The qualitative aspects of infrared spectroscopy are one of the most powerful attributes of this diverse and versatile analytical technique. Over the years, much has been published in terms of the fundamental absorption frequencies which are the key to unlocking the structure–spectral relationships of associated molecular vibrations. Applying this knowledge at the practical routine level tends to be a mixture of art and science. While many purists will argue against this statement, this author believes that it is not possible to teach a person to become proficient as an interpretive spectroscopist by merely presenting the known relationships between structure and the observed spectra. Instead, the practical approach, which has been adopted in this text, is to help the reader appreciate the visual aspects of the spectroscopy and how to interpret these relative to the structure and chemistry of the sample. This is achieved by recognizing characteristic shape and pattern within the spectrum, and by applying the information obtained from published group frequency data, along with other chemical and physical data from the sample. Included in the text is a discussion of the interrelationships that exist between the practical side of acquiring the spectrum, the chemistry and physics of the sample under study, the physical interactions of the sample with its environment, and the impact of the structure on the spectrum. In essence, the interpretation of infrared spectra is much more than simply assigning group frequencies. The spectrum is rich in information, and this article is intended to help the reader to extract the maximum using the knowledge available for the sample and the acquired spectral data. One important factor to bear in mind is that a successful interpretation is based not only on the presence of particular bands within the spectrum, but also the absence of other important bands.
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