Three-dimensional intramolecular dynamics: Internal rotation of (CH3)3GeBr

The microwave spectra of (CH3)374Ge79Br and its isotopologues (CH3)372Ge79Br and (CH3)374Ge81Br have been studied in the frequency range from 2.4-20 GHz revealing the complex internal dynamics of this organometallic molecule with three internal rotors. The assignment of the complex spectrum has been facilitated by permutation-inversion theory - the appropriate molecular symmetry group is G162. The V3 barrier to internal rotation is determined to be 4.783(12) kJ/mol. An analysis of the bromine quadrupole coupling yields the description of the Ge-Br and the Ge-C bonding characters. From this analysis we find that the bromine atom has a positive partial charge resulting from π-backbonding of the bromine towards germanium. From isotopic substitution, the Ge-Br bond distance could be determined to 2.34589(21) Å.