Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: LuckyDude35 on September 08, 2004, 02:08:37 AM
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My teacher told us that DMF and THF are both polar aprotic, does that mean the equation done in these will always be SN2 reactions? Thank you for your help, it is GREATLY appreciated!
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they are just solvents,not decisive.
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What role would it play in the problem then? I know the SN2 reactions are supposed to be aprotic and polar and thats what the DMF is. I'm getting a little confused, thanks for the help
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Polar aprotic solvents like DMF and DMSO greatly accelerate SN2 reactions, but that doesn't mean that other types of reactions can't occur in these solvents.
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Ok, then I haev another question. I have a 5-chloro-1-pentoxide ion in DMF and I have to decide whether it is proton transfer, substitution, elimination, or no reaction and write it out. I'm not sure how I woudl tell with this one. Any help would be greatly appreciated, thanks!
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Well, think about the possibilities and think about how likely each one is.
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I'm leaning towards elimination. I'm not sure what would be eliminated though, would it be the Cl, and it just goes off as an ion?
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Well, yeah that's a possibility. What would make that more or less likely? What are the other poissibilities and their pros/cons?
Do you know anything about the structure of DMF and how it accelerates SN2 reactions?
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I really don't know about DMF, my teacher covered SN1, SN2, elimination, and proton transfer all in about 45 minutes and everyone was lost. I know DMF is aprotic and polar but thats about it. Would the Cl react with the DMF? I would think that it wouldn't and maybe the compound comes eliminates the Cl- from it?
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I think that there is a better chance of the Cl being eliminated then the O. He didn't really explain this to throughly and I'm trying to piece it together on my own in order to get these problems done
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Alright, I won't confuse you with the DMF explanation then.
The Cl- won't react with DMF.
Okay, think about it this way:
1) What kind of nucleophiles favor elimination reactions? What kind favor substitution reactions? Which one do you have here?
2) What kind of electrophiles favor elimination reactions? What kind favor substitution reactions? Which kind do you have here?
Then account for what the solvent favors.
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I'm sorry but I am so lost. I know substitution reactions are favored but strong nucleophiles and I think weak electrophiles? I'm sorry but I am getting so confused
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Alright, here is a quick primer:
Substitution reactions:
- typically with strong nucleophiles
- nucleophile is usually small
- electrophile (with the leaving group) must also be small
- favored by polar aprotic solvents
Elimination reactions:
- strong bases that are not good nucleophiles (e.g. t-butoxide)
- large bases
- sterically hindered leaving groups
So based on those primary factors, what would you expect in this case?
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substitution?
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Sounds good to me.
By the way, this is an intramolecular version of the Williamson ether synthesis.
http://www.chemhelper.com/williamsonether.html
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Ok, thanks! This would be SN2 substition correct? And I'm sure this is going to sound dumb but what does it substitute with, the DMF?
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SN1 vs. SN2 is a little less clear cut, but in this case it is almost certainly SN2.
The difference is whether the Cl leaves first and then the alkoxide adds or whether the alkoxide forces the Cl out while attacking the carbon all in one motion.
The "substitution" refers to the carbon with the leaving group attached to it. In this case the net change at that carbon is that the chloride is substituted for an oxygen in the product. In an elimination reaction, however, the chloride would just be gone with nothing taking its place (the carbon would only be attached to three other atoms).
The DMF doesn't directly play a role in the reaction mechanism and it remains unchanged.
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Ohhhh, Ok! Thank you very much for your *delete me* I really appreciate it and will work on these and come back if I have more questions, thanks again!
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No problem.
I'm headed for bed, so your on your own for a while. If you get stuck, check out some of the other pages on that site I linked to above. I think that they have some stuff on mechanisms.
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Hi all:
Can anyone tell me The Heat of combustion of DMF?
Many thanks
wazy
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Hi all:
Sorry need to PUSH!
wazy
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-262.4 x 105 J/kg
by the way we used to have a DMF award at my old work, can you guess what it stands for in the award? hint it was for people who screwed up :D
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Dangerous Mother ...
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Dangerous Mother ...
You got it ;)
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Many thanks to down under.
BTW: I use the data for the calculate diesel consumption in my company thermal oxidizer. Recently, it was much higher, study the causes.
Thanks again.