Acetylene-vinylidene isomerization

Zou, S.L. Bowman, J.M. A new ab initio potential energy surface describing acetylene/vinylidene isomerization. Chem. Phys. Lett. 2003, 368, 421-424. 

Chen, Y.Q. Jonas, D.M. Kinsey, J.L. Field, R.W. High-resolution spectroscopic detection of acetylene-vinylidene isomerization by spectral crosscorrelation. J. Chem. Phys. 1989, 91, 3976-3985. 

Field, R.W. Jacobson, M.P. Order out of chaos Local bends above the energy of the acetylene-vinylidene isomerization barrier. In Abstracts of papers of the American Chemical Society 217, 141-PHYS Part 2, Mar 21, 1999. 

Chen, Y. Pique, J.P. Field, R. Kinsey, J.L. A spectroscopic study of acetylene-vinylidene isomerization. In Abstracts of papers of the American Chemical Society 193, 117-PHYS, Apr 5, 1987. 

Fig. 11 (A) Acetylene—vinylidene isomerization. (B) Metal-induced acetylene to vinyli-dene tautomerization.

DFT calculations confirmed the similarities with the alkyne/vinylidene transformation but have revealed that additional parameters were essential to achieve the isomerization [8, 20-23]. The hydride ligand on the 14-electron fragment RuHC1L2 opens up a pathway for the transformation similar to that obtained for the acetylene to vinylidene isomerization. However, thermodynamics is not in favor of the carbene isomer for unsubstituted olefins and the tautomerization is observed only when a re electron donor group is present on the alkene. Finally the nature of the X ligand on the RuHXL2+q (X = Cl, q=0 X = CO, q=l) 14-electron complex alters the relative energy of the various intermediates and enables to stop the reaction on route to carbene. 

For a vibrationally highly excited acetylene, the isomerization process from acetylene to vinylidene is of interest (see Fig. 3.20). In this process, both of the bending modes and should be excited where one of the hydrogen atoms goes half-way round the two carbon atoms. Therefore, the reaction coordinate of the isomerization is chosen to be the sum -H v. However,... 

Another mode of activation of o-alkynylanilines 105, involving an alkyne-vinyl-idene isomerization, was reported by Mc-Donald (Scheme 9.40) [191]. High yields of 1-monosubstituted indoles 106 were obtained upon cydoisomerization of terminal o-alkynylanUines 105 using an in situ generated Et3N Mo(CO)5 catalyst. The authors proposed a mechanism involving the initial alkyne-vinylidene isomerization [192-194] of a terminal acetylene 105 into the reactive carbenoid 107. The... 

The reaction between acetylene and RhfCOXi CjH i -QH,) [which acts as a source of the Rh(COXf/5-C9H7) fragment] affords 33 in 50% yield (61). The reaction is supposed to proceed via oxidative addition of the alkyne to the rhodium fragment, followed by isomerization to the vinylidene complex which then interacts with a second rhodium fragment ... 

Schork, D. Koppel, H. Barrier recrossing in the vinylidene-acetylene isomerization reaction A five-dimensional ab initio quantum dynamical investigation. J. Chem. Phys. 2001, 115, 7907-9723. 

Conrad, M.P. Schaefer, H.F., III. Absence of an energetically viable pathway for triplet 1,2 hydrogen shifts. A theoretical study of the vinylidene-acetylene isomerization. J. Am. Chem. Soc. 1978, 100, 7820-7823. 

The acetylene anion radical undergoes autodetachment of the electron, but the vinylidene anion can be generated easily [83]. Since the calculated isomerization barrier is -45 kcal/mol, the 2B2 ground-state vinylidene anion radical is predicted to be stable with respect to the 1,2-hydrogen shift [30, 84, 85]. As mentioned before, the vinylidene anion radical was used as the precursor for the generation of the singlet vinylidene in Lineberger s experimental studies. 

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