aamc 7 #165

[Brandon81081]

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wait a second...the hydrogens are drawn in the figure with the plane of the page. So i found it to be R at C-5 and R C-7... but i switched it to S and S because they should be rearranged to go into the page. Where did i go wrong. I chose B.

 

[estairella]

1. The hydrogens are not in the plane of the page, they are pointing back. Even if they were in the plane, that's not enough justification to "switch" your configurations.
2. C-5 is R and C-7 is S, not R and R

 

[Brandon81081]

1. The hydrogens are not in the plane of the page, they are pointing back. Even if they were in the plane, that's not enough justification to "switch" your configurations.
2. C-5 is R and C-7 is S, not R and R

I see. I was under the assumption they are in the plane of the page if they are not show. BUT there are other hydrogens in the illistration that are SHOWN going into the page..thats what confused me

 

[RPedigo]

I see. I was under the assumption they are in the plane of the page if they are not show. BUT there are other hydrogens in the illistration that are SHOWN going into the page..thats what confused me

These atoms are just huge orbs of negative charge (electron clouds). What do negative charges do when they get near eachother?

Answer: They repell

Ok, so look at Taxol on C-5 and C-7. You have two carbons that are in the plane of the molecule, and one molecule facing out towards your face (out of the page). A hydrogen is implied and not drawn in. Because of these negative interactions, it wants to be as FAR AWAY as possible from all other atoms? What SHAPE would allow for this? (i.e. is the molecule linear, bent, tetrahedral, trigonal pyramidal, etc)

Answer: Tetrahedral

Ok, so now that we know the shape-- envision the molecule. Two are in the plane, one is coming directly towards your face (out of the page), where would the hydrogen go to be farthest away?

Answer: Into the page


Then put the lowest priority group in the back (Hint: it already is) and assign your R and S configurations.