Textbook Question
An unknown compound (C₇H₆O) gives the IR spectrum shown here. At what chemical shifts would you expect to see signals in the ¹H NMR spectrum?
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15. Analytical Techniques: IR, NMR, Mass Spect
1H NMR - Chemical Shifts
Multiple Choice
Which of the labeled protons absorbs energy most upfield in the 1H NMR?
A
A
B
B
C
C
D
D
E
E
Verified step by step guidance1
Identify the different types of protons in the molecule. Consider factors such as the chemical environment, including electronegative atoms, pi bonds, and hybridization of the carbon atoms to which the protons are attached.
Understand the concept of chemical shift in 1H NMR spectroscopy. Protons in different environments absorb energy at different frequencies, which is reflected in their chemical shift values. Upfield shifts correspond to lower frequency (lower ppm) and are typically associated with protons in less deshielded environments.
Analyze the electronic environment of each labeled proton. Protons that are more shielded by electron density will absorb energy more upfield. Consider the presence of electron-donating groups or the absence of electron-withdrawing groups.
Compare the chemical environments of the labeled protons. Protons attached to carbons that are not adjacent to electronegative atoms or pi systems are generally more shielded and thus absorb upfield.
Determine which labeled proton is in the most shielded environment based on your analysis. This proton will absorb energy most upfield in the 1H NMR spectrum.
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