The isomerization of acetylene to vinylidene is examined theoretically in full dimensionality using a recent global potential energy surface. Eigenfunctions and eigenvalues of the exact Hamiltonian, for zero total angular momentum, are obtained using a series of truncation/recoupling procedures that begins with the eigenfunctions of a three degree-of-freedom Hamiltonian for the angular motion. By examining expectation values of the eigenfunctions a number of states are definitely identified with vinylidenelike characteristics.