Lecture #36
Review for Exam IV
  CURMUDGEON GENERAL'S WARNING. These "slides" represent highlights from lecture and are neither complete nor meant to replace lecture. It is advised not to use these as a reliable means to replace missed lecture material. Do so at risk to healthy academic performance in 09-105.
These next few slides were not gone over in class, but become an optional discussion of bonding in transition metal ion complexes as covered in Section 19.7 in the text. It uses pure atomic orbitals instead of hybrid atomic orbitals, but the concepts of atomic orbital overlap giving rise to bonding, antibonding, and non-bonding combinations is as we have seen before. The figure is what we will attempt to explain, starting closer to the beginning of its construction for an octahedral geometry. It contrasts in its starting point with our use of hybrid orbitals on the transition metal ion.
Atomic orbitals on the metal beyond the closed shell inner core. Recall that the ion doesn't put its electrons in any s-valence orbital, but uses d-orbitals instead.
For ligand orbitals in donor atoms on the x, y, and z axes, some will overlap properly with the d-orbitals on the transition metal.
Some will not.
An example where we get a non-bonding orbital between the donor and the central species.
The molecular orbital energy correlation diagram showing the resulting bonding, anti-bonding, and non-bonding combinations. The valence electron pairs are from each of the six donor atoms in the octahedral complex. Just above the sigma bonding orbitals are where the next electrons would go, provided by the transition metal ion. These are our old friends the t2g and egbut under different names.
A practice problem
Three isomers. No optical isomers, all geometric.
And another
Rotate the right figure around the verticle axis by 180o and the same molecule results. No isomer.
..on and on we go....(assuming that we have a regular trigonal prism with equilateral sides)
Rank the following six chlorobenzenes in order of expected increasing boiling points.
The relative polarities of the different sets were actually done in lecture awhile ago. Here are the polarities and the boiling points.
If each asymmetric carbon gives you two isomers (enantiomers/chiral isomers), then two such carbons in the same molecule gives you four possible isomers. How many isomers of taxol are possible?

There will be twelve 'stereocenters' giving 212 or more than four thousand possible combinations.

Self-explanatory. (Non-polar, no hydrogen bonding...size!)