By itself, Infrared (IR) spectroscopy isn’t a great technique for fixing the structure of one unknown molecule. However, we’ve viewed that IR spectroscopy can a great technique for identifying certain functional groups in one unknown molecule – especially functional groups containing five or C=O.

You are watching: Given the structure below, which ir absorption band is inconsistant with the structure?

For instance, in one earlier write-up on the structure determination of deer tarsal gland pheromone, us saw just how the writer of the study provided IR spectroscopy to identify the visibility of a lactone functional team (i.e. A cyclic ester) by its properties absorbance at 1775 cm-1.

Additionally, if you’ve narrowed under a framework to several possibilities, it have the right to be very helpful in ruling various possibilities out.

In this post we’re walking to go through four (simple) practice troubles where you’ll be provided with an IR spectrum and the molecule formula, and are climate charged through the task of figuring the end which molecule best fits the spectrum.

Everything you must know around IR in stimulate to settle the problems below was gift in the previous short article on exactly how to do fast analyses that IR spectra, for this reason go ago and read that if girlfriend haven’t excellent so already.

Let’s begin.

(answers to each problem, along with analysis, room at the bottom that the post. Don’t peek until you’ve given each trouble a thorough attempt).

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Table that Contents

Problem #1: Unknown molecule through molecular formula C5H10O. Which of these 5 molecules is the most likely to be?

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There’s likely room for a 3rd post ~ above IR spectroscopy covering some much more rarely encountered useful groups and also other minutiae. Yet for currently we’re walking to relocate on to the next technique, mass spectrometry (MS) in the next article in this series.