Transition states and selectivities of singlet carbene cycloadditions

Molecular orbital studies of carbyne reactions: addition and insertion reaction paths for the reaction

“…This asymmetric approach 1s in line with the predictions of the molecular orbital studies of the reaction path for the addition of singlet ('A,) methylene to ethylene (37,38) favoring the asymmetric approach without any activation energy. Asymmetric reaction paths were also predicted for several singlet ('A,) substituted carbene cycloaddition reactions with some activation energy (37,39). The present computational results' prediction of a zero activation energy for the addition reaction of C H (~' I I ) to c 2 H 4 ( X 1~, ) compares well with the experimental value of -0.35 kcal mol-I recently reported by Berman, Fleming, Harvey, and Lin (2).…”

Finding the Transition State of Quasi-Barrierless Reactions by a Growing String Method for Newton Trajectories: Application to the Dissociation of Methylenecyclopropene and Cyclopropane

“…Quantum chemical calculations [30][31][32][33][34][35][36][37][38] have confirmed the early predictions based on either just electronic structure considerations or orbital (state) symmetry according to the Woodward-Hoffmann rules.…”

“…[28][29][30][31][32][33][34][35][36][37][38] Hoffmann and co-workers [29] demonstrated that the reaction of methylene and ethene is symmetry-allowed when the methylene follows a C s symmetrical non-linear (oblique) approach path whereas it is forbidden when the reaction complex possesses C 2v symmetry corresponding to a linear movement of methylene along the C 2 axis of the complex and leading to a T-structure where the top bar is the ethene molecule.…”

Distortion/interaction analysis of the reactivities and selectivities of halo– and methoxy–substituted carbenes with alkenes

“…Hoffmann predicted that a C 2v cyclic four-electron transition state in which both C-C bonds form simultaneously is orbital-symmetry forbidden; 1,2 therefore, non-least motion approach was proposed by Hoffmann 2 and Moore 3 in which there is initial interaction of the electrophilic empty p-orbital (LUMO) of the carbene with the nucleophilic filled π-orbital (HOMO) of the alkene. 1 This prediction was subsequently verified many times with semiempirical [4][5][6] and ab initio methods 7,8 and was shown to be influenced by a second pair of orbital interactions between the lone pair (HOMO) of the carbene with the π* antibonding orbital (LUMO) of the alkene, which becomes dominant for electron-donor substituted carbenes. 8 Carbene cycloadditions have been extensively studied experimentally and computationally by the groups of Moss and Krogh-Jespersen over the last decade.…”

“…1 This prediction was subsequently verified many times with semiempirical [4][5][6] and ab initio methods 7,8 and was shown to be influenced by a second pair of orbital interactions between the lone pair (HOMO) of the carbene with the π* antibonding orbital (LUMO) of the alkene, which becomes dominant for electron-donor substituted carbenes. 8 Carbene cycloadditions have been extensively studied experimentally and computationally by the groups of Moss and Krogh-Jespersen over the last decade. [9][10][11][12] They combined laser flash photolysis and density functional theory calculations to determine activation parameters for a series of carbene cycloadditions.…”