Ylide stabilized carbenes: a computational study

High‐level Density Functional Theory calculations, coupled with appropriate isodesmic reaction, are employed to investigate the effects of α‐carbon, ammonium, phosphorus, and sulfur ylides, cyclization , and unsaturation on the stability, multiplicity, and reactivity of novel singlet (S) and triplet (T) carbenes. Among them the highly π ‐donating α ‐ammonium ylide is found to exert the highest stabilizing effect on the carbenic center. α ‐Ammonium ylides resist dimerization and hydrogenation . They show wider singlet–triplet energy gap (Δ Ε S–T ), broader band gap (Δ Ε HOMO–LUMO ), and higher nucleophilicity compared to the reported stable  N ‐heterocyclic carbenes. Aromatic cyclic unsaturated ammonium, phosphorus, and sulfur ylide carbenes appear more stable than their saturated cyclic analogs which are in turn more viable than their acyclic counterparts. Copyright © 2014 John Wiley & Sons, Ltd.