The structural and conformational properties of 2-methoxyfuran as studied by microwave spectroscopy and quantum chemical calculations

Abstract

The microwave spectrum of 2-methoxyfuran has been investigated in the 10.0–60.0GHz spectral region at about −35°C. One rotamer denoted Syn was assigned. This conformer is at least 3kJmol−1 more stable than any other form. Syn has a symmetry plane (Cs symmetry). The methyl group is Syn to the nearest CC bond of the ring. The dipole moment components along the principal initial axes and the total dipole moment are (in units of 10−30Cmm): μa=3.62(16), μb=5.98(3), μc=0.0 (for symmetry reasons), and μtot=6.99(12). Four vibrationally excited states belonging to three different normal modes were assigned and their frequencies determined by relative intensity measurements. The barrier to internal rotation of the methyl group is at least 14kJmol−1.The microwave work has been assisted by quantum chemical computations at the MP2/6-311++G∗∗ (frozen core), B3LYP/cc-pVTZ and B3LYP/6-311++G∗∗ levels of theory. These rather advanced calculations were found to predict rather different conformations for a second conformer.