Rules of the Day 320N

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

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

3. 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.

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

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

6. 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.

7. 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).

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

9. 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.

10. Both starch and cellulose are polymers of glucose, but starch has the alpha (axial) glucose linkages so it is bent and therefore not rigid (potatoes). Cellulose has the glucose monomers linked via beta(equatorial) glucose linkages so it is flat and the chains can pack together nicely to create rigid cellulose (wood). Click here for a molecule of the day that discusses most of this..

Homework:

No more reading assignments this semester!!
Many students have difficulty understanding how to think about "equivalents", how to balance certain equations like the Claisen condensation, what do we mean by H3O+ and knowing when to use hydroxide versus ethoxide. Here are some short videos to help you with any of these: How to think about "Equivalents" when using base in enolate reactions (7:17 minutes) Correct video for How to think about "Equivalents" when using base in enolate reactions (3:29 minutes) How to balance a Claisen reaction equation (5:06 minutes) What do we mean by H3O+ (2:52 minutes) When to use NaOH vs. NaOEt (7:35 minutes)
There is no daily quiz because of the exam.

When you are ready you can work on a practice homework that will help you prepare for the final. You will not turn it in. Click here for the questions and click here for the answers.