Hydrogen bonding and related association in linear aliphatic amino alcohols as probed by carbon-13 spin-lattice relaxation times

Abstract

Carbon-13 chemical shifts and spin-lattice relaxation data obtained in a number of solvents for five linear aliphatic amino alcohols are presented. The purpose of monitoring the relaxation behavior was to learn about inter- and intramolecular association as a function of concentration and solvent. An analyses of the T/sub 1/, C13 spin-lattice relaxation time, data reveals that intermolecular OH-OH hydrogen bonding competes efficiently with OH-NH hydrogen bonding in neat solution and in chloroform solution. Moreover, overall diffusion is slower in 2-aminoethanol than for the next few homologues in these media. This observation is in agreement with certain ir studies where intermolecular hydrogen bonding has been shown to be more favorable in cases like 2-aminoethanol. The results presented for water and dimethyl sulfoxide solutions reveal that intermolecular solute-solute interactions decrease; for 6-aminohexanol the T/sub 1/ pattern gives evidence for tumbling via an open-chain structure. Finally, the agreement between calculated T/sub 1/'s, using a basic isotropic diffusion model and experimental data, is briefly discussed.