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    • Keywords

       

      3(4'-substituted)phenylfuroxans; ranges of electron-releasing and electron-attracting substituents; substituent-dependent N-oxide bond lengths from B3LYP/6-311++G; inverse residual charge changes at N-2 and O-6; N-oxide bond dissociation and second-order perturbation energies from B3LYP/6- 31++G and BLYP/6-31++G; back donation from O to N in N

    • Abstract

       

      The N-oxide nitrogen in C-4 substituted 3-phenyl furoxans occupies a position analogous to C-β in 4-substituted styrenes that have been examined for modes of transmission of substituent effects from theC-4 substituent to C-β. From geometry optimizations through high-level MO theory calculations, it was firstensured that the N-2–C-3 liaison in 3-(4-substituted)phenyl furoxans retains as much double-bond characteras it does in the case of furoxan bearing no substituents and that the para-substituted phenyl and furoxan ringsmaintain near uniplanarity. The calculations, carried out for such furoxans, chosen to represent a spectrum ofeffects from electron-donor to electron-acceptor, showed how the change in the 4-substituent affects electronredistribution within N-oxide group in the way expected: while the residual positive charge at N increases theresidual negative charge at O decreases. An increase in the N-oxide bond order (as measured by the Wibergbond index), together with a small reduction in the N-2–O-6 bond length, was also found. That these effectswere not artefacts of the calculation procedure was ensured when the calculations, repeated using a differentfunctional, showed not only inverse dependence of positive N-2 and negative O-6 net charges on N-2–O-6bond lengths but also confirmatory evidence from N-oxide bond dissociation and second-order perturbationenergies. These results are interpreted as demonstrating graded back donation from O to N within the N → O group caused by a combined action of mesomerism and ᴨ-polarisation involving the substituent at the parapositionof the phenyl group offering a spectrum of effects from electron-releasing to electron-withdrawing.

    • Graphical Abstract

       

      Calculations at the B3LYP/6-31++G** level have shown that back donation from O to N in N → O in 3-(4-X-phenyl) furoxans increase with a change of X from electron-donor to electron-acceptor.

    • Author Affiliations

       

      S NATARAJAN BALASUBRAHMANYAM1 BISHWAJIT GANGULY2 RABINDRANATH LO3 BALAKRISHNA RAJAN MUSIRI M4 MOORKKANNUR N SREERAG4 SHARAFUDEEN P C4 OSHIYA R A4 NACHIAPPAN RAJENDRAN5

      1. Formerly of the Department of Organic Chemistry, Indian Institute of Science, Bangalore, Karnataka, India
      2. Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat, India
      3. Institute of Organic Chemistry and Biochemistry, Prague, Czech Republic
      4. Chemical Information Sciences Laboratory, Department of Chemistry, Pondicherry University, Puducherry, India
      5. GTN Arts College, Dindigul, Tamil Nadu, India
    • Dates

       
  • Journal of Chemical Sciences | News

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