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, , 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 and . They show wider singlet-triplet energy gap (Δ ΕS-T), broader band gap (Δ ΕHOMO-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. [ABSTRACT FROM AUTHOR]