Alkane/alkene/alkyne stability

[GomerPyle]

Hello. I have a question.

Alkanes have a single bond, less energy than alkenes and alkynes which have respectively two and three bonds and higher energy. Higher energy means shorter bonds which means stronger bonds.

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.

I understand how higher bond energy means more unstable, but I don't understand how stronger bonds means it is unstable. Shouldn't stronger bonds be more stable since it takes greater energy to break them?

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[jmbusclas]

Hello. I have a question.

Alkanes have a single bond, less energy than alkenes and alkynes which have respectively two and three bonds and higher energy. Higher energy means shorter bonds which means stronger bonds.

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.

I understand how higher bond energy means more unstable, but I don't understand how stronger bonds means it is unstable. Shouldn't stronger bonds be more stable since it takes greater energy to break them?

You are considering the "triple bond" and "double bond" as a single entity. Recall that the bond is actually made up of one sigma bond and either one or two pi bonds. Those pi bonds are much weaker and much higher in energy than sigma bonds. Remember, it is the pi bond that is reacting.

 

[GomerPyle]

You are considering the "triple bond" and "double bond" as a single entity. Recall that the bond is actually made up of one sigma bond and either one or two pi bonds. Those pi bonds are much weaker and much higher in energy than sigma bonds. Remember, it is the pi bond that is reacting.

makes sense now. thx