Conformational study of N acyl r-2 c-4 diphenyl 3 azabicyclo[3.3.1]nonanes and N₃,N₇ diformyl r-2,c-4,t-6,t-8 tetraphenyl 3,7-diazabicyclo[3.3.1]nonane by NMR spectroscopy and semi-empirical molecular orbital calculations

110-119The stereochemistry and stereodynamics of N chloroacetyl and N benzoyl-r 2,c 4 diphenyl 3 azabicyclo[3.3.1]-nonanes (7 and 8) and N₃,N₇ diformyl r 2,c 4,t 6,t 8-tetraphenyl 3,7 diazabicyclo[3.3.1]nonane 11 have been studied using NMR spectral techniques and semi-empirical calculations. The N chloroacetyl and N benzoyl r 2,c 4 diphenyl 3 azabicyclo- [3.3.1]nonanes (7 and 8) prefer twin chair conformations with a slight flattening at the nitrogen end. In case of N₃,N₇-diformyl derivative 11, the preferred conformation is twin chair with flattening at both the nitrogen ends in which two of the phenyl groups at C2 and C4 occupy axial positions and two of the phenyl groups at C6 and C8 occupy quasi axial positions. The energy barrier for the N CO rotation in N₃,N₇ diformyl derivative 11 has been determined from the dynamic ¹H NMR spectral studies and it is found to be 70.4 kJ mol⁻¹. The results obtained from solution state for the N-acyl derivatives 7, 8 and 11 are well supported by the results from semi-empirical molecular orbital calculations