The results obtained from CASSCF-MRMP2 calculations are used to rationalize the singlet complexes detected under matrix-isolation conditions for the reactions of laser-ablated Zr(3F) atoms with the CH3F and CH3CN molecules, without invoking intersystem crossings between electronic states with different multiplicities. The reaction Zr(3F) + CH3F evolves to the radical products ZrF· + ·CH3. This radical asymptote is degenerate to that emerging from the singlet channel of the reactants Zr(1D) + CH3F because they both exhibit the same electronic configuration in the metal fragment. Hence, the caged radicals obtained under cryogenic-matrix conditions can recombine through triplet and singlet paths. The recombination of the radical species along the low-multiplicity channel produces the inserted structures H3CZrF and H2CZrHF experimentally detected. For the Zr(3F) + CH3CN reaction, a similar two-step reaction scheme involving the radical fragments ZrNC· + ·CH3 explains the presence of the singlet complexes H3CZrNC and H2CZr(H)NC revealed in the IR-matrix spectra upon UV irradiation. © 2014 Wiley Periodicals, Inc.