Organic Questions

[Got Em]

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1) Would somebody please explain to me this statement? "Both carbons have the priorities oriented in the counterclockwise direction, but both hydrogens are coming out of the page, so their absolute configurations must be R."

I have the EK organic books, but I can't find this explaination anywhere regarding how to prioritize the atoms.

2) I know that "chiral" centers must be SP3 and have 4 different substituents, but what exactly is considered a "different" subsituent? I'm doing some questions with bond-line formulas and I just don't get it.

Thanks in advance.

 

[loveoforganic]

http://www.vanderbilt.edu/AnS/Chemistry/Rizzo/Chem220b/Stereochem.pdf

Decent rundown on assigning priorities and configuration. The problem you're coming across is using a shortcut, however. While you normally position the lowest priority subsituent into the page (away from you), you can also leave it positioned pointing out of the page (toward you). When leaving it positioned pointing toward you, you follow the exact same steps - assign priorites then figure out direction of rotation. However, the configuation you assign will be opposite of what it would be if the lowest priority substituent was pointing away from you.

 

[SpinWiz]

http://www.vanderbilt.edu/AnS/Chemistry/Rizzo/Chem220b/Stereochem.pdf

Decent rundown on assigning priorities and configuration. The problem you're coming across is using a shortcut, however. While you normally position the lowest priority subsituent into the page (away from you), you can also leave it positioned pointing out of the page (toward you). When leaving it positioned pointing toward you, you follow the exact same steps - assign priorites then figure out direction of rotation. However, the configuation you assign will be opposite of what it would be if the lowest priority substituent was pointing away from you.

Great link. Thanks for sharing! I'm finding TBR extremely helpful for Organic along with TPR 'Cracking the CBT' book. Did you use TBR for organic?

 

[loveoforganic]

Yes. It's a very good book. Has too much info if anything though, very detailed.

 

[SpinWiz]

Yes. It's a very good book. Has too much info if anything though, very detailed.

Did you do the organic passages in phases (I, II & III) or all of the passages in one section together?

 

[loveoforganic]

phases

 

[kentavr]

There is a strange thing in your question. Two hydrogens. In order to have stereo configuration R or S, all four substitutes has to be different. If I understand correctly two hydrogen-substitutes cannot make chirality. Or something is missing here.

 

[loveoforganic]

There are two stereocenters