A survey of strained organic molecules

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

“…Thus, in this case, single-electron ionization is less costly and the difference in Koopmans' ionization energies works towards the increasing basicity of 5, which together with second largest relaxation energy of all compounds investigated here, makes this molecule the strongest base within this family of molecules (1)(2)(3)(4)(5). At the end, it is useful to emphasize that triadic analysis clearly reveals not only that the correct trend in basicity of systems 2-5 cannot be explained by considering only the features of initial bases, but also that, in all four cases, both properties of different states and their diverse relative significance are factors governing their basicities.…”

“…28,34,35 Proper insight into the mentioned intrinsic effect is important, since strain relief on protonation can have major impact on the basicity of strained compounds. For example, this was clearly demonstrated by Abboud, Koppel and co-workers, 36 who employed modified G2(MP2) approach to calculate the gas-phase basicity (GB) of cubane, C 8 H 8 , to be as large as GB = 258.8 kcal mol -1 , and attributed pronounced basicity to the formation of the rearrangement product, namely tetracyclo[4.2.0.0 2,4 .0 3,8 ]oct-7-ylium cation, created after strain relief and the opening of the rigid framework of cubane upon protonation. However, their calculated GB value differed by about 60 kcal mol -1 from that measured experimentally, 37 suggesting that the latter value, determined by FT-ICR mass spectrometry, does not correspond to the reversible protonation of cubane and that the proposed cation is not the final protonation product.…”

Electrostatic Potentials: A New Method for Interpreting and Predicting Molecular Reactivities and for Designing Synthetic Pathways. Applications to Nitroaromatics, Nitramines and Nitrated

“…For instance, as mentioned above, the indices for triprismane show that it has two cyclopropane-like and three cubane-like faces. And indeed, taking twice the strain energy of cyclopropane plus 3/6 times that of cubane ( which has six faces) actually gives a result P that is close to the strain energy of tr'prismane [13). Results and discussions of bond deviation index calculations have also been included in several others of our publications, listed elsewhere in this report.…”

Tandem Cyclization‐Cycloaddition Reactions of Rhodium Generated Carbenoids from α‐Diazo Carbonyl Compounds.

“…The formation of less strained five-membered ring ylides is generally favored compared to other ring sizes. 28 The generation of intramolecular five-membered ring carbonyl ylide intermediates in the presence of metal catalyst can be achieved with a variety of carbonyl-bearing precursors such as ketones, esters and amides. The successful trapping of such five-membered ring carbonyl ylides depends on the substrate structure and the absence of competition from alternative intramolecular reaction pathways.…”