Jet cooled rotational spectrum of methyl lactate

We report here the measurements of the rotational spectra of the main, O-d and four 13C species of methyl-lactate. They have been obtained by free jet millimeter-wave absorption and molecular beam Fourier-transform microwave spectroscopy. Only lines of the most stable conformer, the one with the hydroxyl group acting as a proton donor to the carbonylic group oxygen, have been observed. The V3 barrier to internal rotation of the CH3–O methyl group has been determined to be 4.84(2) kJ mol−1. The experimental conformational and structural information are compared to those given by MP2/6-311++G(d, p) calculations.