What functional groups correspond to the characteristic peaks of the infrared spectrum (IR) of styrene?

What functional groups correspond to the characteristic peaks of the infrared spectrum (IR) of styrene?

Infrared spectroscopy (IR) is a commonly used analytical technique that can detect and identify functional groups in substances through changes in molecular vibration and rotational frequency. As an important chemical raw material, styrene contains two typical functional groups in its molecular structure: benzene ring and carbon-carbon double bond (C = C). In this paper, the characteristic peaks of infrared spectrum of styrene and its corresponding functional groups are analyzed in detail.

Molecular Structure and Main Functional Groups of Styrene

styrene (C-HLY-CH = CH₂) is an unsaturated compound containing a benzene ring and a carbon-carbon double bond. In its molecular structure, the presence of benzene ring and double bond makes styrene exhibit unique characteristic peaks in the infrared spectrum. The C = C bond on the benzene ring and the adjacent C- H bonds give rise to specific absorption peaks, and the symmetric and asymmetric stretching vibrations of the carbon-carbon double bond (C = C) also appear in specific wave number ranges.

Main characteristic peaks of infrared spectra of styrene

1. C = C stretching vibration of benzene ring The C = C bond in the benzene ring is a rigid structure, and its symmetrical and asymmetrical stretching vibrations usually occur in the range of 1450-1600 cms¹. Due to the special conjugated structure of the benzene ring, the vibration frequency of the C = C bond will be affected by the adjacent substituents, but in general, the stretching vibration of the C = C bond is an important symbol of the structure of the benzene ring.

2. C- H stretching vibration on benzene ring The C- H bond on the benzene ring is sp² hybridized, and its stretching vibration usually occurs in the range of 3000-3100 cm¹. These peaks usually appear as broad and strong absorption peaks, and due to the symmetry of the benzene ring, a plurality of peaks or a broadened peak may appear. These peaks are direct evidence for the presence of benzene ring functional groups.

3. C = C stretching vibration of carbon-carbon double bond The carbon-carbon double bond (CH = CH₂) in the styrene molecule is a non-conjugated structure, and its symmetric and asymmetric stretching vibrations usually occur in the range of 1600-1680 cms¹. Due to the non-conjugation of the double bond, its vibrational frequency will be slightly lower than that of the C = C bond in the benzene ring. The characteristic peak of this region is an important basis for judging whether there is a double bond in styrene.

Analysis of other characteristic peaks

in addition to the characteristic peaks of the main functional groups mentioned above, other minor peaks may be observed in the infrared spectrum of styrene, such:

• C- C Bending Vibration on Benzene Ring: Usually appear in the range of 800-900 cm¹. These peaks reflect the bending vibration of the benzene ring and are indirect evidence of the existence of the benzene ring.
• C- H flexural vibrations near a double bond: In the range of 600-700 cm¹, these peaks are usually related to the C- H bond bending vibration near the double bond.

Factors Affecting the Infrared Spectral Peak

in the actual infrared spectrum analysis, the characteristic peak of styrene may be affected by many factors, such as the purity of the sample, the dispersion state, and the test conditions (such as the compression method or the solution method). Especially for the characteristic peaks of double bonds and benzene rings, slight shifts may occur due to intermolecular interactions or changes in the external environment. Therefore, in the analysis of the infrared spectrum of styrene, it is necessary to combine the specific experimental conditions and spectral characteristics to make a comprehensive judgment.

Application of Infrared Spectroscopy of Styrene

the infrared spectrum analysis of styrene has important application value in chemical industry. For example, in quality control, the purity and structural integrity of styrene can be judged by analyzing its infrared spectrum; in research, infrared spectroscopy can provide important information for the chemical reaction mechanism and structural characteristics of styrene.

Summary

the characteristic peaks of the infrared spectrum of styrene are mainly determined by the benzene ring and carbon-carbon double bond in its molecular structure. By analyzing the characteristic peaks in the ranges of 1450-1600 cm¹, 3000-3100 cm¹ and 1600-1680 cm¹, the functional groups in styrene can be accurately identified. These characteristic peaks not only reflect the molecular structure of styrene, but also provide an important analytical means for its application in chemical production and research.