Intramolecular hydrogen bond stabilized conformation of 3-aminopropanol

Abstract

Rotational spectra of the most abundant, three 13C, and the 15N isotopologues of 3-aminopropanol have been recorded in natural abundance using a Fourier-transform microwave spectrometer. For the most abundant isotopologue, 54 hyperfine components from the thirteen a- and b-type transitions measured were fit to the quadupole coupling constants, χaa = −2.551(1) MHz, χbb = 1.248(1) MHz. Rotational and centrifugal distortion constants determined from fits of the resulting unsplit line centers to the Watson A-reduction Hamiltonian are A = 7405.303(1) MHz, B = 3868.1925(5) MHz, C = 2829.2615(7) MHz, ΔJ = 1.90(3) kHz, ΔJK = −0.5(3) kHz, ΔK = 2.7(3) kHz, δJ = 0.5(4) kHz, and δK = 4.0(4) kHz. Five to six transitions were measured for each of the 13C and 15N isotopologues and rotational constants were determined by fixing the distortion constants to the values found for the normal isotope. The five sets of moments of inertia were used to determine the 3-aminopropanol substitution structure as well to perform a least-squares fit. The heavy atom coordinates determined from these two methods are in good agreement. The newly measured moments of inertia of the heavy atoms has allowed for a refinement of the structure determined by an earlier microwave study. The conformation of 3-aminopropanol is stabilized by an intramolecular hydrogen bond from the alcohol proton to amino nitrogen. The experimental structure is consistent with the lowest energy ab initio [MP2/6-311++G(d,p)] structure.