Why Is the Diels-Alder Adduct between Difluorocyclopropenone and 1,3-Diphenylisobenzofuran So Reactive? An ab Initio Molecular Orbital Study of the Ring Opening of cis-2,3-Difluorocyclopropanone

Ab Initio Calculations on Heteroatomic Systems Using Density Functional Theory and Diffuse Basis Functions

“…We located the minima called conformation 1 and conformation 16 by Salzner and Bachrach, which we call 8 and 9 , respectively. Our results at the HF/6-31G(d) level are the same as reported;9f our MP2/6-31G(d) results differ very slightly because we did not reoptimize the geometry. The effect of diffuse functions to relatively lower the energy of 9 is seen at the HF and MP2 levels; the effect is slightly larger than what is gained by going from MP2 to QCISD(T).…”

“…This reaction has also been applied to cyclopropane ( 3 ) and trisilacyclopropane ( 4 ), yielding SE's of 28.7 kcal/mol and 38.9 kcal/mol, respectively, at the HF/6-31G(d) level . Our results, shown in Table , demonstrate that correlation energy is not an issue for 3 , but inclusion of diffuse functions has a small effect, consistent with “pseudo-π” bonding in 3 , which brings the calculated SE very close to the experimental value. , For 4 , correlation decreases the apparent SE by 3 kcal/mol; the lack of a diffuse function effect may be related to the imputed lack of “bent bonding” in 4 9b. For the DFT approach, a very small correlation effect is seen for 1 , along with a somewhat larger effect of diffuse functions.…”

“…It is generally understood that diffuse functions on heavy atoms are important for the proper description of anions, although they were found to be unnecessary in one recent study . For heteroatomic systems, particularly when lone pairs are present, diffuse functions are occasionally used, but often omitted . As concerns DFT (with non-local corrections), Houk's group has shown its efficacy in the study of pericyclic reactions, although it does have some limitations .…”

“…As concerns DFT (with non-local corrections), Houk's group has shown its efficacy in the study of pericyclic reactions, although it does have some limitations . Although its use appears to be growing, ,8a,9e, it does not seem generally clear that this methodology may be superior, in estimating correlation energies, to MP2 or even MP4 approaches. A poignant example is that of propargylene .…”

Cyclopropenylium Cations, Cyclopropenones, and HeteroanaloguesRecent Advances

“…The Diels-Alder reaction between difluorocyclopropenone and 1,3-diphenylisobenzofuran produced two 1:2 adducts (322 and 323) in a 9:1 ratio (eq 181). 294 The attempt to observe the monoadduct 320 at low temperature by NMR was not successful, which can be understood by considering that the initially formed monoadduct 320 underwent ring opening to zwitterion 321 faster than it was formed and that 321 reacts quickly with the second molecule of diphenylisobenzofuran. This is in contrast to the reaction of the parent cyclopropenone with 1,3-diphenylisobenzofuran (eq 180), which quantitatively yielded the stable monoadduct 318.…”