Crystal and Molecular Structure of 1-Azabicyclo[3.3.3]undecane Hydrochloride. Correlation of Some Molecular Dimensions with Spectroscopic Properties

The crystal structure of the hydrochloride salt of 1-azabicyclo[3.3.3]undecane has been determined on the basis of 1664 nonzeoo intensities measured on a diffractometer. The crystals are triclinic with a = 10.830 (8) Å, b = 7.122 (6) Å, c = 7.014 (3) Å, a = 97° 58′ (4′), β =90° 24′(4′), and γ = 96° 17′(4′). The space group is and there are two molecules of C₁₀H₂₀NCl in the unit cell. The structure, including hydrogen atoms, has been refined by full-matrix least-squares methods to an R factor of 0.047. The cation has effective but noncrystallographic C₃ symmetry. The three constituent eightmembered rings are in the boat-chair (BC) conformation with the detailed geometry being a compromise between torsional, bond angle, and transannular H—H nonbonded effects. The C–C–C, C–N–C, and N–C–C bond angles are all increased above tetrahedral values. The large angles in the cation can be correlated with the uv spectrum and J¹³_C–H coupling constant at the methine carbon atom of the free base. There is an N⁺–H—Cl^– hydrogen bond of length 2.978 (3) Å.