Blog post: Genecks: How to read an IR spectrum

Author: Genecks

One of the things I have been meaning to write about is how I have gone about reading an IR spectrum. I think that many people hold confusion when it comes about reading IR spectra. However, it can be broken down into simple methods and steps. I will not go into detail, but I will provide some basics of how I go about reading an IR spectra. As I have not done it in a long time, I will give some advice that I think any person reading an IR spectra can use in order to help keep the methodology understood.

One of the first things to keep in mind is that certain bonds occur about certain wavelengths. As such, a person has to keep a memory of what bonds occur at what wavelengths. Nonetheless, it can still be problematic to scan about an IR spectra in attempting to assign bonds and develop an understanding of what kind of molecule an individual is looking at.

As such, I think the way I entertain reading an IR spectra is to use a left to right methodology. I think, for the most part, an IR spectra goes from general to specific as you move from left to right while reading an IR spectra. So, if you're looking at the left-most part of an IR spectra, there are not as many bonds to interpret to exist as there would be as you move more to the right while viewing the peaks and curves of an IR spectra. As you move more toward the right of the IR spectra, you start to realize that there are more specific kinds of bonds that can occur.

So, it can be boiled down to a few basic principles:

1) Left to right processing of visual information to determine the bonds

2) Memorization of the bonds that occur from left to right that may exist within particular wavelength regions while reading an IR spectra from left to right

Once a person can generalize and understand what kind of bonds an individual is coming across while interpreting the peaks on an IR spectrum, and individual can attempt to analyze the fingerprint region on an IR spectrum. For a person who becomes more proficient at interpreting a fingerprint region on an IR spectrum, there becomes a level of ease during which an individual can more easily interpret the IR spectrum. In my experience, the fingerprint region can be intimidating, but it can offer clues as to what kind of molecule a person is looking at.

So, in a way, moving from left to right while analyzing the IR spectrum means analyzing from general to specific.
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