Column: IR Spectral Interpretation Workshop

, is the founder and CEO of Big Sur Scientific, a maker of portable mid-infrared cannabis analyzers. He has over 30 years experience as an industrial infrared spectroscopist, has published numerous peer-reviewed papers, and has written three books on spectroscopy. As a trainer, he has helped thousands of people around the world improve their infrared analyses. In addition to writing for Spectroscopy, Dr. Smith writes a regular column for its sister publication Cannabis Science and Technology and sits on its editorial board. He earned his PhD in physical chemistry from Dartmouth College.

Articles

One of the biggest practical limitations of infrared spectroscopy is its difficulty in analyzing mixtures. Infrared library searching can help, but it must be done right.

Library Searching

Integrating peak position, height, and width information is important to properly interpret infrared spectra. But do you understand why peak heights and widths vary? We explain.

The Grand Review II: Why Do Different Functional Groups Have Different Peak Heights and Widths?

Articles in this column have addressed five main areas: theory, functional groups containing the C-H bond, those containing the C-O bond, those with the C=O bond, and those with organic nitrogen compounds. Here, we review the concepts.

The Grand Review I: Why Do Different Functional Groups Have Different Peak Positions?

We review one final organic nitrogen functional group, representing explosive compounds. This is the nitro group, which requires a different set of interpretation rules.

Organic Nitrogen Compounds X: Nitro Groups, An Explosive Proposition

Here we delve into the interpretation of another organic nitrogen compound, known as polyurethane, a ubiquitous polymer used for wood finishes and foam rubber.

Organic Nitrogen Compounds IX: Urethanes and Diisocyanates

Here, we continue our examination of the infrared (IR) spectra of organic nitrogen compounds with imides, which are a common chemical intermediate. IR can be used not only to identify imides, but also to distinguish between straight chain and cyclic imides. We explain how.

Organic Nitrogen Compounds VIII: Imides

The N-H stretching and bending peaks can be used to distinguish primary, secondary, and tertiary amides and to ascertain protein structure. Here’s how.

Organic Nitrogen Compounds, VII: Amides—The Rest of the Story

Amides are an important functional group found extensively in polymers and proteins. There are three different families of amides. Here, is explained how to distinguish them using infrared spectroscopy.

Organic Nitrogen Compounds VI: Introduction to Amides

The amine salt functional group contains ionic bonding, and is extremely polar, giving rise to a number of intense and uniquely placed peaks that are easy to identify for primary, secondary, and ter tiary amines.

Organic Nitrogen Compounds V: Amine Salts

Nitriles are easy to spot because of the unusual intensity and position of the C≡N stretching peak.