Planarity and low-energy vibrations of catecholborane: a microwave spectroscopic study

The rotational spectra of four isotopomers of catecholborane have been observed and measured in natural abundance in the frequency range 28–40 GHz. The molecule has been shown to be planar. The rotational spectra of three vibrational progressions have been measured for the most abundant isotopic species (11B). On the basis of the statistical weights and from the shifts of rotational constants with respect to the ground state they have been assigned to the butterfly, 1,3-ring twisting, and ring-puckering motions. The dipole moment has been measured to be 1.26(4) D (1 D ≈ 3.335 64 × 10–30 C m).