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What do the 3:2:1 peak intensities in the proton NMR spectrum of ethyl alcohol represent?
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magnetic resonance
Figure 1: Precession of a magnetic dipole moment μ in the presence of a constant field H and a rotating field H′ (see text)
In the proton NMR spectrum of ethyl alcohol (CH₃–CH₂–OH), the 3:2:1 peak intensities represent the relative number of hydrogen atoms contributing to each signal.1
In proton magnetic resonance spectroscopy, the area under each absorption peak is directly proportional to the number of hydrogen atoms in a specific bonding environment. For ethyl alcohol, the three distinct peaks correspond to the following groups:23
- 3: The three equivalent hydrogen atoms of the CH₃ group.1
- 2: The two equivalent hydrogen atoms of the CH₂ group.1
- 1: The single hydrogen atom of the OH group.1
By using a process called integration, spectrometers calculate the area under these peaks, allowing chemists to determine the ratio of hydrogen atoms present in different parts of the molecule, which is essential for assigning molecular structures.23