Orgo question!

[flower123]

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So I was watching chad's orgo videos and had a question.
So I know as the chain length increases - the boiling pt of alkanes increases and branching of alkanes lowers the boiling point. I don't understand the effect of branching on the melting point. Are they difficult to pack when they are branched so less stable thus have a ___ melting pt. I am just getting confused because in the kaplan book it says they will have lower melting pt but in the video - chad says that they will have a higher melting pt!! any ideas?

 

[DoCt0rPeTe]

So I was watching chad's orgo videos and had a question.
So I know as the chain length increases - the boiling pt of alkanes increases and branching of alkanes lowers the boiling point. I don't understand the effect of branching on the melting point. Are they difficult to pack when they are branched so less stable thus have a ___ melting pt. I am just getting confused because in the kaplan book it says they will have lower melting pt but in the video - chad says that they will have a higher melting pt!! any ideas?

Branching may lead to supersymmetry, which will allow for the molecule to fit into a crystal much better than a molecule that is unbranched.

Generally, molecules follow the same trend for BP and MP, however, this excessive branching is an exception in that the molecule can fit into a crystal, thusly having a higher MP.


Hope that helps...

 

[orgohacks]

So I was watching chad's orgo videos and had a question.
So I know as the chain length increases - the boiling pt of alkanes increases and branching of alkanes lowers the boiling point. I don't understand the effect of branching on the melting point. Are they difficult to pack when they are branched so less stable thus have a ___ melting pt. I am just getting confused because in the kaplan book it says they will have lower melting pt but in the video - chad says that they will have a higher melting pt!! any ideas?

I wrote a post about this a few weeks ago:
http://masterorganicchemistry.wordpress.com/2010/07/09/chemical-tetris/

hope this helps - James

 

[flower123]

wowww..thanksss!!