The applicability of MCSCF gradient methods to the calculation of transition structures and diradicaloid intermediates is discussed. It is shown how the diabatic surface model provides a useful criterion for the choice of the valence space in the MCSCF method and also provides useful qualitative information about the electronic rearrangement associated with various transition states. These ideas are then applied to the synchronous and asynchronous 1,3-dipolar cycloaddition of fulminic acid to acetylene.