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Organic Addition Reactions

  1. Oct 4, 2014 #1
    1. What is the expected major product arising from the reaction of
    2-ethylbut-1-ene with bromine in carbon tetrachloride?

    a. 1-bromo-2-ethylbutane
    b. 2-bromo-2-ethylbutane
    c. 1,2-dibromo-2-ethylbutane
    d. 1,1-dibromo-2-ethylbutane
    e. 1,1,2-tribromo-2-ethylbutane

    Attempt: For this one I'm guessing C but I don't really know for sure.

    2. What is the expected major product arising from the reaction of
    1-phenylcyclohexene with H2O / H+ (catalyst)?

    Select one:
    a. no reaction
    b. 1-phenylcyclohexanol
    c. 1-phenylcyclohexane-1,2-diol
    d. 2-phenylcyclohexanol
    e. phenylcyclohexane

    Attempt: For this one I get E as the alkene double bond will by hydrogenated. The double bonds of the aromatic system will not. Aromaticity is stabilizing. It's not reactive enough to react with H2.
     
  2. jcsd
  3. Oct 4, 2014 #2
    You need to show a bit more effort than just randomly guessing one of the choices.

    For the first one, can you talk about what type of reaction it is? What is the "key" intermediate which will determine the products? What factors affect the formation of the products from the "key" intermediate?

    For the second question, why do you think that an acidified aqueous solution will hydrogenate double bonds? Can you tell us what you know about hydrogenation or alkenes as opposed o addition reactions (reagents, conditions, catalysts etc)?
     
  4. Oct 9, 2014 #3
    Ok so I did a bit of study and got a better understanding of the topic. Bromide addition reactions that aren't aqueous (the tetrachloride isn't used, just to identify that it's not in water) "break" the double bond and replace either side of it with Bromide ions. So for 1. I would go with C as 1 bromide ion would go on the first carbon (replacing the double bond) and the 2nd bromide would go on the 2nd carbon (replacing the double bond).

    For 2. I studied Markovnikov reactions and found that it's similar to the bromide reaction above except that it "replaces" the double bond with an hydrogen and a hydroxide. With that information I choose B as the addition of the OH functional group will make it an alcohol (the hydrogen doesn't really change anything name wise) and because the phenyl will still be connected (Is there any way to figure out if the Hydrogen or the OH is the one connected to the phenyl carbon (carbon 1) or is it random/ unpredictable?

    Hope that's the kind of explanation you're looking for! Thanks for making me look it up, I learn much better that way.
     
  5. Oct 9, 2014 #4
    I agree with your answer but I would advise you to learn the mechanism and work through it. Most importantly to learn what the key intermediate is and why a certain product may be formed instead of another. Your answer, I believe, is correct but the question is relatively straightforward. Instead of thinking about the products and reactants, learn to work through the mechanism of the reaction. This particular reaction can get tricky quickly if you don't know how to work through the mechanism if you need to start thinking about regioselectivity and stereochemistry.

    Take a look through this link.

    There most certainly are models to predict which carbon will get the proton and which will be attacked by water. Again, I suggest you learn the mechanism and get a handle on the trends of carbocation stabilities. I never liked the whole Markovnikov and such addition thing. These questions can all be worked out by understanding a few basic principles and working through the mechanism to determine intermediate stabilities and predict the products.

    See Wikipedia for hydration reactions and page for carbocation stabilities.

    Yes that was much better. I hope you understand we are not trying to be mean, it is the policy of this forum to guide people to find the answer themselves instead of just solving the problems for you.
     
  6. Oct 9, 2014 #5
    Thank you so much for your help, I'll definitely make sure to look at the actual chemistry behind these reactions! So I assume because you didn't say anything that my answer for 2 1-phenylcyclohexanol (b) is correct?
     
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