An infrared IR spectrum helps in determining the molecular structure of a compound by providing information about the presence of specific functional groups within the molecule. Infrared spectroscopy works by measuring the absorption of infrared radiation by the compound, which causes the bonds within the molecule to vibrate at characteristic frequencies. These frequencies are unique to the type of bond and the atoms involved, allowing chemists to identify the functional groups present in the molecule.For example, let's consider the compound ethyl acetate CH3COOCH2CH3 . Ethyl acetate contains several functional groups, including a carbonyl group C=O and an ester linkage C-O-C . In an infrared spectrum, these functional groups will exhibit characteristic absorption bands that can be used to analyze their presence.1. Carbonyl group C=O : The carbonyl group in ethyl acetate will show a strong and sharp absorption band in the range of 1650-1750 cm-1 due to the stretching vibration of the C=O bond. This is a characteristic feature of carbonyl-containing compounds.2. Ester linkage C-O-C : The ester linkage in ethyl acetate will show two absorption bands. The first one is due to the stretching vibration of the C-O bond, which typically appears in the range of 1000-1300 cm-1. The second one is due to the stretching vibration of the C-O-C bond, which appears in the range of 1050-1250 cm-1. These bands are characteristic features of ester-containing compounds.By analyzing the infrared spectrum of ethyl acetate and identifying these characteristic absorption bands, a chemist can confirm the presence of the carbonyl group and the ester linkage in the molecule. This information, combined with other analytical techniques, can help determine the molecular structure of the compound.