MICROWAVE-SPECTRUM, CONFORMATION, INTRAMOLECULAR HYDROGEN-BONDING ANDAB-INITIO CALCULATIONS FOR 2-NITROETHANOL

The microwave spectrum of 2-nitroethanol has been investigated in the 26.5-39.0 GHz spectral region at room temperature. The spectra of the ground and of six excited states of the torsional vibration of the nit ro group of one rotamer were assigned and could be fitted to the ordin ary Watson Hamiltonian to within the experimental accuracy. The nitro group is not rotating freely but has a low torsional frequency determi ned to be 34(10) cm(-1) by relative intensity measurements. The identi fied conformer has a gauche arrangement for the O-C-C-N chain of atoms and is stabilized by a weak six-membered intramolecular O-H ... O hyd rogen bond formed between the hydrogen atom of the hydroxyl group and one of the oxygen atoms of the nitro group. The N-O bond (where the ox ygen atom is involved in intramolecular hydrogen bonding), and the C-C bond are about 17 degrees from being completely eclipsed. This rotame r is at least 4 kJ mol(-1) more stable than any other rotameric form o f the molecule. The microwave work has been assisted by ab initio comp utations made at the MP2/6-31 + + G* level of theory.