spectrum of acetic acid has unique characteristic peaks, which can clearly reflect the characteristics of its functional groups. In this paper, the main characteristic peaks in the infrared spectrum of acetic acid and their corresponding functional groups will be analyzed in detail.

1. Acetic acid structure and main functional groups

Acetic acid (CH3COOH) is a carboxylic acid with a carboxyl (-COOH) functional group in its molecular structure. The basic structure of carboxylic acids includes a carbonyl group (C = O) and a hydroxyl group (-OH), which have significant characteristic absorption peaks in the infrared spectrum. The acetic acid molecule also contains the stretching vibration of methoxy (C-O), which is also an important characteristic peak in the infrared spectrum.

2. Acetic acid infrared spectrum in the O-H stretching vibration peak

In the infrared spectrum of acetic acid, hydroxyl (-OH) stretching vibration is a significant characteristic peak. The O-H bond of the hydroxyl group typically exhibits a strong absorption peak in the wavenumber range of 2500-3500 cm¹. Since the hydroxyl group in acetic acid is an acidic hydroxyl group, the frequency of the stretching vibration of its O-H bond is slightly lower than the O-H bond of ordinary alcohols, and it usually appears in the region of about 2600-2750 cms¹. The bending vibration of the hydroxyl group will also appear in the wave number range of 1400-1600 cm¹, but its intensity is weak relative to the stretching vibration.

The stretching vibration peak of the O-H bond usually shows a broad and strong absorption band in the infrared spectrum, which is mainly caused by the hydrogen bonding effect of the hydroxyl group. In the acetic acid molecule, the hydrogen bond of the hydroxyl group will shift its absorption peak to a lower wave number, because the formation of the hydrogen bond leads to the weakening of the strength of the O-H bond and the decrease of the vibration frequency.

3. Acetic acid infrared spectrum in the C = O stretching vibration peak

Another important characteristic peak is the stretching vibration peak of carbonyl group (C = O). In the infrared spectrum of acetic acid, the stretching vibration of the C = O bond usually appears in the wave number range of 1700-1850 cm¹. Specifically, the carbonyl absorption peak of carboxylic acids is generally between 1700-1730 cm¹. The absorption peak intensity in this region is higher and the peak shape is sharper.

The wave number position of the stretching vibration peak of the C = O bond is mainly determined by its electronic environment. In carboxylic acids, the electronic environment of the carbonyl group is affected by the adjacent hydroxyl group, which makes the electron cloud density of the C = O bond increase, which leads to its vibration frequency slightly lower than that of the C = O bond of the ketone compound. The absorption peak of the carbonyl group is usually accompanied by some deformation vibrations in the infrared spectrum, such as the asymmetric and symmetric stretching vibrations of the C- O, which usually appear in the region of 1250-1400 cms¹.

4. Acetic acid infrared spectrum in the C- O stretching vibration peak

In addition to the C = O and O-H bond stretching vibration, the C- O bond stretching vibration in the acetic acid molecule is also an important characteristic peak. The absorption peak of the C- O bond usually occurs in the wave number range of 1250-1350 cms¹. Since the C- O bond is a medium-strength bond, the intensity of its absorption peak is weaker than that of the C = O and O-H bonds.

The wave number position of the stretching vibration peak of the C- O bond is mainly affected by other functional groups in the molecular structure. In acetic acid, the absorption peak of the C- O bond usually interacts with the absorption peaks of the C = O and O-H bonds, resulting in a certain change in the peak shape. The stretching vibrational peak of the C- O bond may be affected by the intermolecular hydrogen bond, which causes a slight shift in its wave number position.

5. Application of Infrared Spectroscopy in Acetic Acid Structure Analysis

By analyzing the infrared spectrum of acetic acid, the main functional groups can be clearly identified, including hydroxyl (-OH), carbonyl (C = O) and methoxy (C-O). The presence of these characteristic peaks can not only confirm the identity of acetic acid, but also can be used to analyze its purity and structural changes. For example, in the production process of acetic acid, impurities or structurally abnormal products can be quickly detected by infrared spectroscopy.

Infrared spectroscopy can also be used to study the interaction of acetic acid with other substances. For example, by analyzing the infrared spectra of acetic acid mixed with other compounds, the interaction between different functional groups can be understood, thus revealing their interaction mechanism at the molecular level.

Summary

The infrared spectrum of acetic acid has several prominent characteristic peaks, which correspond to the hydroxyl (-OH), carbonyl (C = O) and methoxy (C-O) functional groups in its molecule. By analyzing the wave number position, peak shape and intensity of these characteristic peaks, the molecular structure of acetic acid can be effectively determined and its interaction with other substances can be studied. As an efficient and rapid analysis tool, infrared spectroscopy has important application value in the fields of chemical industry, medicine and material science.