Knowledge Bank

The microwave spectrum of pivalaldehyde, $(CH3)3CCHO1$ has been investigated in the 9-40 Gc region. The ground state, first and second excited states of the tertiary butyl torsion and the first excited torsional state of each of the three methyl groups have been assigned. The barrier to internal rotation of the tertiary butyl top has been calculated from the splittings of the first excited state to be 1186 cal/mole, from the splittings of the second excited state to be 1170 cal/mole and from the intensity 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 2720 cal/mole, 3690 cal/mole and 3890 cal/mole, if one assumes that the three tops are independent. The dipole moment components were computed from Stark effect measurements to be $\mu a=2.56D$ and $\mu b=0.76D$.