Textbook Question
How many signals are produced by each of the following compounds in its
a. 1H NMR spectrum?
4.
5.
6.
15. Analytical Techniques:IR, NMR, Mass Spect
1H NMR:Number of Signals
3:40 minutesProblem 4m,n,o
Textbook Question
How many signals would you expect to see in the 1H NMR spectrum of each of the following compounds?
m. 
n. 
o. 
Verified step by step guidance1
Step 1: Analyze the structure of the compound. The compound consists of a benzene ring and a carbon atom attached to three nitro groups (-NO2). The benzene ring is symmetric, and the substituent (C(NO2)3) is attached to one of its carbons.
Step 2: Determine the symmetry of the molecule. The benzene ring is symmetric, and the substituent does not disrupt this symmetry. This means that equivalent hydrogens on the benzene ring will give the same signal in the 1H NMR spectrum.
Step 3: Identify the unique hydrogen environments. In the benzene ring, there are two sets of equivalent hydrogens due to the symmetry: (a) two hydrogens ortho to the substituent, and (b) two hydrogens meta to the substituent. The para hydrogen is unique and forms a third environment.
Step 4: Count the number of signals. Since there are three unique hydrogen environments in the benzene ring, the 1H NMR spectrum will show three distinct signals.
Step 5: Consider splitting patterns and chemical shifts. The splitting patterns will depend on the coupling between hydrogens in adjacent environments, and the chemical shifts will be influenced by the electron-withdrawing effect of the nitro groups. However, the number of signals remains three.
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Video duration:
3mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nuclear Magnetic Resonance (NMR) Spectroscopy
NMR spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It relies on the magnetic properties of certain nuclei, primarily hydrogen (1H), to provide information about the number of distinct hydrogen environments in a molecule. Each unique hydrogen environment produces a separate signal in the NMR spectrum, allowing chemists to infer structural details.
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Chemical Shifts
Chemical shifts in NMR spectroscopy refer to the variation in resonance frequency of nuclei due to their electronic environment. Different functional groups and molecular structures influence the electron density around hydrogen atoms, leading to shifts in their resonance signals. Understanding chemical shifts helps in predicting the number of signals and their positions in the spectrum, which is crucial for interpreting NMR data.
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Symmetry and Equivalent Protons
In organic molecules, symmetry can lead to equivalent protons, which are protons that experience the same electronic environment and thus produce a single NMR signal. Analyzing the symmetry of a compound helps in determining how many unique signals will appear in the NMR spectrum. For the nitro-substituted benzene compound shown, recognizing the symmetry and the effects of substituents is essential for predicting the number of signals.
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