Nuclear hyperfine structure in the donor-acceptor complexes (CH3)3N-BF3 and (CH3)3N-B(CH3)3

► Rotational spectra of (CH3)3N−BF3 and (CH3)3N−B(CH3)3 have been observed in a jet. ► Quadrupole coupling constants for 10B, 11B, and 14N have been obtained. ► In both complexes, (CH3)3N donates ∼0.4 electrons to the donor-acceptor bond.