heat of hydrogenation

Discussion in 'DAT Discussions' started by drzakisadiq, Jul 20, 2008.

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  1. drzakisadiq

    drzakisadiq 2+ Year Member

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    Earlier I posted a thread saying that the more exothermic the heat of hydrogenation, the more stabe it is, and I just wanted to post that I was wrong on that one...

    Correct Part:
    Heat of hydrogenation is the energy released when a pi bond is converted to a sigma bond by the addition of hydrogen. The greater the heat of hydrogenation, the greater the potential energy it has. More potential energy means less stability. Therefore, the least stable molecule will release the most energy upon hydrogenation. THE MORE EXOTHERMIC, THE LESS STABLE.
     
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  3. nzaads

    nzaads 7+ Year Member

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    how do you determine what has the greatest heat of hydrogenation when you are given various alkenes?
     
  4. td4azklz

    td4azklz 2+ Year Member

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    yeah, how do you determine?
     
  5. alanan84

    alanan84 D1 5+ Year Member

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    You would look at where the double bonds are in relation to each other. Cumulated double bonds are the least stable (highest heat of hydrogenation) and conjugated double bonds are the most stable. (lowest heat of hydrogenation) Isolated bonds are in the middle.
     
  6. alanan84

    alanan84 D1 5+ Year Member

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    Also, terminal double or triple bonds are less stable then internal double or triple bonds.
     
  7. td4azklz

    td4azklz 2+ Year Member

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    wWhat are cumulated bonds?
     
  8. alanan84

    alanan84 D1 5+ Year Member

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    Double bonds right next to each other.
     
  9. td4azklz

    td4azklz 2+ Year Member

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    Ok, thanks!
     
  10. Ibraiz

    Ibraiz

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    That means cis will have a higher heat of hydrogenation than trans as cis is less stable than trans. Am I correct?
     
  11. PreDental88

    PreDental88 2+ Year Member

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    Yup
     

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