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Ch. 15 - Structural Identification 2: Nuclear Magnetic Resonance Spectroscopy
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
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Tutti i libri di testoMullins 1st EditionCh. 15 - Structural Identification 2: Nuclear Magnetic Resonance SpectroscopyProblema 76
Capitolo 14, Problema 76

For the compound shown, produce a table of the shift, integration, and multiplicity of each peak you would expect to see in a ¹H NMR spectrum.
Chemical structure of 4-methylpent-3-en-2-one, showing a benzene ring, ketone group, and alkene side chain.

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1
Identify the different types of hydrogen environments in the compound. Look for unique groups or atoms that might affect the chemical shift, such as electronegative atoms or pi bonds.
Estimate the chemical shift for each type of hydrogen. Use typical chemical shift ranges for common functional groups and environments. For example, alkane hydrogens typically appear between 0-2 ppm, while hydrogens on a carbon adjacent to an electronegative atom might appear between 3-4 ppm.
Determine the integration for each peak. This corresponds to the number of hydrogens in each environment. Count the hydrogens in each distinct environment to determine the relative area under each peak.
Analyze the multiplicity of each peak. Consider the number of neighboring hydrogens (n) and apply the n+1 rule to determine the splitting pattern. For example, a hydrogen with two neighboring hydrogens will appear as a triplet.
Create a table summarizing the chemical shift, integration, and multiplicity for each type of hydrogen in the compound. Ensure that each entry in the table corresponds to a distinct hydrogen environment identified in the first step.

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Chemical Shift in ¹H NMR

Chemical shift refers to the position of an NMR signal relative to a standard reference, typically tetramethylsilane (TMS). It indicates the electronic environment of hydrogen atoms in a molecule, affected by nearby electronegative atoms or functional groups. Understanding chemical shifts helps predict where peaks will appear in the spectrum.
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1H NMR Chemical Shifts

Integration in ¹H NMR

Integration in ¹H NMR quantifies the area under each peak, corresponding to the number of hydrogen atoms contributing to that signal. It provides insight into the relative number of protons in different environments within the molecule, aiding in determining the molecular structure.
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1H NMR Integration

Multiplicity in ¹H NMR

Multiplicity describes the splitting pattern of NMR signals, resulting from spin-spin coupling between neighboring hydrogen atoms. The number of peaks in a multiplet follows the n+1 rule, where n is the number of adjacent protons. Multiplicity reveals information about the connectivity and proximity of hydrogen atoms in the molecule.
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1H NMR Chemical Shifts
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Given the ¹H NMR spectrum and the molecular formula, suggest a structure for each molecule. [The IR spectrum suggests the presence of two C=O bonds.]

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Draw the 13C NMR spectrum you would expect to see for each of the molecules shown.

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