Column: IR Spectral Interpretation Workshop

The C=O Bond, Part II: Aldehydes

Nov 01, 2017

By Brian C. Smith

Aldehydes feature a unique “lone hydrogen” atom, giving rise to unique C-H stretching and bending peaks, making them easy to spot. In this installment, a new feature is also presented, “IR Spectral Interpretation Review,” where key concepts from past columns are presented for those new to the column and for readers who need a refresher.

The Carbonyl Group, Part I: Introduction

Sep 01, 2017

By Brian C. Smith

An introduction to the IR spectroscopy of the carbonyl group, exploring why the peak is intense and showing how to apply that knowledge to the analysis of the spectra of ketones

An IR Spectral Interpretation Potpourri: Carbohydrates and Alkynes

Jul 01, 2017

By Brian C. Smith

Two unrelated discussions are presented: carbohydrates and alkynes.

The C-O Bond III: Ethers By a Knockout

May 01, 2017

By Brian C. Smith

We will discuss three different types of ether, which are characterized by the type of carbons attached to the central oxygen.

Alcohols—The Rest of the Story

Apr 01, 2017

By Brian C. Smith

Our survey of the spectroscopy of the C–O bond continues. Here, we complete our discussion of alcohols and discuss how to distinguish pure alcohols, alcohol–water mixtures, and pure water from each other.

IR Spectral Interpretation Workshop Quizzes


Quiz 13: Your latest interpretation problem is seen in the figure presented here. Using what you have learned from the September installment of IR Spectral Interpretation Workshop and previous columns, do your best to assign the peaks in this spectrum, determine the functional groups present, and determine the chemical structure of the molecule that gave rise to this spectrum. Take the quiz!

Quiz 12: Your latest interpretation problem is seen in the figure presented here. Using what you have learned from the July installment of IR Spectral Interpretation Workshop and previous columns, do your best to assign the peaks in this spectrum, determine the functional groups present, and determine the chemical structure of the molecule that gave rise to this spectrum. Ignore the peaks with an x through them. Take the quiz!

Quiz 11: Your latest interpretation problem is seen in the figure below. Using the information provided here and what you have learned from previous columns, do your best to assign the peaks in the spectrum shown in the figure and table, determine the functional groups present, and determine the chemical structure of the molecule that gave rise to this spectrum. Take the quiz!

Quiz 10: Your latest interpretation problem is seen in the figure below. Using the information provided here and what you have learned from previous columns, try to determine the complete chemical structure of this pure compound. At minimum try to determine whether this is an alcohol, and if it is, what type it is. Here's a hint: To make life easier, assume the peak at 2872 is at 2855. Take the quiz!

Quiz 9: The infrared spectrum for your next interpretation exercise is shown in the figure below. Using the information provided here and what you have learned from previous columns, try to determine the complete chemical structure of this pure compound. At minimum try to determine whether this is an alcohol, and if it is, what type it is. Here's a hint: Assume the 2965 and 2938 peaks are the same size. They might not appear so due to a plotting error. Take the quiz!

Quiz 8: Your latest interpretation problem is shown in the figure below. In this problem use what you learned from this column to determine what type of alkene is present, and if possible determine its substituents. The figure below shows the IR spectrum of a liquid measured as a capillary thin film. Take the quiz!

Quiz 7: First, determine why Table I fails for this spectrum, then using only the benzene fingers; determine the substitution pattern around the benzene ring present in the molecular structure. If possible, use the rest of the spectrum to determine the complete molecular structure of the molecule.  Take the quiz!

Quiz 6: This quiz is a two-parter. Using what you learned so far, give the substitution pattern and attempt to name each of the “molecules” seen in Figure 1. In the bottom of the figure there is a “chemical reaction”—try to name it if you can. The second and more serious part of this quiz is to finalize the identification of the molecule in the last problem (shown in Figure 2). Take the quiz!

Quiz 5: Do your best to assign all the peaks shown in the figure and table to determine the functional groups present. There is one aspect of this molecule's structure you will not be able to determine because we have not yet talked about it. Take the quiz!

Quiz 4: Do your best to assign all the peaks shown in the figure and table to determine the functional groups present. Then, put the functional groups together to come up with a proposed chemical structure. Take the quiz!

Quiz 3: Using the peak positions shown in the figure and table, do your best to assign all the peaks to determine the functional groups present. Then, put the functional groups together to come up with a proposed chemical structure. Feel free to make use of reference spectra already published in these columns. Take the quiz!

Quiz 2: Using the peak positions shown in the figure, do your best to assign all the peaks to determine the functional groups present. Then, put the functional groups together to come up with a proposed chemical structure. Take the quiz!

Quiz 1: Examine the spectrum in the figure, determine from the pattern of peaks whether the sample contains methyl groups, methylene groups, or both, and then assign as many of the peaks as you can. Take the quiz!

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