It is often possible to assign different resonance structures to an organometallic compound; for example, there can be competition between carbene and zwitterionic forms. Suggest ways of distinguishing the two forms and describe conditions that might favour one form over the other. See N. Ashkenazi, A. Vigalok, S. Parthiban, Y. Ben-David, L.J.W. Shimon, J.M.L. Martin, and D. Milstein, J. Am. Chem. Soc., 2000, 122, 8797; and C.P. Newman, G.J. Clarkson, N.W. Alcock, and J.P. Rourke, Dalton Trans., 2006, 3321.