Computational study of aza-adamantanes as multivalent bases

Abstract

Structure and bonding characteristics, and gas phase stepwise basicities of proposed multivalent bases 1,3, 5,7-tetraazatricyclo[3.3.1.1(3,7)]decane, 1,3,5,7,9,10-hexaazatricyclo[ 3.3.1.1(3,7)]decane and tricyclo[3.3.1.1(3,7)] azadecane, named and abbreviated here respectively as tetra-aza-adamantane (TAA), hexa-aza-adamantane (HAA) and deca-aza-adamantane (DAA), have been studied using B3LYP/6-311++G** method. Effects of protonation on the bond lengths and angles, and atomic charges, and on their correlations are studied in detail. Results show that the most affected characteristics by protonation are the N- H bond lengths and the charge of the hydrogen atoms. It is found, interestingly, that in the protonation of DAA, electric charges of the unprotonated nitrogen atoms are increased more than that of the protonated nitrogen atoms. Because of very small effects of protonation on the skeletal C-N and N-N bond lengths, it can be said that the azaadamantane cage volume is not changed significantly upon protonation. The protonation energies approve multivalent nature of these bases with the order of TAA ≈ HAA> DAA. Different isomers for the unprotonated and protonated HAA and DAA are also studied. © Springer Science+Business Media, LLC 2012.