explanation - away from me which is obviously wrong I don't...

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To draw a chair for this molecule, you first need to decide upon a "perspective". I have chosen from the "side", as shown. Me Me Et Pr Et Pr look from here The "red" carbons are thus closest to me, and the "blue" carbons are farthest away . The ethyl is on a red carbon and the propyl on a blue carbon. As I look at the chair, the methyl group is pointing down (dashed means down) and is to my "right". Both the ethyl and the propyl are "up" since they are on wedged bonds. Me Et Pr look from here I decided to draw the chair with the methyl equitorial. Both the ethyl and the propyl are thus axial. The ethyl was on the "red" carbon above and is on a red carbon here, since in this perspective, the two red carbons are those closest to me. The propyl is on a blue carbon and is farthest away from me. Me Pr Et If I had switched the ethyl and propyl groups when drawing the chair as shown in the INCORRECDT structure here, then the ethyl group would be farthest
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Unformatted text preview: away from me, which is obviously wrong. I don't know why so many of you drew the methyl pointing up, since it was a dashed bond, thus pointing down, but here is an example of a correct structure with the methyl "up". It takes some mental agility to see that the structure to the left is the same as mine (pre-dental students, are you with me here, can you do it??), and I suspect that many of those who drew the methyl up and got the correct structure were just lucky! Me Pr Et Note that drawing the structure correctly is nothing to do with where you start to number or which direction around the ring you number, it is just being able to see the structure "flat" and being able to translate it to a proper 3-D chair. Looked from the top with the methyl group at the upper end of the structure and pointing down , the ethyl group is on the "right" and the propyl is on the "left" in A, B, C and E, but not in D . A B C D E...
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This note was uploaded on 08/14/2008 for the course CHM 233 & 331 taught by Professor Dr.gould during the Fall '05 term at ASU.

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