X-ray crystallog. for tricyclopropylamine (I) and its hydrochloride at 200 K showed that both have the same pyramidal structure at the N atom (? C-N-C=330.3 Deg) . Moreover the orientation of the three cyclopropyl groups with respect the lone pair nitrogen the neutral amine I and its salt is exactly the same as that detd. by microwave and computational studies on gas phase cyclopropylamine. A gas phase electron diffraction anal. structure anal. of I established that the mol. has the same conformation in the gas and liq. states. The vertical first ionization energy of I, detd. by HeI photoelectron spectra, was found to fall in line with dicyclopropylisopropylamine, cyclopropyldiisopropylamine, and cyclopropyldiethylamine, as compared to triisopropylamine. g- Radiation of I in CF2ClCFCl2 matrix at 77 K led to an anisotropic ESR spectrum of the I.bul.+ with planar geometry. UB3LYP/6-31G(D) calcns. indicate a min. energy geometry for the radical cation with C3h symmetry,17.0 kcal mol-1 more stable than a planar C3v geometry, with the three bicyclopropyl groups in the bisected orientation. Thus, the computational results, along with the ESR data, disclose a dramatic conformational difference between I and its radical cation.