The aim of this report is to demonstrate that the combination bands of NH2are useful to compare the association interactions of the NH2group of primary aliphatic amines with the recognized weak proton donor solvents, chloroform and isopropyl alcohol for example and with the weaker π-electron donors benzene and pyridine, for example. Examples of families of isosbestic curves characteristic of typical equilibrium reactions of an amine with the complexing solvents are presented including the proton donor-acceptor system, 4-phenylbutylamine with benzene.