Chem 242 @ Dickinson

Fischer Projections

Today's main point was the Fischer projection. This biochemist's way of drawing three-dimensional carbon atoms is useful but a little awkward at first. Essentially, it reduces down to a few basics: horizontal lines are coming out at you and vertical lines are going back away from you; 180° rotations give you the same molecule; 90° rotations give you the mirror image (and therefore the enantiomer if there are four distinct substituents on the carbon); holding one substituent in place and rotating the other three (either CW or CCW) gives you the same thing. We looked at the method for determining R and S configurations -- put priority #4 at the top by whatever manipulation you need and then look for CW (R) or CCW (S) rotation of 1, 2 and 3.

At the end we started looking at how carbohydrates form six-membered rings and I left you with an assignment for the weekend -- make a model of D-galactose and orient it into position to make a six-membered ring. See if you can determine any relationship between the positions of the -OH groups in the Fischer projections and the orientations of the -OH groups in the chair conformation.

I've added a link for podcasts to the right. I'll talk more about them on Monday.

There are also links for two new problem sets, 14 and 15. There is no key for 14 yet (we haven't talked about all of the material), ps 15 is all about relating two Fischer projections to one another.

posted by DCChem @ 10:47 AM