In this research, we are investigating oxonium ylides or complexes formed by interactions of singlet carbenes with water, selected alcohols, and dimethylether at the RHF and MP2 levels of theory using 3-21G, 6-31G*, and 6-311G** basis sets. The specific carbenes that we are studying include singlet methylene and singlet carbomethoxycarbene, CHCO2Me. Carbomethoxycarbene was chosen because it is similar to one of the carbenes studied experimentally, carboethoxycarbene. Alcohols chosen for this study include methanol and 2-methyl-3-buten-2-ol, an allylic alcohol employed in the experimental portion of this research.
Previous theoretical work on oxonium ylides and complexes has focused primarily on the interaction between water and methylene [1-3]. Eades et al. reported ab initio calculations on the H2O-CH2 ylide at the Hartree-Fock level using a basis set of double zeta plus polarization quality . Pople and coworkers  carried out calculations on H2O-CH2 using higher levels of theory (MP4/6-31G*//RHF/6-31G*). They report that although H2O-CH2 is a local minimum on the potential energy surface at the RHF/6-31G* level, it is unstable relative to methanol when electron correlation and corrections for zero point energies are included. Yates et al. determined optimized geometries and relative energies for H2O-CH2 at even higher levels of theory (MP4/6-311G**//MP2/6-31G*) . At this level, they find that a barrier for rearrangement of H2O-CH2 to methanol exists, but is only 1 kcal/mol. Similar structures to those obtained for CH2 interacting with H2O were also found at the MP2/3-21G level for CCl2 and CF2 interacting with H2O .
In addition to studying the structure and energetics of oxonium ylides or complexes formed between singlet carbenes and alcohols or ethers, we are investigating the reactivity of the complexes by determining transition states and intermediates along the reaction path for the addition of the carbene complex to ethene. One theoretical investigation of the mechanism for addition of H2O-CH2 to ethene has been reported . At the RHF/3-21G level, it was found that the reaction path for addition to a double bond is significantly different for H2O-CH2 than for the free carbene. The exothermicity of the reaction decreases from 93.1 kcal/mol for the reaction with singlet methylene to 72.8 kcal/mol for the reaction with H2O-CH2. Another striking difference is that an intermediate and transition state are found in the reaction of H2O-CH2 with ethene, while the energy decreases monotonically from reactants to products in the reaction of CH2 with ethene. From single point calculations including electron correlation , it is not clear whether the intermediate and transition state exist at higher theory levels.
Preliminary results of ab initio calculations on the carbene-water, carbene-methanol, and carbene-dimethylether complexes at the RHF and MP2 levels are presented in this poster. In addition, we also report results of ab initio calculations on carbene-2-methyl-3-buten-2-ol complexes. At the levels of theory employed, we find evidence for the formation of oxonium ylide-like complexes between the carbenes and the oxygen-containing compounds. We also find evidence for the formation of some interesting hydrogen-bonded complexes. Preliminary studies of the reaction paths for addition of some of the carbene complexes to ethene are also reviewed.