Rotational spectra, structure, and electric dipole moments of methyl and ethyl tert-butyl ether (MTBE and ETBE)

The rotational spectra of methyl and ethyl tertiary butyl ether (MTBE and ETBE) have been observed and analyzed using a pulsed-molecular-beam Fabry-Perot cavity microwave spectrometer. Both a- and b-type transitions are observed for each compound. Small CH3 internal rotation splittings from the OCH3 group of similar to 1 MHz are observed for MTBE. The high sensitivity of the Fourier transform microwave (FTMW) technique allows observation and analysis of the rotational spectra of all C-13 isotopes and the O-18 isotopic species in natural abundance. For ETBE, the structural analysis indicates that the lowest energy form of the molecule is the completely extended conformer with C-s symmetry. For both compounds, the bulkiness of the t-butyl group causes the COC angle to be 6 degrees to 7 degrees larger than that found in most other ethers. (C) 1997 Academic Press, Inc.