CRYSTAL AND MOLECULAR-STRUCTURES OF 2,6-CIS-DIMETHYLPIPERIDYL-N-PHENYLACETAMIDINE AND 2,6-CIS-DIMETHYLPIPERIDYL-N-PHENYL-2,2-DIMETHYLPROPIONAMIDINE - X-RAY CRYSTALLOGRAPHIC INVESTIGATION OF THE C(SP2)-N(PIPERIDYL) BOND

The single crystal X-ray analyses of 2, 6-cis-dimethylpiperidyl-N-phenylacetamidine (MA) and 2, 6-cis-dimethylpiperidyl-N-phenyl-2, 2-dimethylpropionamidine (TBA) are described. MA crystallizes in the space group P2 1c with four molecules in the unit cell of dimensions a = 10.238 (2), b = 10.189 (2), c = 12.875 (3) Å. and β = 95.82 (2)°. The structure was solved and refined from 1401 unique observed reflections collected on an automated four-circle diffractometer to final values of the discrepancy indices of R = 0.046 and Rw = 0.058. TBA crystallizes in the space group P21c with eight molecules in the unit cell of dimensions a = 8.470 (2), b = 16.095 (3), c = 24.900 (4) Å, and β = 96.29 (2)°. From 2633 unique observed reflections similarly collected the structure was solved and refined to final values of the discrepancy indices of R = 0.061 and Rw = 0.074. The structure analyses show, in agreement with 13C NMR spectroscopic data, that ihe two molecules adopt different conformations around the C(sp2)-N(piperidyl) bond, the amidinic group and the piperidyl ring being approximately coplanar in MA and orthogonal in TBA, respectively. The comparison of the present data with the data in the literature, supported by nonbonded intramolecular potential energy calculations and IN DO calculations, allows clarification of the relationship among the torsion angle around the C-N bond, the bond distances in the amidinic group, the pyramidality of the N (piperidyl) atom and the conformation of the 2, 6-m-methyl groups in the piperidyl ring. © 1979, American Chemical Society. All rights reserved.