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Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
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All textbooksMullins 1st EditionCh. 14 - Structural Identification I: Infrared Spectroscopy and Mass SpectrometryProblem 64
Chapter 13, Problem 64

Give the structure of the molecule that gives rise to the following IR and mass spectra.
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Examine the IR spectrum for characteristic peaks. Look for broad peaks around 3300 cm-1 which indicate O-H or N-H bonds, sharp peaks around 1700 cm-1 for C=O bonds, and peaks around 1600 cm-1 for C=C bonds.
Identify the functional groups present in the molecule based on the IR spectrum. For example, a peak around 1700 cm-1 suggests a carbonyl group, while a broad peak around 3300 cm-1 suggests an alcohol or amine.
Analyze the mass spectrum to determine the molecular weight of the compound. The peak with the highest m/z value is typically the molecular ion peak, which gives the molecular weight of the compound.
Look for fragmentation patterns in the mass spectrum that can provide clues about the structure of the molecule. Common fragments can indicate the presence of certain functional groups or structural features.
Combine the information from the IR and mass spectra to propose a structure for the molecule. Consider the molecular weight, functional groups, and any fragmentation patterns to deduce the most likely structure.

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Key Concepts

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

Infrared (IR) Spectroscopy

IR spectroscopy is a technique used to identify molecular structures based on the absorption of infrared light by the sample. Different functional groups absorb characteristic wavelengths, leading to distinct peaks in the IR spectrum. By analyzing these peaks, one can infer the presence of specific bonds, such as O-H, C=O, or N-H, which are crucial for determining the molecular structure.
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Mass Spectrometry

Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of ions. In the mass spectrum, peaks correspond to different ions, with the x-axis representing m/z (mass-to-charge ratio) and the y-axis showing relative intensity. The molecular ion peak can provide the molecular weight of the compound, while fragment peaks help deduce structural information about the molecule.
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Molecular Structure Elucidation

Molecular structure elucidation involves using data from techniques like IR and MS to deduce the chemical structure of a compound. By correlating the functional groups identified in the IR spectrum with the molecular weight and fragmentation patterns from the mass spectrum, one can construct a plausible structure for the molecule in question, integrating information from both analytical methods.
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Related Practice
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For each of the molecules shown, predict the structure of at least one major fragment in the mass spectrum.

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For each of the molecules shown, predict the structure of at least one major fragment in the mass spectrum.

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