• Partitioning of methyl internal rotational barrier energy of thioacetaldehyde

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    • Keywords

       

      Methyl rotation; natural bond orbitals; Pauling exchange interaction; thioacetaldehyde

    • Abstract

       

      The nature of methyl internal rotational barrier in thioacetaldehyde has been investigated by relaxation effect, natural bond orbital (NBO) analysis and Pauling exchange interactions. The true experimental barrier can be obtained by considering fully relaxed rotation. Nuclear-electron attraction term is a barrier forming term in the fully relaxed rotation, but it appears as an antibarrier for rigid rotation. It is seen that during methyl rotation, the torsional mode is coupled with the aldehydic hydrogen out-of-plane wagging motion. Natural bond orbital analysis shows that the principal barrier forming term originates from the C-C bond. The lengthening of the C-C bond is explained by considering charge transfer interaction between several bonding and antibonding orbitals in the C-C bond region, which leads to higher bonding overlap for the eclipsed conformer compared to the staggered conformer. S-C(σ)/Cme-Hp and C-Hald/Cme-Hop interactions appear to be the main barrier-forming Pauling exchange terms but have less contribution to make to the barrier compared to the C-C bond interaction.

    • Author Affiliations

       

      Nikhil Guchhait1

      1. Department of Chemistry, Indian Institute of Technology, North Guwahati, Guwahati - 781 039, India
    • Dates

       
  • Journal of Chemical Sciences | News

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