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Cis/Trans isomerism in Alkenes

  1. Nov 14, 2009 #1
    Hey,i just need someone to check my answers :)

    Which of these can exist as cis/trans isomers?
    a.1-pentene
    b.2-pentene
    c.1-chloropropene
    d.3-chloropropene
    e.1,3,5-hexatriene
    f.1,2-dibromocyclodecene
    g.propene
    h.3-hexene
    i.2-hexene
    j.2-methyl-2-butene

    I solved it & my answers are c,e and h.Is this correct?
    & about 1,2-diboromocyclodecene..I wasn't able to draw a cis/trans structure.Can someone please illustrate?

    Thnakyou :)
     
  2. jcsd
  3. Nov 14, 2009 #2
    c, d and f seem to have ambiguous names to me. Whilst you have locants for what I assume is the halogen in each case, you don't for the alkene. e and h certainly exist as cis / trans pairs, but you're still missing some. Can you draw each of them out?
     
    Last edited: Nov 14, 2009
  4. Nov 14, 2009 #3
    These are the names given in my textbook & we're supposed to solve accordingly.I drew each one of them..But some of them seemed to have Z/E isomerism since none of the substituants around the C=C are similar.
     
  5. Nov 14, 2009 #4
    Oh & btw..when there are no locants for the alkene..then we're supposed to assume it as 1.
     
  6. Nov 14, 2009 #5
    Thanks for clarifying the locant situation - in that case all the ones you have so far are correct.

    OK, let's take for instance (i). What do you have at each end of your double bond here?
     
  7. Nov 14, 2009 #6
    On the first C there is H & CH3 & on the second C there is H & CH2CH2CH3.
    So there is cis/trans isomerism with respect to H.Oh yes! I missed that one.Can u please point out the rest that ive got wrong? & ill draw them out.You'll save me a lot of time.Cuz we also have to draw each isomer.
     
  8. Nov 14, 2009 #7
    & 1,2-dibromcyclodecene also has cis/trans.I just didnt know how to draw it.
     
  9. Nov 14, 2009 #8
    That won't really help, but can you see another compound that has the name 2-(something)ene, perhaps?


    What does the name cyclodecene imply to you?
     
  10. Nov 14, 2009 #9
    Ok,so i checked each and every one again & the one that i missed is 2-pentene.Is there any other one i missed?
    Cyclodecene is a cycle of 10 C & with one double bond.But i just couldnt draw the cis/trans representation..I was thinking maybe the trans rep. should be two cycles instead of the one 10C cycle?
     
  11. Nov 16, 2009 #10
    No, that's your lot. Both (E) and (Z) cyclodecenes are one ring, except in one the olefin is cis and the other, trans; just like you've been doing for all the other compounds. How are you drawing your 10-membered ring?
     
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