Final answer:
IR spectroscopy provides key information on the molecular structure of a compound, helping to identify functional groups and indicating specific chemical reactions.
Step-by-step explanation:
The key information gained from IR spectroscopy is molecular structure. By observing which wavelengths a molecule absorbs, and to what extent it absorbs them, we can gain information about the nature of the energetic transitions that a molecule is able to undergo, and thus information about its molecular structure. IR spectroscopy provides insights into the presence or absence of key functional groups within a molecule, which may indicate the occurrence of specific chemical reactions, such as the conversion of a ketone group to an alcohol. Though IR spectroscopy alone may not reveal the complete structure of a molecule, it is a valuable tool in conjunction with other analytical methods.