An optional review session for the final will be given tomorrow night: Tuesday, April 29 Room: WEL 3.502

For the review session, please bring any extra canned food items you have in your dorm rooms so that I can donate them to the Caritas House

Click here for a copy of the mechanism sheet used in lecture today.

Rules of the Day 4-28-08

1. THE KEY issue with carbohydrates is stereochemistry. The stereochemistry of carbohydrates are based on (+) D and (-) L glyceradehyde. A D-sugar has the same configuration as (+)-D-glyceraldehyde at the chiral center farthest from the carbonyl group. An L-sugar has the same configuration as (-) -L-glyceraldehyde at the chiral center farthest from the carbonyl group. The best way to see this is with Fisher projections. Click here for a molecule of the day that discusses much of this.

2. With Fisher projections, horizontal is toward you, vertical is away from you. Think of it like a teddy bear hugging you. Aaawwwwe.

3. Different stereoisomers of similar carbohydrates can be aldehydes (aldose) ketones (ketose) have different names and generally have 5 (pentose) or 6 (hexose) carbon atoms.

4. Carbohydrates exist in the cyclic, hemiacetal form in solution. Click here for a second molecule of the day that discusses much of this. These are generally shown as Haworth projections. The mechanism involves the same steps at the hemiacetal formation mechanism you learned in Chapter 16.

5. A new chiral center is created (at the anomeric carbon) as the carbohydrate cyclizes, and the OH group can be axial (alpha equals axial for glucose) or equatorial (beta equals equatorial for glucose). For monosaccharides, these two forms are in equilibrium, and interconversion is catalyzed by acid (mutarotation).

6. Cyclic form carbohydrates form either five (furanose) or six (pyranose) membered rings.

7. Carbohydrate monomers can be linked together via acetal bonds, and this linkage can be alpha or beta. (For glucose, alpha is axial) This type of acetal bond is called a glycosidic bond and is named as alpha or beta referring to the stereochemistry of the anomeric carbon and also by the numbers of the ring carbons attached via the -C-O-C- linkage (i.e. alpha 1,4-). Click here for a third molecule of the day that discusses much of this.

Homework: Here is a practice aromatic reactions and synthesis homework. Click here to download a pdf file. You will NOT turn this in, but we have posted answers, click here for the answers. It is here as a tool to get you ready for the aromatic reactions portion of the final. Click here for the last (10th) homework set. You will turn this in Friday, May 2.

Great White Shark Attack near San Diego!!!