title: Computational investigation of the competition between the concerted Diels-Alder reaction and formation of diradicals in reactions of acrylonitrile with nonpolar dienes.
abstract: The energetics of the Diels-Alder cycloaddition reactions of several 1,3-dienes with acrylonitrile, and the energetics of formation of diradicals, were investigated with density functional theory (B3LYP and M06-2X) and compared to experimental data (Hall et al., J. Org. Chem.1993, 58, 7049-7058). For the reaction of 2,3-dimethyl-1,3-butadiene with acrylonitrile, the concerted reaction is favored over the diradical pathway by 2.5 kcal/mol using B3LYP/6-31G(d); experimentally, this reaction gives both cycloadduct and copolymer. The concerted cycloaddition of cyclopentadiene with acrylonitrile is preferred computationally over the stepwise pathway by 5.9 kcal/mol; experimentally, only the Diels-Alder adduct is formed. For the reactions of (E)-1,3-pentadiene and acrylonitrile, both cycloaddition and copolymerization were observed experimentally; these trends were mimicked by the computational results, which showed only a 1.2 kcal/mol preference for the concerted pathway. For the reactions of (Z)-1,3-pentadiene and acrylonitrile, the stepwise pathway is preferred by 3.9 kcal/mol, in agreement with previous experimental findings that only polymerization occurs. M06-2X is known to give more accurate activation and reaction energetics (Pieniazek, et al., Angew. Chem. Int.2008, 47, 7746-7749), but the energies of diradicals are too high.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA.
authors.forename: Natalie C
authors.initials: NC
authors.lastname: James
authors.forename: Joann M
authors.initials: JM
authors.lastname: Um
authors.forename: Anne B
authors.initials: AB
authors.lastname: Padias
authors.forename: H K
authors.initials: HK
authors.lastname: Hall
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
mesh_terms: D000181:Acrylonitrile / Q000737:chemistry*; D000466:Alkadienes / Q000737:chemistry*; D003500:Cyclization; D005609:Free Radicals / Q000138:chemical synthesis / Q000737:chemistry; D015394:Molecular Structure; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D000466:Alkadienes; D005609:Free Radicals; D000181:Acrylonitrile