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very confused on thsi chem concept

Discussion in 'DAT Discussions' started by arpitpatel86, Jun 18, 2008.

  1. arpitpatel86

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    what are the postitions occupied by the bromine atom and the tert-butl group respectivvely in the most stable conformation of trans-1-bromo-3-tert-butl cyclohexane....
    A. Br-axial, t-butyl axial.
    B.bromine equatorial- and t-butyl equatorilal,
    c. brominie axial, t-butl equatorial,
    d. bromine equatorial, tbutl axial
    the answer was C...but if u look on destroyer 64it showed that (cis) 1-tbutyl-4-iodocyclohexane had the I in the axial and t-butyl group equatorial and this was CIS....so shouldnt the trans in this question both be equatorial or axial?

    all of the following chairs rep cis 1,4 dimethylcyclohexane except.....
    A. a chair with both methyl being axial....
    B a chair with one methyl axial and one methyl equatoria

    the answer was A......so if a cis represent one equatorial and one axial.....then why wasnt the answer to queation 1. B for both bromine and t-butlyl to be equatorial?
     
    #1 arpitpatel86, Jun 18, 2008
    Last edited: Jun 18, 2008
  2. sl2obel2ts

    sl2obel2ts i like tomatoes
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    draw it!
    t-butyl is huge! so br needs to be trans (or otherside of chair). t-butyl is bigger so it takes priority and is equatorial. then br has to be axial.
     
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  3. arpitpatel86

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    why isnt it called a cis then bc this looks exactly the same as number 64 of destroyer.... (cis) 1-tbutyl-4-iodocyclohexane had the I in the axial and t-butyl group equatorial and this was CIS....so shouldnt the trans in this question both be equatorial or axial?


    only diff is that iodine was axial on that and in this one bromine is axial......however destroyer one was CIS adn this is TRANS why?
     
  4. Orgodox

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    One is 1,3 this one is 1,4
     
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  5. theedaddy77

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    if u did cis 1,3 (w/e) cyclohexane and u drawed the chair wouldn't there be 2 different chair that would have different stablitizes hence not the same thing.... therefore on the DAT how do we know which one they would refer to? (if u do it u should get a chair that has both axial and another both equitoral)
     
    #5 theedaddy77, Jun 18, 2008
    Last edited: Jun 18, 2008
  6. harrygt

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    Theedaddy, both answers are correct and make sense. What you really need to do is start drawing the cyclohexane CHAIR configuration, and practice. There is a huge difference between 1,2 - 1,3 - and 1,4 compounds. Being axial and equatorial has nothing to do with cis and trans. in one of them the cis might give you an axial and equat while in the other one the cis might give you two equat, and etc... don't make any relations between being cis- trans and axial-equat .

    read this till I get to answer each of your questions separately.
     
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  7. harrygt

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  8. harrygt

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    Because as you said, one of them is 1,4 and the other one is 1,3. That is what makes this huge diff. Don't try to make relations. DRAW the chair for sure. That is the only way of doin it or you will get lost otherwise.
     
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  9. harrygt

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    all of the following chairs rep cis 1,4 dimethylcyclohexane except.....
    A. a chair with both methyl being axial....
    B a chair with one methyl axial and one methyl equatoria

    the answer was A......so if a cis represent one equatorial and one axial.....then why wasnt the answer to queation 1. B for both bromine and t-butlyl to be equatorial?[/quote]

    All right, I'm going bed after this one. As mentioned, draw a chair, number it in a clockwise manner, and put one methyl on the axial position on carbon 1 [note the upward or downward position, it can be both based on your numbering]. now look at your carbon number 4. you have to put the other bromine on C4 in the same direction to have a cys molecule. Is this direction equatorial or axial? As I can see it in my head, it should be equatorial.
    example: you put first bromine on C1 axially toward up. go look at C4 now. The up position will definitely be equatorial.
     
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