Propargyl radical: an electron localization function study

Bonding in the C3H3 radical has been determined using the topological analysis of the electron localization function (ELF) calculated with various wavefunctions (HF, LSDA, MP2, CASSCF, QCISD, BLYP, B3LYP). Not only is ELF independent of quantum chemical approximation, but also produced topologically equivalent molecular partitions. The ELF partition of space into localization domains provides an objective characterization of bonding in C3H3, supporting a resonance description of almost equal contributions of propargyl and allenyl forms. Moreover, it explains the reported difference between the frequencies of the in-plane and out-of-plane bending modes (∠C(2)C(3)H(3)) arising from the topology of the C(2)C(3) bonding region.