Recently in Post-lecture Category

The images and data table for the three SN2 transition states shown in lecture today can be viewed here.

First, if you would like to see the MO pictures that I used in class today, check out last year's post on back side attack & HOMO-LUMO overlap (Oct 13, 2008).

There are also a couple of points that I want to add concerning reaction rates (kinetics):

Pity (or envy) poor Alice. In one book she falls down a rabbit hole. When she gets to her feet, she finds bits of food that demand to be eaten ("Eat me!"). And in the next book she steps through a looking glass only to find everything reversed. What is a girl to do?

Well, one thing scientists have always thought is that Alice should not eat any food while she visits the looking-glass universe. All of the protein in Alice's body is built from single enantiomers of chiral amino acids. This means these proteins, including her digestive enzymes, exist as single enantiomers, and they wouldn't be able to digest the mirror-image proteins that get cooked in a looking-glass kitchen. Worse, if she did eat looking-glass food, she might get a terrible stomach ache, and would definitely starve. According to the traditional view, there just isn't any biological value in looking-glass amino acids. A new study, however, turns this view on its head. If you would like to read about this, check out "Expanding Functionality Within the Looking-Glass Universe" (News Perspective, Science, 18 September 2009, 325, 1505-1506).

Slides from today's lecture can be viewed here.

Correction: I was gently informed after lecture that I was wrong about the behavior of CH3CN (acetonitrile) and water. They do mix. I had said they don't. In fact, mixtures of these solvents are routinely used as a solvent mixture for HPLC, a form of chromatography that is closely related to the procedure we will be using in lab next week. My mistake.

I didn't use PowerPoint on Wednesday, but I did show potential maps of several simple molecules that represent the functional groups covered in chapter 8. Slides of these potential maps can be viewed here.

The slides for last Friday's lecture, which covered the last part of Chapter 7 - the stereochemistry of chemical reactions - can be viewed here.

Today's lecture discussed how to name these classes of compounds: RX, ROH, RSH, ROR, RSR. An important point: the complexity of naming/drawing problems will be limited to compounds containing a single principal group.

Slides for today's lecture are located here.

I just came across this in the Editor's Choice section of Science magazine (Oct 2, 2009, p. 19):

Getting a Grip on Nitrogen

Chirality is associated more with carbon than with nitrogen centers, as the latter atoms tend to invert their configurations fairly rapidly on account of their unbonded electron pair. Recently, relatively slow nitrogen inversion was observed in cyclic oligomers of four or six ... amino acids ... on account of hydrogen bonding among the substituents. Mocquet et al. now show that swapping in a single analogous [amino acid] residue that is chiral at carbon disrupts the collective inversion mechanism and thereby dramatically stabilizes the chrial nitrogen conformations throughout the ring.

Notice how the "editor" misuses the word "conformation" when referring to nitrogen "configuration"? Oh well. Probably a physicist.

This was forwarded to me today from the EHS office. Acrylonitrile's formula H₂C=CH-CN. Nerd humor based on a CN triple bond.

"Acrylic" is a common textile material. It is favored for its wool-like feel and commonly used in socks. "Acrylic' is really polyacrylonitrile. Polyacrylonitrile is a nice way of saying polyvinyl cyanide. Do you think anyone would buy socks made from polyvinyl cyanide? If you knock some socks off the shelf in your local discount store, do not run up to the clerk and announce, "There is a polyvinyl cyanide spill in aisle 10'.

Enjoy Fall Break!

A great question came my way right after lecture: can resolving agents by achiral?

The short answer is no.