Sigmatropic hydrogen shifts in aryltetraphenylcyclopentadienes |
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Authors: | G A Dushenko I E Mikhailov O I Mikhailova R M Minyaev V I Minkin |
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Institution: | 1.Southern Scientific Center,Russian Academy of Sciences,Rostov-on-Don,Russia;2.Research Institute of Physical and Organic Chemistry,Southern Federal University,Rostov-on-Don,Russia |
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Abstract: | Dynamic NMR has revealed intramolecular migrations of hydrogen atom over the periphery of the five-membered ring in 5-(p-tolyl)-1,2,3,4-tetraphenylcyclopentadiene in a deuteronitrobenzene solution with energy barrier ΔG 180 ≠ = 24.8 kcal/mol. Quantum-chemical DFT calculations B3LYP/6-311++G** have shown that such migrations in 1,2,3,4,5-pentaphenylcyclopentadiene in the gas phase occur in a chiral conformation of propeller type by the mechanism of 1,5-sigmatropic hydrogen shifts with retention of configuration through asymmetric transition state with energy barrier ΔE ZPE ≠ = 25.9 kcal/mol. Enantiomers P and M can readily interconvert into each other (ΔE ZPE ≠ = 3.9 kcal/mol) owing to synchronous flip rotations of the phenyl groups. |
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