Evidence for hydrogen-bond enhanced structural anomeric effects from the protonation of two aminals, 5-methyl-1,5,9-triazabicyclo[7.3.1]tridecane and 1,4,8,11-tetraazatricyclo[9.3.1.1 4,8]hexadecane

Synthesis and structural studies of a new class of quaternary ammonium salts, which are derivatives of cage adamanzane type aminal 1, 3, 6, 8-tetraazatricyclo[4.3.1.13,8]undecane (TATU)

“…Molecular orbital studies at the ab initio level implicate (n N →σ* C-N ) type interactions between a lone pair on N and an antiperiplanar σ* orbital of the adjacent C-N bond as being responsible for the anomeric effect [ 9 ]. In fact, in N-protonated aminals, the existence of a strong anomeric effect has been clearly established [ 10 , 11 ]. Our results suggest that the anomeric effect evidenced by the shortening and lengthening of N-C-N bond lengths and distortion of the C-N-C bond angles increases the p character of non-charged nitrogens and reduces the N-pyramidality, thereby making the nitrogen less nucleophilic [ 12 ].…”