Microwave spectra, barrier heights to internal rotation of methyl group, and dipole moments for conjugated chain compounds Methacrolein
The microwave spectrum of methacrolein, CH 2C (CH 3)CHO, was measured in the frequency region from 7.6-25 GHz. The R- and Q-branches for the a-type have been assigned and the rotational constants for the A-level are determined to be A = 8612.39 MHz, B = 4403.08 MHz, and C = 2965.33 MHz. All the Q-branch transitions observed have been split into doublets by the hindering rotation of the methyl group, and the barrier height has been determined to be 1340 ± 20 cal/mole by using the frequency splittings of these lines. The value of the total dipole moment is 2.80 ± 0.03 D, somewhat different from the value previously obtained by dielectric constant measurements.