Boiling point question?

Question

1-butene's boiling point is -6.5
trans-2-butene 's b.p is 1
2-methylpropene's b.p. is -7.
I need to know why? Please give me an explanation!

Answer 1

trans-butene is the only isomer that has any symmetry. What does this mean? Well, it means that the liquid as a whole will have more order in bulk that the other two. As a result the entropy will be higher.

So you should expect an increase in bp in this isomer vs the other C4H8 isomers (although not much - as you can see).

Now which would have more order cis-butene or trans-butene (higher bp?)

hint: http://www.matheson-trigas.com/pdfs/msds/MAT05155.pdf

Answer 2

Boiling Point Of Butene

Answer 3

It appears that the intermolecular forces between the molecues of each compound would be different due to the structures of the molecules. Out of the four carbon chains given, 2-methylpropene will have the lowest bp because it is not a straight chain, as the other two are. This gives less area for dispersion forces to interact with other molecules of the compound. The other two are trickier because the only thing that is different is the position of the unsaturation. It seems that 1-butene is the lower of the two because the double bond is nearer the end of the chain. The causes less hydrogen atoms to be at the end, and will lower the strength of the dispersion forces.

I hope this helps, but you should check this with your chemistry book before you use it, as I am writing this from memory and not checking a specific source

Answer 4

Basically, because of the intermeolecular forces acting on the moelcules, as the chain length of alkenes increases, the boiling point increases and as the degree of branching increases, the boiling point decreases.

2-methyl propene has the shortest chain and therefore lowest bp
1-butene is more branched than trans -2-butene so it's bp is lower.

Answer 5

Van der Waals interaction.

Answer 6

I had asked this same question many times, and didn't get a proper answer

Answer 7

100c