The out,out to out,in Transition for 1,(n+2)-Diazabicyclo[n.3.1]alkanes

Hexahydropyrimidines N,N-bridged by a chain of n methylene groups (1,(n+2)-diazabicyclo[n.3.1]alkanes) adopt out,out (axial,axial) structures for n=2, 3, and 4. When n=5, the photoelectron spectrum shows evidence of the presence of some of the out, in (axial,equatorial) isomer in the gas phase, although none can be found in solution. When n=6, the compound is apparently entirely out,in in the gas phase but exists as a mixture of out,out and out,in conformers in solution. For n=1, only the diamond lattice out,in isomer can be detected in solution. These experimental data are correlated with force field (MM2) calculations; multiple minimum search methods have been used to locate all low-energy conformations