Theoretical and experimental studies on the structure and isomerization of isocyano and cyano cyclopolyenes |
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Authors: | O I Mikhailova G A Dushenko I E Mikhailov R M Minyaev V I Minkin |
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Institution: | (1) Institute of Physical and Organic Chemistry, Southern Federal University, pr. Stachki 194/2, Rostov-on-Don, 344090, Russia;(2) Southern Research Center, Russian Academy of Sciences, ul. Chekhova 41, Rostov-on-Don, 344006, Russia |
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Abstract: | Quantum-chemical calculations in terms of the density functional theory showed that cyclopolyenyl isocyanides RNC are considerably less stable than the corresponding cyanides and that they are capable of undergoing RNC → RCN isomerization according to both 1,2-shift mechanism (cyclopropenyl and cyclopentadienyl isocyanides; ΔE ≠ = 35.0 and 37.5 kcal/mol, respectively) and previously unknown 2,5-sigmatropic shift mechanism (cycloheptatrienyl isocyanide, ΔE ≠ = 26.4 kcal/mol). Migration of cyano group in the cyclopentadiene and cycloheptatriene systems follows the 1,5-sigmatropic shift pattern. The activation barrier to 1,5-shift of cyano group around the cycloheptatriene ring was estimated by dynamic NMR in deuterated nitrobenzene (ΔG 190°C ≠ = 26.5 kcal/mol). |
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