Reversible Migrations of Nitro Group in a Methyltetramethoxycarbonylcyclopentadiene System |
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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.Institute of Physical and Organic Chemistry,Southern Federal University,Rostov-on-Don,Russia;2.Southern Scientific Center,Russian Academy of Sciences,Rostov-on-Don,Russia |
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Abstract: | Quantum chemical calculations by the density functional theory method at the B3LYP/6-311++G** level have shown that 5-nitro-5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene (1) and 5-nitro-2-methyl- 1,3,4,5-tetramethoxycarbonylcyclopentadiene (2) undergo interconversion by consecutive 1,5-sigmatropic shifts via the formation of an unstable isomer, 5-nitro-1-methyl-2,3,4,5- tetramethoxycarbonylcyclopentadiene (3), rather than through the NMR-detected 1,3-shift of the nitro group over the cyclopentadiene ring perimeter. According to calculations in the gas phase, isomer 3 is by ΔE ZPE of 3.6 kcal/mol less stable than isomer 1, while the activation barrier of the stepwise 1 → 2 process is 24.5 kcal/mol, which agrees well with NMR data (ΔG25C≠, chlorobenzene, 26.5 kcal/mol). |
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