Gas-phase versus crystal structure of triflamide and some of its heterocyclic derivatives

A gas-phase electron diffraction analysis combined with mass-spectrometry (GED/MS) of (2R,9S)-trans-2,9-diiodo-13-(triflyl)-13-azabicyclo[8.2.1]tridec-5-ene was performed and the results were compared with those studied earlier by GED/MS and X-ray analysis of triflamide derivatives, that is 3,7,9-tris(triflyl)-3,7,9-triazabicyclo[3.3.1]nonane, 6-iodo-3-(triflamidomethyl)-4-triflyl-1,4,2,7-oxazadisilepane, and 2,2,4,4-tetramethyl-6,8-bis(triflyl)-3-oxa-6,8-diaza-2,4-disilabicyclo[3.2.2]nonane. In addition, the first GED study was performed for triflamide CF₃SO₂NH₂, for which the X-ray structure has also been studied. Two conformers of the first compound with the oppositely distorted dihedral angles in the five-membered ring were identified in the gas phase, and, after careful analysis, also in the crystal. Very low barrier to interconversion (1.7 kcal mol^-1) and energy difference (0.6 kcal mol^-1) were calculated. In the gas phase, the S-N and S-C bonds are longer than in the crystal, clearly indicating tightening due to crystal packing effects.