Textbook Question
How many signals are produced by each of the following compounds in its
b. 13C NMR spectrum?
5.
15. Analytical Techniques:IR, NMR, Mass Spect
Carbon NMR
3:53 minutesProblem 47b(1)
Textbook Question
How many signals are produced by each of the following compounds in its
b. 13C NMR spectrum?
1. 
Verified step by step guidance1
Step 1: Analyze the structure of the compound. The molecule consists of a benzene ring substituted with an isopropyl group and an ethoxy group. Each carbon atom in the molecule needs to be evaluated for symmetry and chemical environment.
Step 2: Determine the symmetry of the benzene ring. The benzene ring has two substituents in a para arrangement (opposite sides). This symmetry means that the carbons in the benzene ring will produce fewer unique signals due to equivalent environments.
Step 3: Evaluate the isopropyl group. The isopropyl group has two methyl carbons that are equivalent due to symmetry, and one carbon attached to the benzene ring. These will contribute distinct signals.
Step 4: Evaluate the ethoxy group. The ethoxy group has two distinct carbons: one directly attached to the benzene ring (oxygen-bound carbon) and one in the ethyl chain. These carbons are in different environments and will produce unique signals.
Step 5: Count the total number of unique carbon environments. Combine the contributions from the benzene ring, isopropyl group, and ethoxy group to determine the total number of signals in the 13C NMR spectrum.
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Video duration:
3mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Carbon Environment in NMR
In 13C NMR spectroscopy, each unique carbon environment in a molecule produces a distinct signal. The environment is determined by the carbon's connectivity and the surrounding atoms. For example, carbons bonded to different functional groups or in different hybridization states will resonate at different chemical shifts, leading to multiple signals in the spectrum.
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13C NMR General Features
Symmetry and Signal Count
The symmetry of a molecule significantly affects the number of signals observed in its NMR spectrum. If a molecule has symmetrical elements, some carbon environments may be equivalent, resulting in fewer signals. Analyzing the structure for symmetry can help predict how many unique signals will appear in the 13C NMR spectrum.
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Integration and Signal Intensity
In NMR spectroscopy, the area under each signal (integration) correlates with the number of equivalent nuclei contributing to that signal. While 13C NMR does not provide direct integration like 1H NMR, understanding the relative intensities of signals can help infer the number of equivalent carbons in the molecule, aiding in the interpretation of the spectrum.
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