Intramolecular hydrogen bonding and intermolecular association of amino alcohols

Abstract

Infrared spectral studies of the hydrogen-bonding behaviour of aminoethanol and aminopropanols have revealed that they form the strongest intramolecular hydrogen bonds among the substituted alcohols X(CH₂)_2,3,4OH where X = F, Cl, Br, I, OH, OCH₃I, NR₂(RH, alkyl) in a given series, establishing the importance of basicity in the hydrogen-bonding interaction. Strong intramolecular hydrogen bonding was found to reduce considerably their association tendency so that there were large amounts of intramolecularly hydrogen-bonded species in concentrated solution. The limited numbers of associated species formed were largely composed of closed dimers, whose nature depended on the strength of intramolecular hydrogen-bond. In dimethylaminoethanol and 3-aminopropanol, the dimers involved the participation of nitrogen so that fairly large ring dimers (ten- and twelve-membered, respectively) were formed. In the case of diethylaminopropanol, since the intramolecular hydrogen bond was very strong, the intermolecular association was limited to small amounts of free hydroxy monomers.