terminal vs internal alkene/alkyne

[andyjl]

Internal alkene/alkyne have a higher b.p vs the terminal alkene/alkyne.

How does the m.p compare?

Also what is the chemistry that explains why the internal alkene/alkyne has the higher b.p?

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[fsapien]

I think, in general, the more substituted an alkene/alkyne is, the more stable it is -> higher b.p. I forgot the exact reason for this, but think of it this way: both carbons have to share electrons, so any surrounding (e- donating) groups surrounding them help stabilize the pi bonds.

 

[jeezy]

hes right

 

[andyjl]

I think, in general, the more substituted an alkene/alkyne is, the more stable it is -> higher b.p. I forgot the exact reason for this, but think of it this way: both carbons have to share electrons, so any surrounding (e- donating) groups surrounding them help stabilize the pi bonds.

gotcha.

so does that also mean the melting point will be lower for the internal alkene/alkyne than the terminal alkene/alkyne?

 

[fsapien]

I would think the melting point would be higher for internals as well. But why would a question ever reference a solid->liqid phase shift of an alkane... (I think this is a very minor detail that probably won't be asked).

 

[crhoody12]

Do you have the Kaplan Blue Book? (in the Alkenes and Alkynes section)

pg 362 "Terminal alkenes usually boil at a lower temperature than internal alkenes"

pg 369 "Internal alkynes, like alkenes, boil at higher temperatures than terminal alkynes"

 

[andyjl]

Do you have the Kaplan Blue Book? (in the Alkenes and Alkynes section)

pg 362 "Terminal alkenes usually boil at a lower temperature than internal alkenes"

pg 369 "Internal alkynes, like alkenes, boil at higher temperatures than terminal alkynes"

yes i do have kaplan, and i already know that the internals boil at higher temperature thn the terminals. i just wanted to know the reasoning behind it.