The 14 N nuclear quadrupole hyperfine structures in the rotational spectra of acetamide, CH 3 CONH 2 , and α-fluoroacetamide, FCH 2 CONH 2 , have been resolved. From the observed patterns, the quadrupole coupling constants have been determined with high precision. The results provide evidence of considerable derealization of the nitrogen lone electron pair. For acetamide, the full coupling tensor has been determined from a combined analysis of the ground and first excited state of the methyl group internal rotation. The spectrum of α-fluoroacetamide-[ 15 N] has been obtained for the first time, and a refined structure is proposed.