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adamsium
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I, too, can re-iterate; no argument was made. I was quite clear that this was my own view and made no attempt to persuade anyone of anything. No
argument, per se, was presented by me, by your own definition. You, also, have not made an argument, but merely unsubstantiated, presumptuous
assertions.
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[Edited on 7/8/13 by bfesser]
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mr.crow
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Quote: Originally posted by driveby40  | Hey all,
I'm new to this forum, someone on Reddit thought you guys might enjoy my YouTube channel. I've been putting some videos together that showcase some of
the work I do in my lab (I'm a grad student at UCLA). My latest video is a Skattebøl rearrangement to form a cyclic allene. Here's the link, lemme
know what you think!
http://youtu.be/EVDQgjFu9BU |
Nice! I love seeing stuff like this! I have to live vicariously since I can't do this stuff in real life very often
BTW why is everyone arguing and talking about philosophy? Knock it off
Double, double toil and trouble; Fire burn, and caldron bubble
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driveby40
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| Quote: Originally posted by bfesser | This is a futile argument. Those who take part will never concede to the reason of the opposing view. Let's all just agree to disagree and stop
spamming. There's no need to take this thread any further off topic.
<strong>driveby40</strong>, I enjoyed watching your other <a href="http://www.youtube.com/watch?v=Z-0EnES_OS4"
target="_blank">video</a> on the preparation of 2-chloro-1,3-dimethyl imidazolidinium chloride (DMC), but it would be nice if you defined the
acronym before just jumping into using it—sorry, this is one of my pet peeves. I'm a little disappointed that you glossed over your
solution to the ring of impure solid product stuck in the Schlenk flask. What did you resort to?
I've <a href="viewthread.php?tid=19098&page=19#pid289005">requested</a> the paper you cited in the video.
[Edited on 6/22/13 by bfesser] |
Yeah I felt bad about that. I think the stir bar stopped spinning for some reason during the reaction and caused that ring of crap (it was as hard as
a rock!). I had done the reaction before and that didn't happen. I tried poking at it with various needles, injecting more solvents, etc. I ended up
breaking off a piece of the flask in the process so I just quickly capped it and cut my losses by saving what material I managed to collect. It was
kind of embarrassing breaking the glass and whatnot so I edited that out. Haha. Got plenty of pure DMC nevertheless to get to the next step of my
synthesis, but then the subsequent step failed miserably so I gave up on that route. I eventually succeeded making my target compound via an alternate
pathway.
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bfesser
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Thanks to <strong>solo</strong>, <a href="viewthread.php?tid=19098&page=19#pid289064">here</a>'s the paper for the rest of
us.
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Funkerman23
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I agree with Magpie: you have some damn fine equipment at your disposal. Teflon pump, rotovap and that Schlenkline setup was beautiful. Seeing real
air free work was eye opening as well and you seem to know your stuff. If I may ask what degree are you working on? Please make more videos if you
can/ want to!!( subscribed as well). Consider me very impressed.
" the Modern Chemist is inundated with literature"-Unknown
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amazingchemistry
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I'm sorry if this is rather obvious (look at my sig for an explanation  ) but
how can you be sure of the weight of your product to up to three decimal places if your balance seems rather messy and without a draft shield? what is
the error in your yield?
Always remember to check your pride at the door and ask that "stupid" question. Learning comes from having your "stupid" questions answered.
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Magpie
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But he rounds all that uncertainty off to 2 decimal places in the end, ie, "88%."
The single most important condition for a successful synthesis is good mixing - Nicodem
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12AX7
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Nice. The music is a nice touch (90s campiness notwithstanding  ).
But just what *does* it smell like?
Tim
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amazingchemistry
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plus or minus what? The thing is, an error of +.01g would have resulted in a 1% increase in yield. You can call this nitpicking, but why teach things
like error analysis or significant figures at school if we're just going to round our numbers and call it done? I once watched a physics lecture by
Walter Lewin, and one thing he said left a deep impression. He said: "Any measurement that you make without a knowledge of its uncertainty is
completely meaningless." So what's the uncertainty in his measurement?
Always remember to check your pride at the door and ask that "stupid" question. Learning comes from having your "stupid" questions answered.
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driveby40
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| Quote: Originally posted by 12AX7 | Nice. The music is a nice touch (90s campiness notwithstanding ).
But just what *does* it smell like?
Tim |
It smells strong and penetrating, detectable at even dilute quantities. Very unique smell not found in nature as far as I know. It's similar to
gasoline, with an almost cloying sweetness and even an onion-like finish. Similar to dicyclopentadiene if you've ever smelled that.
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driveby40
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| Quote: Originally posted by amazingchemistry | | plus or minus what? The thing is, an error of +.01g would have resulted in a 1% increase in yield. You can call this nitpicking, but why teach things
like error analysis or significant figures at school if we're just going to round our numbers and call it done? I once watched a physics lecture by
Walter Lewin, and one thing he said left a deep impression. He said: "Any measurement that you make without a knowledge of its uncertainty is
completely meaningless." So what's the uncertainty in his measurement? |
Keep in mind that I was doing the experiment to produce a maximum amount of product, not to determine the exact yield. In order to use the more
accurate scale, I'd have to use a smaller, lighter flask and face an inevitable loss in yield during the transfer. 88% on that scale, might very well
be off by 1% (probably moreso due to temperature variation than air currents). I've calibrated that scale and its usually accurate within 0.005g for
my calibrated weights.
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bfesser
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| Quote: Originally posted by amazingchemistry | | You can call this nitpicking, but why teach things like error analysis or significant figures at school if we're just going to round our numbers and
call it done? |
For Analytical Chemistry—this is Organic Chemistry.
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amazingchemistry
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thank you for the answer  I realize now that it does depend on what one is trying
to accomplish. Though I'm sure you would want to calculate your overall yield at the end of the process, and 1% errors pile up fast in multi step
synths.
Always remember to check your pride at the door and ask that "stupid" question. Learning comes from having your "stupid" questions answered.
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bfesser
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From one batch to the next, yields can very widely in organic chemistry. Physical losses can be minimized, but some reactions are just plain
temperamental. It's often a lot more about what you synthesize/isolate than how efficiently. That's left to the chemical and process engineers.
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Magpie
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Those engineers are going to want to know how efficient the process can be before they spend millions of dollars on building a plant.
So they will do optimization and pilot studies first. 
I would like to ask the OP where he obtained the cyclopropane dibromide precursor. Was this made in-house or purchased? If made in-house, what were
the steps?
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[Edited on 7/8/13 by bfesser]
The single most important condition for a successful synthesis is good mixing - Nicodem
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driveby40
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The dibromocyclopropane is made in house from very cheap, commercially available chemicals. Just mix cyclooctene, potassium tert-butoxide, and hexanes
together at 0°C, then add bromoform dropwise. Let it warm and stir overnight. Like the Skattebol rearrangement, the mechanism also involves a carbene
intermediate. Ive attached a pdf to show this explicitly.
Attachment: MECH.pdf (339kB)
This file has been downloaded 457 times
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[Edited on 7/8/13 by bfesser]
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Magpie
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Thank you for explaining this and showing the mechanism. I find it amazing that a cyclopropane, with all its ring strain, can be made so simply.
That shows the power of a carbene, I guess.
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[Edited on 7/8/13 by bfesser]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Heuteufel
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Nice.
But I don´t like the way you drew the addition of the dibromocarbene to the double bond. The addition of a singlet carbene is a [1+2] cycloaddition
and as such a concerted reaction (one step) ... and the representation of the carbene with partial charges is also very misleading. Sorry for the
nitpicking, but I could not resist.
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