7.01 | Symmetry of SALCS & Stability of Allene

June 16, 2024 | In the first of the in-classes exercises, we studied the symmetry adapted linear combinations of anthracene. The fourteen Pz orbitals give rise to fourteen different symmetry adapted linear combinations. The task at hand was to determine the symmetry of these fourteen different SALCS. We demonstrated that by using the character table and analyzing how the SALCs “behave” under certain symmetry operations, we could readily figure out what the symmetry of the corresponding SALCS was. In the second question we examined and constructed, via the method of inspection, the MO-diagram of allene in two different confirmations. By using the combination of two CH2 fragments with a central carbon atom, and by cleverly using different symmetry operations we could distinguish the different orbitals with respect to a mirror plane. With the symmetry (symmetric or asymmetric) established, the MO-diagram is readily constructed and the stability of allene with different electron counts could be evaluated. The exercises and answer key are attached in the additional materials with this lecture.

The link to the video can be found below