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Talk:Paraffins: Difference between revisions
Homolysis by thermal energy
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::Conceptually speaking, we would be looking for graph equivalence here. Although the graph can be represented as a tree, "equivalence" allows any node in the tree to be the root, and the branches from any node can be in any order. --[[User:Rdm|Rdm]] 20:59, 5 December 2011 (UTC)
:::I think deciding to go by graph equivalence answers the isomer question. Stereo isomers have equivalent graphs and so would not be counted. This is what A000602 does. It also answers the question of physically impossible isomers that start at C16. We would count these because we can produce a graph for them, even though they cannot physically exist. —[[User:Sonia|Sonia]] 21:31, 5 December 2011 (UTC)
:::: Wait, what do you mean "cannot physically exist?" --[[User:Ledrug|Ledrug]] 01:27, 6 December 2011 (UTC)
::::: http://www-jmg.ch.cam.ac.uk/data/isomercount/
::::: Seems that when the molecules get highly branched, there's not enough room for all the parts to squeeze in close enough to bond. I don't do this kind of work myself, but these guys seem to have put some thought into it. —[[User:Sonia|Sonia]] 02:20, 6 December 2011 (UTC)
:::::: Ok. Well they were not describing it (either 16 or 17) as impossible to form, it's not a space issue. What happens is that due to the structure and consequently how electrons should distribute to obtain lowest energy state, if you put such a molecule under room temperature, thermal energy alone will be enough to break one of the carbon bonds and split the molecule into two. They can still form, but you can't hold on to a beaker of such material for any meaningful amount of time without refrigeration (they didn't give numbers, so it's hard to tell if that C17 would be stable at absolute zero; C16 would.) --[[User:Ledrug|Ledrug]] 02:50, 6 December 2011 (UTC)
=== stereo-isomers ===
Someone (IP:79.54.58.148) has reverted part of my edit because they incorrectly think paraffins cannot have stereo-isomers. In fact they can, for example C(H)(CH<sub>3</sub>)(C<sub>2</sub>H<sub>5</sub>)(C<sub>3</sub>H<sub>7</sub>) (better known as 3-methylhexane: CH3CH2CH(CH3)CH2CH2CH3) is [http://www.wwnorton.com/college/chemistry/orgo3/ch4/2_methylhexane.htm chiral] and so exists in stereo-isomeric form. If you disagree please discuss it here before I change the page back. [[User:TobyK|TobyK]] 00:09, 1 December 2011 (UTC)
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