Question

4. Consider the following AHz molecule where A is an element like carbon. This molecule could be either trigonal planar (D3h), or could distort so that one A-H bond is longer than the other two with the molecule then becoming C2v: Construct a Walsh diagram showing the changes in bonding between the two geometric situations, and predict whether LiH3t will be C2v or D3h.

Answer 1

Walsh diagrams help in the representation and comparison between the energies of different conformations of a molecule with the change in the bond angle. It also helps in predicting the point group symmetry of different molecules.

However, the change in angle of AH₃ type molecule from 120^° to 90^° changes the point group from D_3h to C_3v respectively, but in this case of LiH₃^{+ ,} it has only 3 valence electrons, and these can easily be filled in the lower sigma energy orbitals(bonding molecular orbitals) which makes it planar in its ground state. Therefore, the point group symmetry for this molecule will be C_2v

WALSH DIAGRAM FOR AH MOLECULE ANTIBONDING MOLECULAR ORBITAL ANTIBONDING MOLECULAR OR BITAL Bond enugч NON-BONDING MOLECULAR ORBITAL NON-BONDA MOLECUIA ORGITAL 9,SA BonDin MOLECULAR 40 1200 DRBITAL BOND ANGE и И И h PuRAMIDAL TRI4DNAL PLANAR