Frontside versus Backside SN2 Substitution at Group 14 Atoms: Origin of Reaction Barriers and Reasons for Their Absence
- 29 September 2008
- journal article
- research article
- Published by Wiley in Chemistry – An Asian Journal
- Vol. 3 (10), 1783-1792
- https://doi.org/10.1002/asia.200800065
Abstract
We have theoretically studied the gas‐phase nucleophilic substitution at group‐14 atoms (SN2@A) in the model reactions of Cl−+AH3Cl (A=C, Si, Ge, Sn, and Pb) using relativistic density functional theory (DFT) at ZORA‐OLYP/TZ2P. Firstly, we wish to explore and understand how the reaction coordinate ζ, and potential energy surfaces (PES) along ζ, vary as the center of nucleophilic attack changes from carbon to the heavier group‐14 atoms. Secondly, a comparison between the more common backside reaction (SN2‐b) and the frontside pathway (SN2‐f) is performed. The SN2‐b reaction is found to have a central barrier for A=C, but none for the other group‐14 atoms, A=Si–Pb. Relativistic effects destabilize reactant complexes and transition species by up to 10 kcal mol−1 (for SN2‐f@Pb), but they do not change relative heights of barriers. We also address the nature of the transformation in the frontside SN2‐f reactions in terms of turnstile rotation versus Berry‐pseudorotation mechanism.Keywords
This publication has 82 references indexed in Scilit:
- Transition‐State Energy and Position along the Reaction Coordinate in an Extended Activation Strain ModelChemphyschem, 2007
- Activation of H−H, C−H, C−C and C−Cl Bonds by Pd and PdCl-. Understanding Anion Assistance in C−X Bond ActivationJournal of Chemical Theory and Computation, 2005
- Ion Pair SN2 Reactions. Theoretical Study of Inversion and Retention MechanismsJournal of the American Chemical Society, 1995
- Central bond in the three CN.cntdot.dimers NC-CN, CN-CN and CN-NC: electron pair bonding and Pauli repulsion effectsThe Journal of Physical Chemistry, 1992
- Gas-phase ion/molecule reactions as studied by Fourier transform ion cyclotron resonanceAccounts of Chemical Research, 1990
- The application of density functional theory to the optimization of transition state structures. I. Organic migration reactionsThe Journal of Chemical Physics, 1990
- The stereochemistry of nucleophilic substitution of tetracoordinate siliconChemical Reviews, 1990
- Gas-phase reactions of anions with substituted silanesJournal of the American Chemical Society, 1980
- Non‐rigid Molecular Skeletons—Berry Pseudorotation and Turnstile RotationAngewandte Chemie, 1971
- Role of pseudorotation in the stereochemistry of nucleophilic displacement reactionsAccounts of Chemical Research, 1970