Energetics and Structures of Adamantane and the 1- and 2-Adamantyl Radicals, Cations, and Anions

Abstract

Equilibrium structures and harmonic vibrational frequencies were computed for adamantane (Ad), the 1- and 2-adamantyl radicals (1-Ad•, 2-Ad•), cations (1-Ad+, 2-Ad+), and anions (1-Ad-, 2-Ad-). Ionization potentials and electron affinities of Ad, 1-Ad• and 2-Ad• have been predicted using four different density functional and hybrid Hartree−Fock/density functional methods. The equilibrium structure of adamantane (Td symmetry) is in excellent agreement with electron diffraction experiments. 1-Ad• and 1-Ad- are predicted to lie about 4 kJ mol-1 below their 2-isomers, while 1-Ad+ is predicted to lie 47 kJ mol-1 below 2-Ad+. For 1-Ad•, 1-Ad+, and 1-Ad-, C3v structures are found to be the minima, while a Cs structure lies lowest for 2-Ad•, 2-Ad+, and 2-Ad-. The final predicted adiabatic ionization potentials for the radicals are 6.22 (1-Ad•) and 6.70 eV (2-Ad•). The vertical radical ionization potentials are necessarily larger: 6.85 (1-Ad•) and 7.08 eV (2-Ad•). The predicted adiabatic electron affinities are a...