Strong Absorption of IR Radiation: Water has strong absorption bands in the mid-infrared region, particularly around 3500-3200 cm-1 due to O-H stretching vibrations. These intense absorption bands can interfere with and obscure the absorption bands of the sample being analyzed.
Interfering Hydrogen Bonds: Water molecules can form intermolecular hydrogen bonds with the sample molecules, altering their chemical structure and vibrational frequencies. This can lead to changes or distortions in the IR spectrum of the sample, making it difficult to interpret the characteristic peaks.
Low Solubility of Many Organic Compounds: Water is a polar solvent, and it is not suitable for dissolving many organic compounds, which are typically nonpolar or only slightly polar. This limits the range of samples that can be analyzed using water as a solvent in IR spectroscopy.
Variable Composition: The composition of water can vary depending on factors such as temperature, humidity, and the presence of dissolved gases. This can lead to inconsistent and unreliable IR spectra, making it difficult to obtain reproducible results.
For these reasons, IR spectroscopists typically use other solvents that are transparent in the infrared region, such as carbon tetrachloride (CCl4), chloroform (CHCl3), or dichloromethane (CH2Cl2). These solvents have minimal interference with the IR spectrum of the sample and allow for better analysis of the characteristic absorption bands.
