On the conformational equilibrium of glycolamide: A free jet millimetre-wave spectroscopy and computational study

Abstract

The conformational equilibrium of glycolamide has been investigated by free jet rotational absorption spectroscopy in the frequency range 60–78.3 GHz and density functional calculations (B3LYP/aug-cc-pVTZ). The spectra show two conformers having C_s symmetry, with the hydroxyl syn or anti with respect to the carbonyl group. Also the rotational spectra of two vibrational satellites of the lower energy syn conformer have been assigned (ω_NH2, δ_C–C–O). From relative intensity and dipole moment measurements the energy difference between the vibrational ground states of the two conformers (E_anti − E_syn) has been estimated to be about 4 kJ mol⁻¹, this value compares with the calculated one, ΔE_DFT ≈ 3 kJ mol⁻¹. The nitrogen quadrupole coupling constants have been measured for both species: χ_aa = 2.3 (2) and 1.7 (2) MHz, χ_bb − χ_cc = 5.8 (1) and 5.6 (1) MHz for the syn and the anti conformer respectively.