ABSTRACT
Polar groups next to the amine tend to displace the Œrst overtone. An amine next to phosphorus has its Œrst overtone at 6720 (1488 nm) and 7652 cm-1 (1481 nm).1
In the mid-IR region, the amine NH stretch absorption is weak relative to primary alcohols, about 1-2 L/mole-cm compared to 50-100 L/mole-cm.3 However, the intensity of the Œrst overtone of aliphatic amines is of the same order of magnitude as the fundamental. For example, n-butyl amine’s Œrst overtone has an absorptivity of 0.6 L/mole-cm compared to 2.4 L/mole-cm for the fundamental. The overtones of amines and hydroxyls are of about the same magnitude, and it may be easier to detect an amine in the presence of alcohols in the NIR than the mid-IR.
