Molecular orbital analysis of the reaction paths for termolecular reactions

Abstract

<span style="font-size:12.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-in;mso-fareast-language:en-in;mso-bidi-language:ar-sa"="" lang="EN-IN">The possibility of a six centered transition state for the termolecular exchange reaction between three diatomic molecules <span style="mso-bidi-font-style:italic">(A₂ + B₂+ C₂ →7 AB + BC + CA) is investigated using Extended Huckel Theory. Our present calculations show that a concerted six-centered reaction mechanism is energetically more favourable compared to the atomic mechanism for these type of reactions. An analysis of the molecular orbitals of the transition state shows that the six <span style="font-size:12.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-in;mso-fareast-language:en-in;mso-bidi-language:ar-sa"="" lang="EN-IN"><span style="mso-bidi-font-style:italic"><span style="font-size:12.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-in;mso-fareast-language:en-in;mso-bidi-language:ar-sa"="" lang="EN-IN">σ electrons, originating from the each atom, are completely delocalized throughout the cyclic, six-membered transition state. This effect is analogous to the delocalization observed in conjugated cyclic systems containing (4n+2) π electrons. The concept of sigma aromaticity arising from the deloealization of sigma electrons in cyclic transition states can be successfully applied to explain the mechanism of termolecular reactions.</span></span></span></span></span>