Assigning absolute stereocenter configuration

[kelshie]

So I haven't done organic chemistry in about 3 years, and I can not figure out how to imagine these types of structures in my mind to figure out the stereocenter configuration since the hydrogen (#4) is in the plane of the paper.

Sorry the image is so big. any help with the logic behind figuring these out would be greatly appreciated.

---

Members don't see this ad.

 

[MedPR]

Can't view the image, but just rewrite it with the #4 on the hatch and put whatever was originally on the hatch in the #4's original position. Figure out R or S from there, then switch the configuration.

In other words, if after you move the #4 to the hatch the configuration is R, then the answer is S.

 

[kelshie]

its a ring structure with the 2 groups going up and down on straight lines in the plane of the paper. http://i46.tinypic.com/258t1mx.jpg

 

[MedPR]

its a ring structure with the 2 groups going up and down on straight lines in the plane of the paper. http://i46.tinypic.com/258t1mx.jpg

attach it to SDN. Almost all the upload sites are blocked at my work.

 

[kelshie]

I cant figure out how. Blah.

 

[CodeRedDew]

Do you happen to have the answers? The only way I would go about this problem is to mentally rotate the molecules in your head so that the Hydrogens are facing away from you and count the priority of the groups from there.

I got S and S for the compound on the left. And for the compound on the right I got S and R. (Going from left to right)

Im not entirely sure though, do you have the answers?


Sent from my iPhone

 

[kelshie]

Do you happen to have the answers? The only way I would go about this problem is to mentally rotate the molecules in your head so that the Hydrogens are facing away from you and count the priority of the groups from there.

I got S and S for the compound on the left. And for the compound on the right I got S and R. (Going from left to right)

Im not entirely sure though, do you have the answers?


Sent from my iPhone

Yes, it is S, S for the left and S, R for the right. How do you imagine the H as going backwards with these structures? For the one on the left I got R,R which is backwards.

 

[MedPR]

I think the rule of thumb is down = into the page (hatch) and up = out of the page. I believe it's somewhere in TBR.

 

[CodeRedDew]

I think the rule of thumb is down = into the page (hatch) and up = out of the page. I believe it's somewhere in TBR.

That's right. You could redraw the hagworth projections into the normal line-bond structures and assign R/S that way. For example, with the molecule on the left, you could draw the molecule and have the "OH" on a wedge (indicating it's coming out of the page) and "H" on a dashed bond (for the left stereocenter). And for the stereocenter beside it, you can have the "OH" on a dashed bond and the "H" on a wedged bond. Then assign R/S from there.


Sent from my iPhone

 

[Silo004]

I would convert them into the Fischer projections; assign priority and if priority proceeds in clockwise direction, S; counterclockwise, R.

 

[CodeRedDew]

I would convert them into the Fischer projections; assign priority and if priority proceeds in clockwise direction, S; counterclockwise, R.

Just make sure that if you decide to transfer the molecules into fischer projections then make sure that the "OH and H" that are in the planes of the page go on the horizontal axis of the Fischer projection.


Sent from my iPhone

 

[Mornhavon]

.

 

[MedPR]

I would convert them into the Fischer projections; assign priority and if priority proceeds in clockwise direction, S; counterclockwise, R.

Unnecessarily adding steps to solving problems is not ideal for the MCAT.