Electron-Diffraction Study of the Structure of B(CH3)3

The molecular structure of gaseous B(CH3)3 was determined by the sector-microphotometer method of electron diffraction. Essentially free rotation of methyl groups was found. Mean bond lengths and standard errors were B–C=1.5783±0.0011 Å and C–H=1.1138±0.0015 Å. The angles CBC and BCH computed from mean distances, ignoring shrinkage effects, were 119.4°±0.3° and 111.9±0.2°, respectively. Shrinkage corrections would add roughly 0.5°. Root-mean-square amplitudes of vibration were lBC=0.0536±0.0012 Å, lCH=0.0811±0.0018 Å, lC···C=0.0762±0.0017 Å, and lB···H=0.1256±0.004 Å. Methyl groups differed significantly from CH3 groups in methane but not from methyl groups in ethane. Bond lengths and amplitudes provided no evidence for hyperconjugative stabilization.