Book cover for Organic Chemistry

Organic Chemistry

John McMurry

ISBN #9781305080485

9th Edition

1,986 Questions

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Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
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Summary

NMR spectroscopy is a powerful tool for molecular structure determination based on the behavior of nuclear spins in an external magnetic field. By analyzing chemical shifts, integration, and spin-spin splitting patterns in 1H NMR spectra, chemists can deduce the electronic environment and connectivity of protons. The 13C NMR technique, enhanced by FT–NMR and DEPT experiments, offers complementary information about the carbon framework of molecules. Together, these methods not only solve complex structural puzzles in organic chemistry but also translate into practical applications in drug design and medical imaging (MRI).

Learning Objectives

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Key Concepts

CONCEPT

DEFINITION

Acid–Base Chemistry

The study of acids and bases using both the Brønsted–Lowry (proton-donating/accepting) and Lewis (electron pair accepting/donating) frameworks, including quantification via pKa values, which together explain chemical reactivity in organic molecules. •

Example Problems

Example 1

The amount of energy required to spin-flip a nucleus depends both on the strength of the external magnetic field and on the nucleus. At a field strength of $4.7 \mathrm{~T}, \mathrm{rf}$ energy of $200 \mathrm{MHz}$ is required to bring a ${ }^{1} \mathrm{H}$ nucleus into resonance, but energy of only $187 \mathrm{MHz}$ will bring a ${ }^{19} \mathrm{~F}$ nucleus into resonance. Calculate the amount of energy required to spin-flip a ${ }^{19} \mathrm{~F}$ nucleus. Is this amount greater or less than that required to spin-flip a ${ }^{1} \mathrm{H}$ nucleus?

Example 2

Calculate the amount of energy required to spin-flip a proton in a spectrometer operating at $300 \mathrm{MHz}$. Does increasing the spectrometer frequency from 200 to $300 \mathrm{MHz}$ increase or decrease the amount of energy necessary for resonance?

Example 3

2-Chloropropene shows signals for three kinds of protons in its ${ }^{1} \mathrm{H}$ NMR spectrum. Explain.

Example 4

The following ${ }^{1} \mathrm{H}$ NMR peaks were recorded on a spectrometer operating at $200 \mathrm{MHz}$. Convert each into $\delta$ units. (a) CHCl $_{3} ; 1454 \mathrm{~Hz}$. (b) $\mathrm{CH}_{3} \mathrm{Cl} ; 610 \mathrm{~Hz}$ (c) $\mathrm{CH}_{3} \mathrm{OH} ; 693 \mathrm{~Hz}$ (d) $\mathrm{CH}_{2} \mathrm{Cl}_{2} ; 1060 \mathrm{~Hz}$

Example 5

When the ${ }^{1} \mathrm{H}$ NMR spectrum of acetone, $\mathrm{CH}_{3} \mathrm{COCH}_{3}$, is recorded on an instrument operating at $200 \mathrm{MHz}$, a single sharp resonance at $2.1 \delta$ is seen. (a) How many hertz downfield from TMS does the acetone resonance correspond to? (b) If the ${ }^{1} \mathrm{H}$ NMR spectrum of acetone were recorded at $500 \mathrm{MHz}$, what would the position of the absorption be in $\delta$ units? (c) How many hertz downfield from TMS does this $500 \mathrm{MHz}$ resonance correspond to?
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