An EK Organic Chemistry Question

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15+ Year Member
Oct 12, 2003
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In EK MCAT Organic Chemistry 4th edition, Page 26 Question 21, does anyone know how to rotate the bonds in a Fisher Projection to get Anwser B? It is not mentioned anywhere in the EK book.



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This is rather hard to explain just through text. I think the best way I could do it is by drawing pictures. Best bet is to either open a organic text book and find some pictures, go to EK's forum on their website, or ask an organic prof.

I will try and explain it though: all right, optically active compunds are compounds that are chiral. So you are looking fro the compund that has no chiral carbons or has mirror image chiral carbons (meso compund). Meso compunds are not optically active. All of the choices are 2 carbon structures and all have chiral carbons, therefore you are looking for a meso compund. Each carbon has Br, H, and CH3 attached. Each of these groups can be rotated (counter or clock) around their respective carbon. You must find the compund that you can make a mirror image through rotating one of the groups (Br,H,CH3). The only where this is possible is choice B. This is explained in a sentence in the answer section at the end of the book. The whole concept that the question tests is briefly explained in the preceeding lecture. Good Luck.