Trends in the proton nuclear magnetic resonance spectra of some amine-haloboranes. Steric effects

Article abstract of DOI:10.1021/ic50154a002

Borane adducts of trimethylamine and diethylamine were halogenated using free halogens or hydrogen halides, and the proton NMR spectra of these amine-haloborane adducts were obtained. The resonances of these adducts showed a shift to lower field with increased size of halogen or with increased number of halogens on boron. This shift to lower field had been previously attributed to inductive effects, but in this work it was shown that the shift to lower field was due to steric interaction between halogens on boron and alkyl groups on nitrogen. Proton NMR spectra for diethylamine-haloboranes were complex and showed patterns attributable to nonequivalent methylene protons. Computer analyses of the spectra allowed assignments consistent with preferred rotational configurations.