The electronic structure and geometry of CH₃F^– ion is calculated by the CNDO molecular orbital method and the results calibrated by parallel calculations on CH₃F. The C—F equilibrium distance increases by a very small amount (0.031 Å) on addition of an electron to CH₃F. The half-occupied orbital in CH₃F^–(in Unrestricted Hartree-Fock approximation) is antibonding between the carbon and fluorine, but bonding between fluorine and the hydrogens. The HCH angle is increased from 109·3 to 114·3° as a result of the increased F—H bonding. The negative charge of the anion is calculated to be distributed between the hydrogens and the fluorine, the carbon atom bearing a small positive charge.

The implications of these calculations for the mechanism of the electrochemical reduction of alkyl halide molecules, in which it has been postulated that the first electron-transfer step leads to formation of the molecular negative ion, is discussed. An interpretation of the observed trend of exchange rate constants for methyl halides is proposed. A similar interpretation for a series of substituted halides leads to the prediction that in complete electro-reduction of a particular stereoisomer, configurational inversion will be more complete the higher the atomic number of the halogen.

For the CH₃F/CH₃F^– exchange, the calculated energy of internal rearrangement in forming the transition state is small (< 1 kcal/mole). The possibility of complete calculation of the rate constants of a variety of electrode processes involving bond fission for which the primary step is of the type XY + e(M)→(XY)^– is discussed. It is concluded that this is now possible, using relatively simple methods of calculation, but that in order to locate the oxidation-reduction potential of the primary step, more detailed methods will need to be used to obtain the ground-state energy of the (XY)^– ions.