1. Diels-Alder Reactivities of Benzene, Pyridine, and Di-, Tri-, and Tetrazines: The Roles of Geometrical Distortions and Orbital Interactions.
- Author
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Yun-Fang Yang, Yong Liang, Fang Liu, and Houk, K. N.
- Subjects
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DIELS-Alder reaction , *BENZENE , *ORBITAL interaction , *REACTIVITY (Chemistry) , *PYRIDINE , *TETRAZINE , *RING formation (Chemistry) - Abstract
The cycloadditions of benzene and ten different azabenzenes (pyridine, three diazines, three triazines, and three tetrazines) with the ethylene dienophile have been explored with density functional theory (M06-2X) and analyzed with the distortion/interaction model. Activation barriers correlate closely with both distortion energies and interaction energies over an activation energy range of 45 kcal/mol. The replacement of CH with N increases Diels-Alder reactivity due not only to the more favorable orbital interaction, but also to a decrease in distortion energy. The rates of reactions are greatly influenced by the nature of the bonds being formed: two C--C bonds > one C--C bond, and one C--N bond > two C--N bonds. The activation energy of Diels-Alder reactions correlates very well with reaction energies and with the NICS(0) values of the aromatic dienes. The distortion energy of the Diels-Alder reaction transition states mostly arises from the diene out-of-plane distortion energy. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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