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Ch. 14 - NMR Spectroscopy
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
Chapter 15, Problem 65

The 1H NMR spectrum of 2-propen-1-ol is shown here. Indicate the protons in the molecule that are responsible for each of the signals in the spectrum.
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Step 1: Analyze the molecular structure of 2-propen-1-ol (CH2=CH-CH2OH). It contains three types of protons: the vinyl protons (CH2=CH), the methylene protons (CH2OH), and the hydroxyl proton (-OH).
Step 2: Examine the 1H NMR spectrum. The chemical shift values (in ppm) and splitting patterns provide clues about the environment of each proton type. For example, vinyl protons typically appear downfield (higher ppm), while methylene and hydroxyl protons appear upfield (lower ppm).
Step 3: Assign the signal at approximately 4 ppm to the hydroxyl proton (-OH). This proton is deshielded due to its attachment to the electronegative oxygen atom.
Step 4: Assign the signal at approximately 3 ppm to the methylene protons (CH2OH). These protons are slightly deshielded due to their proximity to the hydroxyl group.
Step 5: Assign the signal at approximately 2 ppm to the vinyl protons (CH2=CH). These protons are deshielded due to the electron-withdrawing effect of the double bond.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Proton NMR Spectroscopy

Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy is a technique used to determine the structure of organic compounds by analyzing the magnetic environment of hydrogen atoms in a molecule. Each unique hydrogen environment produces a signal at a specific chemical shift (measured in ppm), allowing chemists to infer the number and type of protons present.
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Chemical Shift

Chemical shift refers to the position of a signal in the NMR spectrum, which indicates the electronic environment surrounding the hydrogen atoms. Protons in different environments (e.g., near electronegative atoms or in aliphatic vs. aromatic regions) resonate at different frequencies, leading to distinct peaks in the spectrum that can be used to identify functional groups and molecular structure.
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Integration and Multiplicity

Integration in NMR refers to the area under a peak, which correlates to the number of protons contributing to that signal. Multiplicity indicates the splitting pattern of the peaks, which arises from neighboring protons (n+1 rule). Understanding these concepts helps in determining how many protons are in each environment and their connectivity within the molecule.
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