7.02 | The MO Diagram of Boron Trifluoride | π-contributions from the SALCS

Sunday June 23rd, 2024 | In this problem solving session, we take a look at the MO-diagram of boron trifluoride. The only exception with previous problem sets is that this time we also take into account the Px, Py, and Pz orbitals on fluorine that are able to engage in additional σ- and π-interaction with the boron atom. As usual, the symmetry of the orbitals on boron could be obtained directly from the character table. However, for fluorine the symmetry adapted linear combinations needed to be established (SALCS). Since in this exercise we are considering more than σ-only interactions (i.e., the Pz and Py are used), we also have to establish a separate coordinate systems on the fluorine atoms, making sure behave identically under the listed symmetry operations of the point group (D3H). By doing so we found that the SALCS of the corresponding p-orbitals could be found by assigning “+” and “-” to the p-orbitals (depending on their sign) and making sure the assignment is repeated in the SALCs. In this way, the SALCS of π-symmetric orbitals could be found and accurately represented. Finally in this example we also realized for the first time that although sometimes orbitals have the same symmetry and energy, interactions are still prohibited because of their relative orientation towards another (e.g., they happen to be in each others nodal planes). The question and answer key are located in the additional materials with this lecture.

The link to the video can be found below: