Pars-Orbital-Methode (PO-MO), 2. Mitt.: Anwendung der Charakterordnungen aufDiels?Alder-Reaktionen

Theory of cycloaddition reactions

“…MO approaches to this problem first appeared in 19502 38 and have continued to appear up to the present. 203,210,211,223,[239][240][241][242][243][244] The most simplistic viewpoint assumes that energy of activation will parallel the heat of reaction, which in turn parallels the energy loss in the reaction.62,63 The 7r-energy loss defines a reactivity index called the paralocalization energy, L14.238,2 45 -247 Semiquantitative correlations of Lu and the rates of Diels-Alder reactions are well known.191,20 3,211,2 2 3 The rates of the maleic anhydride additions to five polycyclic aromatic hydrocarbons were recently determined,244 and the data are summarized in Table II. Localization energies were calculated for either attack at the single most reactive positions (L), or for simultaneous attack at the most reactive 1,4 position (Lu) using a semiempirical SCF-MO method.…”

Possible role of charge-transfer complexes in cationic polar cycloaddition

“…Konovalov33 et al have shown that there is a linear relationship between the rates of reaction of a series of N-arylmaleimides and their abilities to form charge-transfer complexes with , , ', ' -tetramethyl-p -phenylenediamine, and Tyutyulkov and Markov 34 from LCAO-MO calculations, have shown that a complex is formed between maleic anhydride and various condensed aromatic hydrocarbons and that a correlation exists between the delocalization energy of the complex and the corresponding values for Brown's para-delocalization energy, which is in turn a useful measure of Diels-Alder reactivity. 35 One of the most important recent theoretical developments in connection with cycloaddition has been the application of the frontier orbital approach.36-39 This method has been used successfully to account for reaction rates and regioselectivity by considering the interaction of the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor. It is pertinent that consideration of the same type of HOMO-LUMO interaction has been used successfully in explaining the formation of charge-transfer complexes.…”

Facile Synthesis of Janus “Double-Concave” Tribenzo[a,g,m]coronenes

“…Tribenzo[ a , g , m ]coronene 2 was first reported in 1968, synthesized from o,p,o,p,o,p -hexaphenylene . However, a poor yield, long synthetic route, and difficulties in selective modification limited its investigation further.…”