The variable temperature (1)H, (13)C, and (19)F NMR spectra were measured for the title N-nitrosamines. The observed unusually low N-N rotation barriers (12-15 kcal/mol) result from a significant deviation of the nitrosamino system from planarity. A pyramidal character of the amino nitrogen was confirmed by the X-ray crystal structures of two compounds and by bathochromic shifts of the n-pi absorption bands in the UV spectra. The nonplanarity of the nitrosamino moiety is due to the strong pseudoallylic A((1,3)) strain caused by the steric interaction of the NNO group with the neighboring aryl substituents fixed in the equatorial positions of the bicyclic skeleton. In addition, the barriers to the C-C rotation of aryl groups were examined at temperatures lower than required to "freeze" the N-N rotation and different DeltaG() values were observed for the aryls oriented syn and anti to the nitroso oxygen.
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