Identify which one of the three methods of analysis (i. e., TLC, IR and melting point) provides information about the structure of an unknown compound. Explain why structural information cannot be obtained using the other two met

IR provides structural information about a molecule. TLC and melting point analysis do not provide structural information.

Explanation:

IR gives information about the functional groups present in a molecule. The vibrational frequency of each functional group gives information about the structure of the entire molecule.

Structural features of a molecule are deduced by matching the vibrational frequencies of  groups obtained from the IR spectroscopy with that of known functional groups in literature.

Melting point is a qualitative method that can only yield information about the identity of a compound and not its structure. Each compound has its unique melting point recorded in literature and any pure sample of the same compound must have the same sharp meting point.

Thin-layer chromatography (TLC) is a chromatography technique used to separate non-volatile mixtures. After separating the components of the mixture, it does not give any information regarding the identity or the structure  of the components of the mixture.

Therefore, only IR yields structural information about a sample.