Click here for a copy of my lecture notes from today's lecture

Click here for a copy of handout used in class today

Featured Golden Rules of Chemistry: 3. There are two possible arrangements of four different groups around a tetrahedral atom. The two different arrangements are mirror images of each other, a property referred to as chirality and often compared to handedness. 

1. Samples of enantiomers rotate the plane of plane polarized light to an equal extent, but in opposite directions. Rotation is denoted as either clockwise ("+") or counterclockwise ("-"), which replaced the older designations "D" and "L", respectively.

3. We are chiral because our proteins, carbohydrates, DNA etc. are chiral, so different enantiomers of the same constitutional isomer may taste/smell differently to us. Also, for most chiral drugs, only one enantiomer usually has the desired effect.

4. The biochemical literature uses the classic designations of "D" and "L" for key molecules such as amino acids. The common 19 chiral amino acids are all "L". Rather than a reference to rotation of plane polarized light by these structures, this designation refers to a structural connection to L-glyceraldehyde.

5. Acid strength is described by the quantities Ka and pKa. The stronger the acid, the lower the pKa.

6. In an acid-base reaction, equilibrium favors formation of the weaker acid-weaker base (side with higher acid pKa value).

7. For acids that deprotonate to give an anion conjugate base, the stronger acid will produce the more stable anion conjugate base. In other words, when analyzing relative acid strength, compare the relative stabilities of the anion conjugate bases.

8. Use five rules when determining relative stabilities of anions (i.e. when you are predicting relative acid strength) These five rules are actually application of the following two principles: 1) negative charge is neutralized by nuclear positive charge and 2) delocalizing negative charge over a larger area is stabilizing.

a) Across a row of the Periodic Table, negative charge on a more electronegative atom is more stable. (Principle 1)

b) Down a column of the Periodic Table, larger anions are more stable than smaller ones. (This is more confusing than you think, so make sure you understand it). (Principle 2 dominates here)

c) Hybridization: The more S orbital character of the hybridization on the atom that has the negative charge, the more stable the anion (stability of anions is in the order sp>sp2>sp3) Principle 1)

d) Charges distributed over more atoms are better. (Nature hates isolated charges, so delocalizing a charge around by resonance is very stabilizing) (Pinciple 2)

e) Inductive Effect: Electronegative atoms such as F on atoms adjacent to the atom(s) with the negative charge will pull some of the charge away, thus spreading it out and leading to stabilization. (Principle 1 and 2)

HOMEWORK:

Read: There is no reading assignment because of the exam. This text is part of the Longhorn Textbook access program.

There is no quiz because of the midterm tomorrow night.

There is no homework due next week because we will be grading the midterm.

Finish working on the Homework Problem Set 4, due at 10 PM tonight Wednesday, September 23. Note there are Aktiv Learning and Gradescope Questions, and you MUST DO BOTH. Click here to access to the Aktiv Learning electronic homework system.

Click here to access Aktiv learning Homework Problem Set 4

Click here to access Gradescope Homework Problem Set 4

Extra 1st Midterm Practice Homework Problems

Extra 1st Midterm Practice Homework Answers

Here is your second and final Breakout Learning session.  After reading the short handout on organic reaction mechanisms you access by clicking here, click on the link called "Breakout Learning" on the Canvas page margin and follow the directions. You will need to complete the Reaction Mechanisms assignment by next Tuesday evening (Sept. 29) at 10 PM. Note you do not have any homework due next Wednesday while the TAs grade the exam, so this is all you will need to do for this class in the next several days!   Just like last time, the successful completion of the Breakout Learning discussion will earn you 0.5 T Score or raw percentage points on the 2nd midterm. But my bet is it will help you earn far more "real" points than that on the two upcoming midterms and even the final itself because you will understand reaction