STRUCTURES AND MOLECULAR-PROPERTIES OF ST ERICALLY OVERCROWDED MOLECULES .43. TRIISOPROPYLAMMONIUM CHLORIDE - SINGLE-CRYSTAL STRUCTURE AND CALCULATIONS CONCERNING THE PROTONATION OF THE P-TYPE NITROGEN ELECTRON-PAIR

The protonation of triisopropylamine, which contains an almost planar NC3 skeleton of C3 symmetry and, therefore, a p-type N electron pair, with HCI in methanol causes severe structural perturbation due to extr eme steric overcrowdedness: the single-crystal structure determination (orthorhombic Pbca, Z = 8) proves that the molecular symmetry is redu ced to C(s) by the rotation of one isopropyl group around its CN axis by almost 90-degrees and the decrease of the angles CNC from 119-degre es each to 115, 115 and 111-degrees, respectively. The Cl- ... (H)N hy drogen bond distance of 315 pm is presumably slightly increased by ste ric overlap of the van der Waals radii of Cl- and one of the three adj acent methyl groups. The protonation of the p-type lone pair of triiso propylamine including the pyramidalization of the nitrogen centre and the twist of one isopropyl group can be simulated by a one-dimensional energy hypersurface calculation, if H+ attack outside the C3 axis is assumed.