Intramolecular hydrogen bonds in ethylenediamines and otheraliphatic diamines

Abstract

The fundamental NH stretching bands of 22 aliphatic diamines have been investigated in dilute C2Cl4 solution.N,N′-Dimethyl-1,3-propanediamine and N,N′-dimethyl- and N,N,N′-trimethyl-ethylenediamine exist predominantly in an intramolecularly hydrogen bonded conformation. Such bonding also exists in N-methyl- and N,N -dimethyl-ethylenediamine, in N-methyl- and N,N-dimethyl-1,3-propanediamine, and in amines of the type H2N(CH2-CH2NH)xCH2CH2NH2. For all of the diamines investigated, intramolecular NH···N bonding disappears sharply when the intervening methylene chain length exceeds three units. Integrated band intensity measurements for primary aliphatic diamines H2N(CH2)nNH2 over the range n = 2–12 suggest that intramolecular hydrogen bonds may also play an important role in the conformation of ethylenediamine and 1,3-diaminopropane.