The structure of methyl fluoroformate from microwave spectroscopy and AB initio calculations

Abstract

The microwave spectra of three isotopic species of methyl fluoroformate, CD 3OCFO, CD 2HOCFO and CH 3 18OCFO have been measured and assigned. A barrier to internal rotation of 372±2 cm −1 has been obtained for three symmetric internal rotor species from internal rotation analyses. The rotational constants from five isotopic species have been used to determine an r 0 structure for the s- trans conformer (methyl group trans to fluorine). The s- cis conformation is not compatible with the experimental data as the data lead to an unrealistically large COC angle. The fully optimized structure from ab initio calculations with the 6-31G* basis set which include electron correlation at the MP2 level is compared with the experimental structure and with earlier results from RHF/6-31G* calculations.