The nature of mercury—carbon bonds in mercury alkyl radicals

Values for the dissociation energy of the first mercury—carbon bond in mercury dimethyl and diethyl have been compared with the thermochemical values for the sum of the two bond energies in each molecule. With both molecules the energy required to break the first bond is very much larger than that required for the second. It is suggested that the bond energy data can only be interpreted satisfactorily on the basis that the bond in mercury alkyl radicals (and in mercury hydride) is predominantly a polarization bond. The polarization structure, for which the mercury atom is in a zero-valent state, is stabilized by resonance with an excited covalent structure which derives from a divalent state of mercury. The energetics involved in this suggestion have been discussed fully. The normal internuclear separation of the bond in these radicals has also been discussed. The potential energy curve representing the breaking of the first bond in mercury alkyl molecules has been examined in detail. It has been shown that, although a change in valence state of the mercury atom occurs during the rupture of the bond, the identification of the experimentally determined activation for this process with the bond dissociation energy is valid.