Construct a qualitative MO diagram for the following systems and discuss how the πMOs are modifi

Construct a qualitative MO diagram for the following systems...

Key Concepts

Orbital Symmetry and Overlap

Effective mixing of orbitals to form molecular orbitals relies on having compatible symmetry and good overlap. When substituents are introduced, the symmetry of the system may change, altering which atomic or fragment orbitals can combine, leading to shifts in the energies and characters of the resulting molecular orbitals.

Electronegativity and Orbital Energy

Substituents with differing electronegativities will influence the energies of the molecular orbitals. Electron-withdrawing groups can stabilize (lower the energy of) the neighboring orbitals, while electron-donating groups can destabilize (raise the energy of) them, thereby affecting the reactivity and spectral properties of the molecule.

Conjugation and Delocalization

Conjugation refers to the alternation of double and single bonds which allows for delocalization of electrons across several adjacent atoms. This delocalization stabilizes the molecule and modifies its electronic structure, contributing to changes in the optical and chemical properties as observed in extended ? systems.

? Molecular Orbitals

? molecular orbitals arise from the lateral overlap of p orbitals and are characteristic of multiple bonds and conjugated systems. These orbitals are crucial for understanding electron delocalization and the electronic properties of unsaturated molecules and aromatic systems.

Qualitative Molecular Orbital Diagrams

Qualitative MO diagrams are schematic representations that display the relative energies and interactions of atomic and group orbitals in a molecule. They help in predicting bonding, nonbonding, and antibonding interactions without requiring complex calculations, allowing for insights into molecular stability, reactivity, and electronic transitions.

Substituent Effects on ? Systems

The introduction of a substituent alters the ? molecular orbital system by contributing additional orbital interactions. Depending on whether the substituent is electron-donating or electron-withdrawing, it can raise or lower the energy levels of the ? MOs, modify the distribution of electron density, and affect the overall conjugation in the molecule.

Transcript

00:01 1 .35 hextriene has six molecular orbitals shown here labeled 1 through 6, psi 1 through psi 6.

00:10 And each p orbital in these molecular orbitals are slightly different sizes, but that's just because of the image i have.

00:19 But you can think of them all as the same size, even though in reality each one will contribute slightly differently to the slightly different amounts to the molecular orbital as shown here.

00:29 But because we have six p orbitals in each of the six carbons, we'll get six molecular orbitals.

00:35 And these bottom three that are lower in energy are occupied by the six electrons.

00:41 So the question asks us to find the bonding and anti -bonding molecular orbitals.

00:46 And to do that, we need to consider the bonding and anti -bonding interactions in each molecular orbital.

00:54 So down here in sie 1, this is a bonding orbital.

00:59 And it's bonding because all of these interactions are bonding.

01:03 All of the p -orbital are in the same phase, and we can have overlap between each of these, because they're all in the same phase.

01:14 So this is a bonding.

01:16 Sci2 is also a bonding because we have the same phase here and here and here and here, and here, and we only have one anti -bonding interaction right here.

01:29 And that's one node as well, but we'll get to that in another.

01:33 Part of the question.

01:35 We have bonding interaction here and here and here and here.

01:41 And then we have two anti -bonding interactions here and here, but we still have more bonding than antibonding, three bonding, two anti -bonding.

01:47 So this is also a bonding.

01:50 M .o.

01:52 Oops.

01:54 This is also bonding.

01:56 And these three appear anti -bonding because they have more anti -bonding interactions than bonding interactions.

02:06 Anti -bonding.

02:09 And notice how these are unoccupied.

02:11 And i'll just do sifor and then we can move on to the next part.

02:14 Well, i'll end up doing them all actually.

02:16 Why not? okay, so this has here we have a change in phase between this tup orbital.

02:21 So that's a node.

02:22 We have bonding interactions here.