Microwave Spectrum of 2-Aminoethanol: Structural Effects of the Hydrogen Bond

Abstract

The microwave spectra of six singly substituted isotropic species of 2-aminoethanol have been observed and assigned. The molecule has been found to exist in a gauche form with an intramolecular hydrogen bond of the O–H···N type. The rs structure of the groups involved in the hydrogen bond obtained is striking primarily in having an unusually long OH bond distance of 1.14 Å. The internal rotation dihedral angles assume values which minimize the distance between the hydroxyl proton and the lone-pair electrons of the nitrogen. This corresponds to the OH bond halfway between the eclipsed and staggered conformation with respect to the C–C bond. The dipole moment was determined from Stark effect measurements to be 3.05 ± 0.05 D and agrees well in magnitude and direction with that predicted by adding the moments of the alcohol and amine groups. The nitrogen nuclear quadrupole coupling constants were determined and agree well with those expected for an amine group not involved in hydrogen bonding.