The molecular structure and conformational and rotational composition of 3,7,9-tris(trifluoromethylsulfonyl)-3,7,9-triazabicyclo[3.3.1]nonane1have been investigated by synchronous gas-phase electron diffraction/mass spectrometry GED/MS and theoretical calculations (B3LYP and M06-2X with cc-pVTZ and aug-cc-pVTZ basis sets) and compared to the X-ray structure. All 16 possible conformers and rotamers were calculated, differing by the conformations of the two piperazine rings, orientation of the CF3groups relative to these rings, and non-equivalence of the two wings of the butterfly structure. The optimized geometry of the most stable1-c-out-2-c-outconformer coincides with that in the crystal. In contrast to only one conformer determined by X-ray, the GED analysis revealed the presence of five conformers,1-c-out-2-c-out(I),1-c-in-2-c-out(II),1-c-out-2-c-in(III),1-b-out-2-c-out(IV),1-c-out-2-b-out(V) in the ratio ofI:(II+III):IV:V= 36(10):42(6):22(10):0(10). The experimental results are better reproduced by calculations performed for 428 K (the temperature of the GED experiment) than for 298 K (standard), and most satisfactorily at the M06-2X/aug-cc-pVTZ level of theory.