Effects of alkyl substitution on ionization energies of alkanes and haloalkanes and on heats of formation of their molecular cations Part 2.* Alkanes and chloro-, bromo- and iodoalkanes

Abstract

The adiabatic ionization energies (IEs) of alkanes and their halogen derivatives have been correlated using the following equation: IE(RX) = IE(XC(CH 3) m H 3− m ) − f(γ +). Here f(γ +) = 0.14γ + + 0.25 eV for X = H and m = 2 or 3, f(γ +) = 0.14γ + for alkanes containing a quaternary carbon atom, and f(γ +) = 0.16γ +, 0.10γ + or 0.05γ + for X = Cl, Br or I respectively, and γ + is the total number of carbon atoms at and beyond the γ-position with respect to the α-carbon atom closest to the site of the formal charge in the molecular cation. The average deviations between estimated and observed values are less than 0.08 eV for 22 hydrocarbons and 0.04 eV for 34 monohaloalkanes. The heats of formation these odd-electron cations have been estimated and are compared with values from the equations of Holmes . [Can. J. Chem., 59 (1981) 80]. The differences in the localization of the formal charges in the different cations have been discussed.