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<p>The effect of mono- and di-substitution of the terminal –C ≡ CH groups of <i>cis</i>-1,2<b>-</b>diethynylcyclopropane with CH/N or CH/P moieties has been theoretically investigated at the DFT (B3LYP/6–31 +G(d)) level. On substitution of one or both CH groups with phosphorus atoms, there is remarkable decrease in the activation free energy barriers (ΔG<sup>#</sup>) for both reaction steps and the overall process becomes exergonic. In contrast, on similar substitution with the nitrogen atom, there is distinct increase in the ΔG<sup>#</sup> values and both reactions turn endergonic. These opposing trends could be rationalized on the basis of the relative strengths of the C≡ P and C ≡ N bonds, the former being significantly weaker than the latter. The effect of replacing CH₂ group in the cyclopropane ring with heteroatoms (NH or PH) was also investigated at the same theoretical level, when broadly similar trends were observed.</p>

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A DFT modeling of the effect of CH/N and CH/P exchanges on tandem Cope rearrangement and [2+2] cycloaddition of cis-1,2-diethylnylcyclopropane and its mono-hetero analogues

  • 期刊论文

  • 发表日期：

    2025年11月26日

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  • Ayushi Shekhawat,
  • Raj K. Bansal

摘要

The effect of mono- and di-substitution of the terminal –C ≡ CH groups of cis-1,2-diethynylcyclopropane with CH/N or CH/P moieties has been theoretically investigated at the DFT (B3LYP/6–31 +G(d)) level. On substitution of one or both CH groups with phosphorus atoms, there is remarkable decrease in the activation free energy barriers (ΔG#) for both reaction steps and the overall process becomes exergonic. In contrast, on similar substitution with the nitrogen atom, there is distinct increase in the ΔG# values and both reactions turn endergonic. These opposing trends could be rationalized on the basis of the relative strengths of the C≡ P and C ≡ N bonds, the former being significantly weaker than the latter. The effect of replacing CH₂ group in the cyclopropane ring with heteroatoms (NH or PH) was also investigated at the same theoretical level, when broadly similar trends were observed.