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Old 07-20-2008, 02:03 PM   #1
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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...

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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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Old 07-22-2008, 08:28 AM   #2
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how do you determine what has the greatest heat of hydrogenation when you are given various alkenes?
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Old 07-22-2008, 03:25 PM   #3
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how do you determine what has the greatest heat of hydrogenation when you are given various alkenes?
yeah, how do you determine?
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Old 07-22-2008, 03:29 PM   #4
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yeah, how do you determine?
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.
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Old 07-22-2008, 03:31 PM   #5
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Also, terminal double or triple bonds are less stable then internal double or triple bonds.
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Old 07-22-2008, 03:32 PM   #6
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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.
wWhat are cumulated bonds?
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Old 07-22-2008, 03:33 PM   #7
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wWhat are cumulated bonds?
Double bonds right next to each other.
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Old 07-22-2008, 03:44 PM   #8
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Originally Posted by alanan84 View Post
Double bonds right next to each other.

Ok, thanks!
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Old 07-19-2010, 06:48 PM   #9
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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?
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Old 07-19-2010, 07:45 PM   #10
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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?
Yup
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