Issue 3, 1999

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

Abstract

The structure of the monoprotonated ion, 2, of 5-methyl-1,5,9-triazabicyclo[7.3.1]tridecane, 1, as a picrate shows an NMeH+ group engaged in a transannular hydrogen bond with one of the aminal nitrogen atoms and this, in turn, induces a small but measurable structural anomeric effect in the aminal functional group. Diprotonation of 1 in CF3CO2H yields an equilibrium mixture of two isomeric bicyclic dications which are interconverted via a monocyclic ion containing a H2C[double bond, length half m-dash]N+ group and further protonation by CF3SO3H traps the iminium ion as a monocyclic trication. The structure of the monoprotonated ion, 4, of 1,4,8,11-tetraazatricyclo[9.3.1.1 4,8]hexadecane, 3, as a perchlorate shows the cation with effective C2 symmetry, a nearly linear, and almost symmetrical, transannular hydrogen bond, and a more pronounced structural anomeric effect in both hexahydropyrimidine units. Diprotonation of 3 gives a dication, 5, and the structure of the bis(trifluoroacetate) shows measurable shortening of the aminal C–NR2 bond in spite of the fact that the lone pair and the C–N+ bond are close to gauche. The structural effects in 2, 4, and 5 are well-reproduced by Becke–Perdew density functional theory calculations, and a natural bond orbital analysis of the parent system H3N–H+  · · ·  NH2CH2NH2, based on SCF and MP2 ab initio calculations is described.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1999, 589-599

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

R. W. Alder, T. M. G. Carniero, R. W. Mowlam, A. Guy Orpen, P. A. Petillo, D. J. Vachon, G. R. Weisman and J. M. White, J. Chem. Soc., Perkin Trans. 2, 1999, 589 DOI: 10.1039/A807954D

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