P562: Insights into hypervalency from general valence bond theory: The recoupled pair bond model

Author: Lu T. Xu, University of Illinois at Urbana-Champaign, USA

Co-Author: Tyler Y. Takeshita and David E. Woon, University of Illinois at Urbana-Champaign, USA; Thom H. Dunning Jr., University of Illinois at Urbana-Champaign, Northwest Institute for Advanced Computing, Pacific Northwest National Laboratory, University of Washington, Seattle, USA

Date: 8/5/14

Time: 4:00 PM4:20 PM

Room: MAN 123

Related Symposium: S36

Generalized Valence Bond (GVB) theory provides a compelling description of the electronic structure of molecules. The GVB wave function is more accurate and intuitive than the Hartree-Fock (or molecular orbital) wave function presenting a simple, yet accurate chemical interpretation of the bonding in complex molecules. The GVB wave function provides a natural description of the bonding in a class of molecules that has long confounded chemists-hypervalent molecules such as PCl5, SF4 and ClF3 in which the valence of the central atom exceeds the nominal valence of that element. We have found that these molecules possess a new type of bond, the recoupled pair bond dyad (and its predecessor, the recoupled pair bond). We will show how the recoupled pair bond model provides a simple and appealing description of the bonding in hypervalent molecules. The concepts to be presented are actively applied in modern-day research, yet are appropriate for the general chemistry curriculum. The potential impact of implementing these ideas in the current curriculum will also be discussed.

P563: Vertex or edge inversion? Understanding NH3, NF3, PH3 and PF3 inversion with recoupled pair bonding model

Author: Lu T. Xu, University of Illinois at Urbana-Champaign, USA

Co-Author: Tyler Y. Takeshita, University of Illinois at Urbana-Champaign, USA; Thom H. Dunning Jr., University of Illinois at Urbana-Champaign, Northwest Institute for Advanced Computing, Pacific Northwest National Laboratory, University of Washington, Seattle, USA

Date: 8/5/14

Time: 4:20 PM4:40 PM

Room: MAN 123

Related Symposium: S36

Pyramidal molecules such as NH3, PH3 and NF3 invert through a planar D3h transition state. This process is also known as vertex inversion. However, PF3 inverts through a T-shaped transition state and this type of inversion pathway is called edge inversion. The recoupled pair bonding model, derived from Generalized Valence Bond theory, provides an intuitive way of understanding and teaching the differences between these two types of inversion process. The different preference of forming an s-recoupled pair bond dyad (D3h) or p-recoupled pair bond dyad (T-shaped) in the transition state molecules is the underlying reason for the change in the structure of the transition state in this series. With orbital diagrams, the bonding nature of both the ground state and inversion transition state of NH3, PH3, NF3 and PF3 can be rationalized and taught easily within the general framework of recoupled pair bonding model.

P446: Nature of atomic lone pairs: A first step to understanding hypervalency

Author: Tyler Y. Takeshita, University of Illinois at Urbana-Champaign, USA

Co-Author: David E. Woon, University of Illinois at Urbana-Champaign, USA; Thom H. Dunning Jr., University of Illinois at Urbana-Champaign, Northwest Institute for Advanced Computing, Pacific Northwest National Laboratory, University of Washington, USA

Date: 8/5/14

Time: 11:30 AM11:50 AM

Room: MAN 123

Related Symposium: S36

Atoms are the essential building block of molecules. Unfortunately, existing bonding models are unable to describe why some atoms are capable of exceeding their nominal valence to form hypervalent molecules, while others are not. To understand such puzzling behavior we must first understand an atom’s capacity to utilize the electrons occupying its lone pair orbitals and how they differ from that of other elements. For example, both carbon and sulfur must use the electrons in their lone pair 2s2 and 3p2 orbitals in order to form CH4 and SF4, yet the electrons in oxygen’s lone pair 2p2 orbitals are, in general, inaccessible. Why is this so? This presentation introduces Generalized Valence Bond (GVB) theory and demonstrates that variations in the accessibility of the electrons in an atom’s lone pair orbitals are clear and intuitive within this framework. The concepts to be presented are actively applied in modern-day research, yet appropriate for the general chemistry curriculum. The potential impact of implementing these ideas in the current curriculum will also be discussed.

P447: Insights into chemical bonding from general valence bond theory

Author: Tyler Y. Takeshita, University of Illinois at Urbana-Champaign, USA

Co-Author: Lu T. Xu and David E. Woon, University of Illinois at Urbana Champaign, USA; Thom H. Dunning Jr., University of Illinois at Urbana-Champaign, Northwest Institute for Advanced Computing, Pacific Northwest National Laboratory, University of Washington Seattle, USA

Date: 8/5/14

Time: 11:50 AM12:10 PM

Room: MAN 123

Related Symposium: S36

Generalized Valence Bond (GVB) theory provides a compelling description of the electronic structure of molecules. The GVB wave function is more accurate than the traditional molecular orbital (MO) wave function and accurately describes bond formation, an essential molecular process that traditional MO wave functions cannot properly model. Further, the atomic parentage of the GVB orbitals in the molecule can be easily identified, which enables the electronic structure of the molecule to be connected with that of the atoms of which it is composed. We will discuss a number of examples of the GVB theory of chemical bonds, ranging from covalent to polar covalent to ionic bonds, which illustrate the power of the GVB approach. Special emphasis will be placed on the potential for GVB theory to modernize the general chemistry curriculum and better prepare students for advanced course material.