Abstract The electronic structures of CH3C1 and a “transient” species (Cl…CH3…Cl)− have been calculated by an extended Hückel method. The calculated results of CH3C1 correlate well with the experimental facts. The main features of the electronic structure of (Cl…CH3…Cl)−-may be summarized as follows: 1) The 3py orbitals of the chlorine atoms and the 2py orbital of the central carbon atom (pσ-orbitals) play an important role in the interaction between the C–Cl bonds. 2) The 2s orbital of the central carbon atom at the symmetrical configuration makes no contribution to the C–Cl bonding; rather, this orbital, together with the 2px and 2pz orbitals, participates in the C–H bonding. 3) The 3px and 3pz orbitals of the chlorine atoms form the lone-pair orbitals. The natures of the MO’s of the symmetrical configuration have also been briefly discussed. It should be noticed, however, that the present treatment is not yet sufficiently qualified as a method to allow an interpretation of the stable configuration of a molecular system, since it does not explicitly take into account the nuclear repulsion and the electronic interaction. Accordingly, there remains room for criticism with respect to the theoretical significance which the configuration of such a local minimum will have in the true electronic process on the reaction path. This point will be examined further in the future.