Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy

Problem 30e,f

Chapter 14, Problem 30e,f

For each of the following pairs of compounds, name one absorption band that can be used to distinguish between them.
e.
f.

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Identify the functional groups present in each compound in the pair. Functional groups often have characteristic absorption bands in an IR spectrum.

Consult an IR spectroscopy table to determine the wavenumber ranges for the characteristic absorption bands of the functional groups identified in each compound.

Compare the functional groups in the two compounds. Look for a functional group that is present in one compound but absent in the other. This will help you identify a distinguishing absorption band.

For the compound with the unique functional group, note the specific wavenumber range where its characteristic absorption band appears. For example, a carbonyl group (C=O) typically absorbs around 1700 cm⁻¹, while an alcohol (O-H) shows a broad band around 3200-3600 cm⁻¹.

State the absorption band (wavenumber range) that can be used to distinguish between the two compounds based on the presence or absence of the functional group.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Infrared Spectroscopy

Infrared spectroscopy is a technique used to identify functional groups in organic compounds by measuring the absorption of infrared light. Different bonds absorb characteristic frequencies of IR radiation, leading to distinct absorption bands in the spectrum. Understanding how to interpret these bands is crucial for distinguishing between compounds based on their functional groups.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Common functional groups include hydroxyl (-OH), carbonyl (C=O), and carboxyl (-COOH). Identifying these groups helps in predicting the behavior of compounds and is essential for recognizing differences between similar molecules.

Absorption Bands

Absorption bands in an IR spectrum correspond to the specific wavelengths at which a compound absorbs infrared light due to vibrational transitions of its molecular bonds. Each type of bond and functional group has a unique absorption band, allowing chemists to differentiate between compounds. Recognizing these bands is key to analyzing and interpreting IR spectra effectively.

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Major IR absorptions

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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

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Textbook Question

A 4.0 × 10^-5 M solution of a compound in hexane shows an absorbance of 0.40 at 252 nm in a cell with a 1 cm light path. What is the molar absorptivity of the compound in hexane at 252 nm?

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Textbook Question

For each of the following pairs of compounds, name one absorption band that can be used to distinguish between them.

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Textbook Question

Identify the compound that gives the mass spectrum and infrared spectrum shown here.

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Textbook Question