ECLIPSED GROUND-STATE CONFORMATIONS OF THE TERT-BUTYL-X BOND IN N-TERT-BUTOXY-2,2,6,6-TETRAMETHYLPIPERIDINE AND N-NEOPENTYL-2,2,6,6-TETRAMETHYLPIPERIDINE - X-RAY CRYSTAL-STRUCTURE DETERMINATIONS AND MOLECULAR MECHANICS CALCULATIONS

X-ray crystallographic studies of derivatives of N-methoxy- and N-tert-butoxy-2,2,6,6-tetramethylpiperidine show that as expected the N-O bond is staggered with respect to the C-H bonds of the methoxy group in the former case, yet it eclipses a C-methyl bond of the tert-butyl group in the latter case. Molecular mechanics calculations confirm this and show that likewise the preferred conformation of N-neopentyl-2,2,6,6-tetramethylpiperidine has the CH2 to tert-butyl group bond eclipsed, whereas in the corresponding N-ethyl compound the CH2 to methyl bond is staggered. Calculations of tetramethylcyclohexyl analogues and of axial conformations of all of these molecules are reported.