Stereoelectronic effects in Menshutkin‐type SN2 reactions: theoretical study based on through‐space/bond orbital interaction analysis. (5th August 2013)

• Record Type: Journal Article
• Authors: Jiang, Lizhi; Orimoto, Yuuichi; Aoki, Yuriko
• Is Part Of: Journal of physical organic chemistry. Volume 26:Number 11(2013:Nov.)
• Page Start: 885
• Page End: 891
• Publication Date: 2013-08-05
• Subjects: activation energy -- electron transfer -- Menshutkin reaction -- orbital interaction -- SN2 reaction -- substituent effect -- transition state; Chemistry, Physical organic -- Periodicals; 547.1
• DOI: 10.1002/poc.3186
• Languages: English
• ISSNs: 0894-3230

Abstract

Abstract : Through‐space/bond orbital interaction analysis has been applied to investigate the stereoelectronic effects on stabilizing the transition state of Menshutkin‐type SN 2 reactions. The mechanism of how the substituent effects work on accelerating the reactions has been demonstrated from orbital interaction perspective. The geometrical structures and Mulliken charge distributions have been compared to elucidate the substituent effects for the SN 2 reaction center. It is found that the substituents lower the activation energies by strengthening the orbital interactions in the SN 2 reaction process. When electron‐donating and electron‐accepting substituents (–C6 H5 and –CHO) are introduced to the same central carbon at the reaction center, the symmetry allows the π–π* interactions among the donor and acceptor in the transition state. It stabilizes the transition state much more than the reactant complex. And the π–π* interactions are estimated to decrease about 2.28 kcal/mol of the energy for transition state. The σ‐like orbitals of the partial bond around the central carbon are reactive, and the σ–π* orbital interactions stabilize the reactant complex much more than the π–σ* interaction. When the σ–π* and π–σ* interactions are deleted from the system, the activation energy increases and turns close to the values of the systems which are without such substituents. It can be concluded that the π–π*, σ–π*, and π–σ* interactions cooperatively accelerates the SN 2 reaction by stabilizing its transition state. Copyright © 2013 John Wiley & Sons, Ltd. Abstract : Through‐space/bond orbital interaction analysis was applied to investigate the stereoelectronic effect on stabilizing the transition state of SN 2 reactions. Substituents (–C6 H5 and –CHO groups) lower the activation energies by strengthening the orbital interactions of transition states. The activation energy increases close to the value of the system, which is without such substituents, when the orbital interactions are deleted.