CONFORMATIONAL CHANGES UPON COMPLEXATION: THE MICROWAVE SPECTRA AND STRUCTURES OF 2-AMINOETHANOL VAN DER WAALS COMPLEXES

$^{a}$R. E. Penn, R. F. Curl, Jr. J. Chem. Phys. 55, 651 (1971)Author Institution: Department of Chemistry, Kent State UniversityRotational spectra of the van der Waals complexes of 2-aminoethanol-water and 2-aminoethanol-argon have been recorded using a Fourier-transform microwave spectrometer. Eleven a- and b-type transitions were fit to the Watson A-reduction Hamiltonian for 2-aminoethanol-water yielding A = 4886.29 (7) MHz, B = 3355.93 (8) MHz, and C = 2311.66 (4) MHz, and twelve a-, b-, and c-type transitions for 2-aminoethanol-argon were fit to $A = 4986.16$ (12) MHz, $B = 1330.190$ (7) MHz, and $C = 1143.831$ (6) MHz. The spectra are identified with ab initio structures of the two complexes. The 2-aminoethanol monomer has an intramolecular hydrogen bond from the hydroxyl group to the $amine;^{a}$ the O - C - C - N torsional angle is $58^{\circ}$ and the O - N distance is $2.83 {\AA}$. The argon complex is based on the 2-aminoethanol monomer conformation, and the argon sits $3.91 {\AA}$ from the nitrogen and $3.49 {\AA}$ from the oxygen. The 2-aminoethanol-water complex is stabilized by hydrogen bonds from the hydroxyl to the water oxygen and from water to the amino nitrogen. Formation of the intermolecular hydrogen bonds requires the O - C - C - N torsional angle to increase to $71^{\circ}$, and the O - N distance increases to $3.04 {\AA}$. Rotational spectra of the ${^{13}}C$ isotopomers of the 2-aminoethanol monomer have been recorded and enable a substitution structure of the heavy atoms to be determined