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How is this correct? (Organic; Stereochemistry)

  1. Oct 23, 2011 #1
    Draw Newman projections depicting the (R)-enantiomer of each of the following:
    a) 1-bromo-1-chloroethane
    b) 1-bromo-1-methoxypropane


    Now, I am SURE that I am mistaken, but isn't that an (S)-enantiomer for each? Assigning priorities:

    For a) Br > Cl > CH3 > H....right? So, wouldn't the (R)-enantiomer have the Br and Cl switched? With Br on the top, you have priority 1 at the top, 2 at the bottom right, 3 in the middle, and 4 on the bottom left. Isn't that a clockwise direction, with 4th priority facing away from us? Or, is that H facing towards us...help!

    Same goes for b, I switched the OCH3 and the Br...Something is really messing me up that is causing me to do this. Thank you in advance!
  2. jcsd
  3. Oct 23, 2011 #2
    When you assign R and S, you let the 4th priority group face away from you. I've been picturing it so that the central atom, presumably carbon, is in the middle and the 4th priority atom, presumably hydrogen, is eclipsed by the central carbon and points directly away from you.

    anyway, I'm pretty sure a is S and b is also S too. maybe the key is wrong or we're both making the same mistake?
  4. Oct 24, 2011 #3
    Yeah, I really have no idea. A lot of answers have been wrong in the past, but for this chapter, it really grinds my gears not to have faith in the answer key.
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