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
We will use VSEPR to determine bond angles in a collection of different illustrations some of which are shown here.
Several lectures ago, we asked about the remaining structural isomers of C4H8. The skeletal structures are shown. One is four carbons in a row. (It doesn't matter whether this is drawn straight, crooked, or even L-shaped.) The other frame is branched.  
The text gives a recipe for figuring out Lewis structures. However, it is only useful if you know where the atoms are. Furthermore, it does not take into account the possibility of expanded octets (which, however, are not relevant to this example). We follow the recipe to note that a double bond must be present. That allows us to place the hydrogens correctly.  
Similarly, for the non-branched skeleton, there must be a double bond. But it can be in the center or at the end. That gives us two more structural isomers.  
Examples: (Reaction Heat...think of it as balancing a financial account, reactants require energy to break up, products supply energy to do this, what energy makes this all balance?) Energy released or energy input to the reactants?
What's expected for geometrical isomers for these two?
There is more than one geometrical isomer that can be constructed at first.