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2012-09-06 01:58 5031000 Anonymous (paint.png 1266x828 28kB)
Hello /sci/. I started taking OChem about 2 weeks ago, and I have a question. This is not homework, I repeat, not homework, but simply a question of my own speculation. With the molecule, 2,4-diethyl-pentane, could the 4-ethyl group rotate around the sigma bond the carbon's there share to form a benzene ring, and possibly evolve some hydrogen gas as a result? I was just curious while drawing some random molecules. I'll try to draw on paint what I'm talking about. Thanks to anyone who can answer.

2 min later 5031004 Anonymous
not sure if trolling...

8 min later 5031016 Anonymous
Assuming you're not trolling, no. First off, benzene is flat; all the carbon atoms in the ring are in the same plane. Normal carbon chains, despite how they're drawn, are "bumpy" because tetrahedrons. You generally won't get a ring to close, even to make cyclohexane, because the two methyl groups at the ends will repel, they're both surrounded in electrons. If somehow you managed to turn one into a carbocation and the other into a carbanion, then yes, you could close a ring. It'd be a cyclohexane, not a benzene ring, though. If you had some double bonds in there, it would make it much more difficult to get the cation/anion thing going because it would just shift down the chain.

9 min later 5031019 Anonymous
No. That's fucking stupid.

13 min later 5031029 Anonymous
Anyone?

15 min later 5031034 Anonymous
>>5031016 Okay thank you. >>5031019 >>5031004 Like I said, speculation. Calm your nips. >>5031029 New chrome extension doesn't update automatically, now I see.

39 min later 5031097 Anonymous
>>5031034 Sorry for being curt, it's been awhile since Org 1. #1 rule of OChem - count your carbons. Your starting product is a 9-carbon species, your end product is an 8-carbon molecule - you seem to be merging the two carbons at the top. Don't confuse the line drawing with what the molecule actually looks like - there are atoms at the end of each line. Assuming you had the correct starting product, the first step would be a cyclization to get 2,4-dimethylcyclohexane. You can go about this by two ways: Oxidation: The alkyl groups you want to join are ridiculously stable, and are pretty much equivalent to every other carbon in the molecule. Meaning that if you have conditions where those two carbons are oxidized, chances are the rest of the molecule will be, too. Congratulations, you have now created combustion! Your starting material is charred to bits. Nucleophilic attack: you need to make one of the terminal carbons a nucleophile (meaning it has a free electon pair), and the other an electrophile (meaning it wants a free electron pair). Problem is, alkyl groups don't make good nucleophiles OR electrophiles. To make it a nucleophile, you need to strip off a proton while leaving its electron behind - something that even the strongest bases can't accomplish. To make it an electrophile, you need to make the proton leave with an electron pair - and protons are among the shittest leavings groups around. Now try and do that all in the same flask. Once you get it cyclized, I believe there are reactions to convert cyclohexanes into benzene rings, but they require ridiculous amounts of energy, again because alkyl groups are so resistant to oxidation. BTW, your end product is called m-xylene, and is cheap as fuck, because it can be produced from plant pulps.

2 hours later 5031254 Anonymous
>>5031097 Okay, that all makes a good amount of sense to me. Thank you very much; I see where I made some pretty rudimentary mistakes in my initial drawing. I did not think about this thoroughly enough. Have a nice day, if you're still there.

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