Textbook Question
How can IR spectroscopy be used to distinguish between the following compounds?
e. cyclohexene and cyclohexane
f. a primary amine and a tertiary amine
15. Analytical Techniques:IR, NMR, Mass Spect
Infrared Spectroscopy Table
Problem 48c
Textbook Question
Identify the important bands you would expect to find in an IR spectrum for the following molecules.
(c) 
Verified step by step guidance1
Identify the functional groups present in the molecule. Each functional group has characteristic absorption bands in an IR spectrum.
For each functional group, determine the typical wavenumber range where its absorption band appears. For example, O-H stretches are typically found around 3200-3600 cm-1, C=O stretches around 1700 cm-1, and C-H stretches around 2800-3000 cm-1.
Consider the molecular structure to identify any specific interactions or conjugations that might shift the absorption bands. Conjugation can lower the frequency of C=O stretches, for instance.
Look for any unique or distinguishing features in the molecule that might lead to additional bands or shifts, such as hydrogen bonding, which can broaden and shift O-H stretches.
Compile a list of expected IR bands based on the identified functional groups and any structural considerations, noting the approximate wavenumber ranges for each.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Infrared (IR) Spectroscopy
Infrared spectroscopy is an analytical technique used to identify functional groups in molecules by measuring the absorption of infrared light at different wavelengths. Each functional group absorbs IR radiation at characteristic frequencies, producing a spectrum with peaks that correspond to specific bond vibrations. Understanding these absorption patterns is crucial for interpreting IR spectra.
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General Features of IR Spect
Functional Groups
Functional groups are specific groups of atoms within molecules that have characteristic properties and reactivity. In IR spectroscopy, different functional groups absorb infrared light at distinct frequencies, allowing for their identification. For example, carbonyl groups (C=O) typically show strong absorption around 1700 cm⁻¹, while hydroxyl groups (O-H) exhibit broad peaks around 3200-3600 cm⁻¹.
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Characteristic IR Absorption Bands
Characteristic IR absorption bands are specific regions in an IR spectrum where particular functional groups absorb infrared light. These bands are used to identify the presence of functional groups in a molecule. For instance, alkanes show C-H stretching vibrations around 2850-2960 cm⁻¹, while alkenes have C=C stretching near 1640-1680 cm⁻¹. Recognizing these bands is essential for analyzing and interpreting IR spectra.
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