High levels of ab initio and DFT calculations (B3LYP/6-311++ G**, B3LYP/AUG-cc-pVTZ, and CCSD(T)/6-311++G** levels) coupled with isodesmic reactions are used to compare and contrast the multiplicities and relative stabilities of singlet (s) and triplet (t) acyclic carbenes, including: dimethylcarbene, diaminocarbene, and diphosphinocarbene along with their saturated and unsaturated cyclic ones. Cyclization is unfavorable for all acyclic carbenes while unsaturation of cyclic analogs appears favorable. The simultaneous cyclization and unsaturation of dimethyl- carbene increases the singlet-triplet energy gap (δ£s-t), while for diphosphinocarbene the situation is reversed. For diaminocarbene the increase of δEs-t is encountered only during cyclization.
- Ab initio
- Isodesmic reaction