Rotational spectrum, conformation and dipole moment of 4-methyl-1,3-dioxane

The rotational spectrum of 4-methyl-1,3-dioxane, C5H10O2, has been recorded from 16.0 to 40.0 GHz. The a -, b- and c-type transitions with J <= 57 have been observed and assigned for the normal species in the ground vibrational state. The rotational constants and the quartic centrifugal distortion constants were determined to be A = 4802.335(2) MHz, B = 2376.163(1) MHz, C = 1738.852(1) MHz and Delta(J) = 0.1496(6) kHz, Delta(JK) = 0.157(5) kHz, Delta(K) = 0.76(3) kHz, delta(J) = 0.0423(1) kHz, delta(K) = 0.260(3) kHz. Stark effect measurements were used to determine the projections of the dipole moment on the principal inertial axes (in Debye units): mu(b) = 0.73(1), mu(b) = 1.32(1), mu(c) = 1.36(1) and mu(tot) = 2.03(2). Comparison of the experimental rotational constants and dipole moment components with results of ab initio calculations (B3PW91/aug-cc-pVDZ) shown that 4-methyl-1,3-dioxane exist in chair form with equatorial orientation of methyl group.