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Shweta Thakur posted an Question
June 06, 2020 • 20:22 pm
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30 points
30 points
- IIT JAM
- Chemistry (CY)
Which is thermodynamically more stable alkeme alkene and alkyne plz explain all threee
which is thermodynamically more stable alkeme alkene and alkyne plz explain all threee
3 Answer(s)
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Dinesh khalmaniya 1
The reactivity order depends on the process(as mentioned in the comment). 1) In acid-base reactions, alkynes are the most reactive followed by alkenes and alkanes. This is due to the stability of conjugate base of alkyne by sp hybridized carbon atom. 2)In electrophilic substitution, alkynes are less reactive than alkenes. It is because of relative stability of carbocation formed in the case of alkenes. 3)In case of hydrogenation reactions, alkynes are more reactive than alkenes.
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Suman Kumar
Hope your doubts are clear
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Dinesh khalmaniya 1
hope this will help you 🙏
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Dinesh khalmaniya 1 Best Answer
Alkynes are less stable then alkenes and alkanes despite the bond being stronger. This is not really intuitive, because you'd think that stronger bonds are more stable, correct? But in this case, the stronger bonds in alkenes/alkynes have higher bond energy and thus more unstable than alkanes.
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Suman Kumar
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Suman Kumar
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Dinesh khalmaniya 1
-2 The reactivity is: Alkynes > Alkenes > Alkanes. Alkynes have two pi-bonds between two (or more) carbon atoms, along with a sp-sp hybridised orbital bonding (sigma bond). The pi-bonds can be easily broken to free the valence shell electrons for combining with other atoms. Hence they are the most reactive. Alkenes have one pi-bond between two (or more) carbon atoms, along with a sp2-sp2 hybridised orbital bonding (sigma bond). The pi-bond can be easily broken to free the valence shell electrons for combining with other atoms, but as the number of pi bonds is lesser than Alkynes, they are less reactive. Alkanes have no pi-bonds between carbon atoms. They only have a sp3-sp3 hybridised orbital bonding (sigma bond). For Alkynes to react, first the sigma bonds with Hydrogen (s-sp3 sigma bonds) have to be broken, and only then can other atoms combine. This entails more energy, so Alkanes are the least reactive among the three. This also explains why Alkynes and Alkenes undergo addition reactions, while Alkanes only undergo substitution reaction.