An example of a Lewis acid is BH 3, and an example for a Lewis base is NH 3. What happens in a Lewis-acid base reaction? The Lewis base donates an electron pair to form a covalent bond with the Lewis acid (Fig. 4.1.2).

SOMO, HOMO, and LUMO Previous examples of “pathological” bonding and the BH3 molecule illustrate how a chemist’s use of localized bonds, vacant atomic orbitals, and unshared pairs to understand molecules compares with views based on the molecule’s actual total electron density, and with computational molecular orbitals.

This lecture then focuses on understanding reactivity in terms of the overlap of singly-occupied molecular orbitals (SOMOs) and, more commonly, of an unusually high-energy highest occupied molecular orbital (HOMO) with an unusually low-energy …

-In addition, B has 3 electrons in the valence electrons and 3 hydrogens have total 3 electrons. Therefore, the total number of electrons filled in orbitals are 6. With all of the informations above about symmetry labels of B atom and the 3 LGOs, we now construct the MO diagram of BH3.

For the following reactions, show (i) the HOMO-LUMO interaction and (ii) the molecular orbital interaction diagram for formation of the new molecule. A fluoride ion donates to a boron trifluoride molecule (BF 3 ), forming a tetrafluoroborate ion (BF 4 - ).

The low LUMOs that make both HF and CH3F acidic are analyzed and compared underlining the distinction between MO nodes that derive from atomic orbitals nodes (AON) and those that are antibonding (ABN). Reaction of HF as an acid with OH- is shown to involve simultaneous bond-making and bond-breaking. Why So High, Why So Low?

• What can the HOMO and LUMO tell us about the chemical nature of BH3? o the highest occupied molecular orbital or HOMO of BH 3 is a degenerate e' MO while the lowest unoccupied molecular orbital or LUMO is a non-bonding p z orbital (a2" symmetry) on the B atom. The a2" orbital is low in energy because boron is an electropositive

Jun 9, 2010 · This lecture then focuses on understanding reactivity in terms of the overlap of singly-occupied molecular orbitals (SOMOs) and, more commonly, of an unusually high-energy highest occupied molecular orbital (HOMO) with an unusually low-energy lowest unoccupied molecular orbital (LUMO).

The HOMO/LUMO view of chemical reactivity requires recognizing whether a particular HOMO should be unusually high in energy (basic), or a particular LUMO should be unusually low (acidic). The approach is illustrated with BH3, which is both acidic and basic and thus dimerizes by forming unusual “Y” bonds.

What can the HOMO and LUMO tell us about the chemical nature of BH3? the HOMO of BH3 is a degenerate e' MO while the LUMO is a non-bonding pz orbital (a2" symmetry) on the B atom.