Methoxy compounds, including methyl carboxylic esters, exhibit a weak band in the 2860–2800 cm−1 region of the infrared spectrum, which is diagnostic for the methoxyl group. The band occurs at a lower frequency than that of the main C—H absorption. The potassium bromide disk technique is satisfactory for solid methoxy compounds. Aldehydes, amino acid hydrochlorides, nitrogen heterocyclic molecules and N-methyl amines exhibit absorption bands which may overlap this region and the detection of a methoxy substituent for these classes of compound may be less precise.
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