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Homework Help: Organic Compounds

  1. Sep 7, 2006 #1
    Question: The synthesis of an organic compound typically involves a series of reactions, for example, some substitutions and some additions.

    a) Plan a reaction beginning with a hydrocarbon to prepare 1,1,2-trichloroethane

    b) What experimental complications might arise in attempting the reactions suggested in part A?

    My answer:

    a) Well first I used ethyne as my hydrocarbon, added Cl2 to make 1,2-dichloroethene (addition reaction).

    Then I would use the 1,2-dichloroethene and add hydrogen chloride (HCl), and it would be an addition reaction that would become 1,1,2-trichloroethane.

    Can someone verify my answer ...

    b) The only experimental complication I can think of is that during the first step (ethyne + chlorine -> 1,2-dichloroethene) the chlorine may stick to one carbon and make 1,1-dichloroethene...but does that make a difference anyway
  2. jcsd
  3. Sep 7, 2006 #2
    well about making 1,1-dichloroethene... it probably won't happen. For if you were to make 1,1 dichloroethene then two other atoms would have to be on the 2 position which isn't likely to happen unless there is excess Cl2 around (but then you get 1,1,2,2 chloroethene). one thing to think about (probably won't matter) is the cis and trans you would get from this reaction.

    As for the adding of H-Cl how would you control the chlorine going to the 1st carbon. I believe that this follows Markovnikov orientation and would put the chlorine on the second atom making 1,2,2-trichloroethane
  4. Sep 7, 2006 #3
    But 1,2-dichloroethene looks like: Cl-CH=CH-Cl

    Both carbons contain same number of hydrogens so H-Cl would just have to add itself on either one (wont make a difference cause if you read it forwards and backwards its the same). Markonikovs rule says that "rich get richer" but both carbons have the same amount of hydrogens...

    So wouldn't 1,2,2-trichloroethane be the same as 1,1,2-trichloroethane...cause if you are reading 1,2,2-trichloroethane from right to left...
  5. Sep 7, 2006 #4


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    You may have subsequent polymerization with the dichloroethene, also be concerned about rearrangements in general, reactions with water, and reactants should be added with regard to stoichiometry (don't add reagents in excess for any of the steps.
  6. Sep 7, 2006 #5
    yes, my mistake...must read more carefully...or not do it in my free time at work
  7. Sep 8, 2006 #6
    Sorry, but I don't quite understand what "subsequent polymerization" really means...

    Going off topic a bit: Are there any good chemistry books/text books that are good for reinforcing what i'm learning (I'm doing grade 12 chemistry in high school using the Nelson Chemistry 12 text book - science.nelson.com)

    I live in Canada...
  8. Sep 8, 2006 #7


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    I don't believe that the polymerization would be too much of a problem, however, you should mention that the experiment should be regulated for its stoichiometry, that is, be sure not to add any excess of the reagent for any particular step.

    When I was a freshman in college, the text the Chemistry by Raymond Chang, you might want to check out the more recent edition of this text, or you can buy the older editions on ebay from someone who is wanting to sell it for as little as 5.00.
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