Microwave spectrum, structure, dipole moment, quadrupole coupling constants, and barrier to internal rotation of methoxyborane, CH 3OBH 2

Abstract

A short-lived boron compound, CH 3OBH 2, has been identified by microwave spectroscopy as an intermediate in the reaction of diborane with methanol or diborane with formaldehyde. The spectrum shows large splittings due to the internal rotation of the methyl top. An analysis of the spectrum by use of the principal axis method leads to the following parameters for the normal species: A = 50684.2(13) MHz, B = 10284.41(11) MHz, C = 9024.80(11) MHz, θ = 26.06(18)°, s = 15.983(5), I α = 3.226(11) u A ̊ 2 , and V 3 = 740(5) cal/mol. The hyperfine structure due to the 11B nuclear quadrupole moment has also been analyzed, and χ aa = −1.90(24) MHz, χ bb = −1.91(24) MHz, and χ cc = 3.81(22) MHz have been obtained. The total electric dipole moment determined for the normal species is μ = 1.61(10) D. The molecular structure has been determined from the rotational constants of 10B, 13C, CH 3OBD 2, CD 3OBH 2, and CHD 2OBH 2 species with the aid of an ab initio MO calculation.