Heat of formations and group interactions of polydifluoroaminoadamantanes: First-principle predictions

Both the heats of formation (HOFs) and the group interactions were predicted for a series of adamantane derivatives substituted with difluoroamino groups by using density functional theory (DFT) with 6-31G∗ and 6-311G∗∗ basis sets. The adamantane skeleton was chosen for as a reference compound in the isodesmic reactions designed for calculating the HOFs. The contribution of difluoroamino group to the heat of formation deviates from group additivity. The relationship between HOFs and molecular structures was discussed. It was found that the HOFs decrease more with each difluoroamino group attached to the tertiary carbon than to the secondary carbon of the adamantane skeleton, when the secondary carbon was substituted by one group only. However, the HOFs increase with the second difluoroamino group attached to the secondary carbon. The distance between difluoroamino groups influences the values of HOFs. The group interacting energies of polydifluoroaminoadamantane increase in the range of 8-70 kJ/mol with each difluoroamino group attached. The interaction of neighbor difluoroamino groups discords with the group additivity. The relative stability of the title compounds was assessed based on the calculated HOFs, the energy gaps between the frontier orbitals, and the bond order of CNF2. The CNF2 bond is greatly weakened with two NF2 groups being attached to the same secondary carbon. The basis sets influence the HOFs when the substituent number is over 6 or when two substituted groups being attached to the same secondary carbon.