On November 17, 2000, Manoharan, Mariappan; De Proft, Frank; Geerlings, Paul published an article.Electric Literature of 34413-35-9 The title of the article was Enhanced Aromaticity of the Transition Structures for the Diels-Alder Reactions of Quinodimethanes: Evidence from ab Initio and DFT Computations. And the article contained the following:
The Diels-Alder reactions of various quinodimethanes with ethylene are studied by means of ab initio MO and d. functional theory (DFT) to show the effect of aromaticity on the reaction path. The calculations reveal that these reactions are both kinetically and thermodynamically much more favored than the prototype butadiene-ethylene Diels-Alder reaction due to the aromatization process in the transition state (TS) and product. A progressive aromaticity gain is noticed during the reaction, and hence the partial π-delocalized peripheral diene ring function is coupled with the six-electron σ,π-delocalized cyclic unit resulting in an enhanced aromaticity of the TS. The magnetic criteria such as magnetic susceptibility exaltation and nucleus independent chem. shift provide definitive evidence for and fully support the aromatization process and the aromaticity of the TS. The extent of σ-π delocalization and the bond make-break at the TS are consistent with each other, and this is strongly influenced by the adjacent π-aromatization process. Moreover, the aromaticity trends in the resulting TSs and products parallel the activation and reaction energies; the extent of aromatization increases with increasing reaction rate and exothermicity. This confirms that aromaticity is the driving factor governing cycloadditions involving quinodimethanes. The experimental process involved the reaction of 5,6,7,8-Tetrahydroquinoxaline(cas: 34413-35-9).Electric Literature of 34413-35-9
The Article related to aromaticity transition state diels alder quinodimethane ab initio dft, Physical Organic Chemistry: Theoretical Organic Chemical Concepts, Including Quantum and Molecular Mechanical Studies and other aspects.Electric Literature of 34413-35-9
Referemce:
Quinoxaline – Wikipedia,
Quinoxaline | C8H6N2 | ChemSpider