Microwave Spectrum of Pivalaldehyde

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Abstract
The microwave spectrum of pivalaldehyde [(CH3)3CCHO] has been investigated in the frequency region 9–40 kMc/sec. The ground state, first and second excited states of the t-butyl torsion, and the first excited state of each of the three methyl torsions have been assigned. The barrier to internal rotation of the t-butyl top has been calculated from the splittings in the first excited state to be 1186 cal/mole, from the splittings in the second excited state to be 1176 cal/mole, and from the intensities of the first excited state relative to the ground state to be 1100 cal/mole. The excited states of the methyl torsions show no splittings, but the relative intensities yield barrier estimates of 2600, 3500, and 3800 cal/mole, if one assumes that the three tops are independent. On the basis of certain analogies with previously investigated molecules the lowest of these three barriers is very tentatively assigned to a methyl group which is eclipsed with respect to the oxygen atom. The dipole-moment components were computed from Stark-effect measurements to be μa=2.56 D and μb=0.76 D.