Methylene-iodonium ylide: an isomer of diiodomethane

Iso-diiodomethane, H2CII is a minimum at the B3LYP/6–31G(d) and MP2/6–31G(d) levels and is separated from conventional isomer, diiodomethane, by a barrier of 134.6 kJ mol−1 calculated using G2 theory. The G2 calculated heats of formation for diiodomethane and iso-diiodomethane are 136.1 and 317.8 kJ mol−1, respectively. The enthapy change of the H2CII → H2CI + I(3P) dissociation is only 19.4 kJ mol−1. The charge distribution for H2CII does not agree with the description of this species as a hypervalent structure with a positive charge on the carbon and a negative charge on the central iodine.