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How does the proton NMR spectrum of methanol reveal two hydrogen environments?

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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 proton nuclear magnetic resonance (NMR) spectroscopy, the spectrum of methanol (CH₃OH) reveals two distinct hydrogen environments because the molecule contains two different types of bonding arrangements for its hydrogen atoms.1

In the methanol molecule, three hydrogen atoms are bonded to a carbon atom, while one hydrogen atom is bonded to an oxygen atom. Because these hydrogen atoms exist in different chemical environments, they experience different local magnetic fields due to the influence of nearby electrons and the electronegativity of the atoms to which they are attached.12

This difference in local magnetic fields results in the hydrogen atoms absorbing radiation at different frequencies. In an NMR spectrum, this is observed as two separate peaks at different positions, a phenomenon known as chemical shift. These shifts allow chemists to identify the distinct structural environments of the hydrogen atoms within the molecule.12