Substituent effect on electron affinity, gas‐phase basicity, and structure of monosubstituted propynyl radicals and their anions: A theoretical study

Abstract

The substituent effect of electron-withdrawing groups on electron affinity and gas-phase basicity has been investigated for substituted propynl radicals and their corresponding anions. It is shown that when a hydrogen of the alpha-CH(3) group in the propynyl system is substituted by an electron-withdrawing substituent, electron affinity increases, whereas gas-phase basicity decreases. These results can be explained in terms of the natural atomic charge of the terminal acetylene carbon of the systems. The calculated electron affinities are 3.28 eV (*C=C-CH(2)F), 3.59 eV (*C[triple bond]C-CH(2)Cl) and 3.73 eV (*C[triple bond]C-CH(2)Br), and the gas-phase basicities of their anions are 359.5 kcal/mol ((-):C[triple bond]C-CH(2)F), 354.8 kcal/mol (:C[triple bond]C-CH(2)Cl) and 351.3 kcal/mol ((-):C[triple bond]C-CH(2)Br). It is concluded that the larger the magnitude of electron-withdrawing, the greater is the electron affinity of radical and the smaller is the gas-phase basicity of its anion.

Insufficient Hartree–Fock Exchange in Hybrid DFT Functionals Produces Bent Alkynyl Radical Structures

“…This spurious bending was observed previously in calculations using the B3LYP XC functional. − Theoretical studies reporting bent 1-propynyl structures note that single-reference methods converge to a low-lying 2 E state, which is then subject to symmetry breaking and Jahn–Teller distortion. ,, Eisfeld demonstrated the need for detailed multireference configuration interaction calculations to obtain the correct ground state electronic structure of 1-propynyl . However, multireference effects cannot be fully responsible for bent geometries, as some single reference methods also predict linear R–C–C bond angles.…”