Lecture #18
 
  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.
Lecture Outline Review for Exam II
List of topics for EXAM II.
What's expected for geometrical isomers for these two?
 
There is more than one geometrical isomer that can be constructed at first.
 
We will use VSEPR to determine bond angles in a collection of different illustrations some of which are shown here.

In the first, all angles are 120o since the benzene ring, because of resonance, is a perfect hexagon with 120o internal angles.

The second, after focussing attention on the N as a central atom has its lone pair compressing the other single bonds closer than their ideal 109.5o (despite having drawn the lone pair as if it were inside the ring -- which it isn't)
Examples
 
Careful!
 
Practice in finding structural isomers and finishing Lewis structure pictures.
 
 
Expanded octet needed.
 
Examples
 
Examples
 
Molecular basis of acid strength. The comparison is with selenic acid which is OSe(OH)3. This is a tougher level question for review purposes.