IS THIS MECHANISM legit? HELP

[ooscubaoo]

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this is what i wrote on my o chem midterm

my professor had this:

i lost 8 points because i did an "EXTRA STEP." I did a carbo cation rearrangement in it's own step instead of simultaneously when Cl was the leaving group. do you guys think this my mechanism is legitimate? if so, what is a good explanation that my mechanism works...i want a regrade but i can't because i can't back up my mechanism....thanks any info would be appreciated.

 

[aspirant]

Am I the only one who can't see the mechanism?

 

[ooscubaoo]

hey, try pasting the link in a new window and tell me if it opens

http://community.webshots.com/s/image8/3/63/11/146636311NFHKQO_ph.jpg

http://community.webshots.com/s/image10/3/77/74/146637774Pybryn_ph.jpg

 

[Medikit]

this is what i wrote on my o chem midterm

my professor had this:

Did you ask him why he took off the points? You used a resonance arrow/brackets for a tautomer, that's probably why he took off the points.

You are also missing some of your charges which is a no no.

He may also say that the terminal carbocation never exists in this reaction, but you clearly show it existing in some sort of crazy resonance (which it obviously isn't).

 

[ooscubaoo]

the part in the bracket is the EXTRA step i did...i was suppose to do it at the same time as the Cl was the leaving group...that's my question if its possible to do what i did

i'm guessing nooo ?

 

[Medikit]

the part in the bracket is the EXTRA step i did...i was suppose to do it at the same time as the Cl was the leaving group...that's my question if its possible to do what i did

i'm guessing nooo ?

You were supposed to do it as part of the same step yes. And the brackets + double arrow is a no no, that is resonance, you wanted to do a tautomer, but there really isn't any tautomerization between the two either .

How many points was the problem? If it was worth 10 I would have only taken off 2 but put huge red X's through your brackets just to make you feel sad.

 

[edik]

The links don't work either. Says "Forbidden"

 

[ooscubaoo]

i actually didn't write in the brackets, i just wrote that here to show that i did a carbo cation rearrangement after i did the leaving group step.

 

[Medikit]

i actually didn't write in the brackets, i just wrote that here to show that i did a carbo cation rearrangement after i did the leaving group step.

Did you use the double headed arrows?

It's either because of the arrows, or simply because you showed it existing then. And possibly because you didn't show any charges on Fe or Cl. Any of those, but what was it out of? 8 points is a lot and those aren't huge mistakes in my opinion.

 

[ooscubaoo]

yeah i did

 

[kmjannie]

Is it perhaps because primary carbons really hate (+) charges, and the rearrangement to put the charge on the tertiary carbon occurs almost instantaneously? Is that why it has to all occur in one step? To have a primary carbon with a (+) charge on it floating around in solution just doesn't happen - it's too unstable. Perhaps that is why your prof has it all occuring in the same step. Our prof always told us "never draw a primary carbocation...they DO NOT exist for the purposes of this course (which was Ochem).

Ochem was 2 years ago....someone correct me if I am wrong...

Cheers.

 

[ooscubaoo]

^^^^^hmm so there's no good argument to counter that....

i totally agree with what you said, but i'm looking for an explanation that maybe UNDER certain conditions what i did could occur? hehe =)

 

[kmjannie]

Yeah, I think you are up the creek without a paddle. However, my prof did say "for this course" which means that in some other course, the primary carbocation is important...just a matter of finding out what that is. Best of luck.....

 

[Medikit]

^^^^^hmm so there's no goo argument to counter that....

i totally agree with what you said, but i'm looking for an explanation that maybe UNDER certain conditions what i did could occur? hehe =)

If it did occur then you would get more than one product 🙁

 

[ooscubaoo]

Yeah, I think you are up the creek without a paddle. However, my prof did say "for this course" which means that in some other course, the primary carbocation is important...just a matter of finding out what that is. Best of luck.....

i did have a tertiary carbocation, i just did it in a step after. i need a good reason why i isn't done spontaneously.

 

[Benjo]

Dude, from the discussion you were clearly wrong, and know you are wrong, so why the f--- are you trying to get points for your answer? There is a bigger question here than the relative stability of primary carbocations (by the way, how did you not learn this?), and it's, "why the hell are you such a huge douchebag?"

No offense intended, of course.

 

[ooscubaoo]

Dude, from the discussion you were clearly wrong, and know you are wrong, so why the f--- are you trying to get points for your answer? There is a bigger question here than the relative stability of primary carbocations (by the way, how did you not learn this?), and it's, "why the hell are you such a huge douchebag?"

No offense intended, of course.

because 8 points is like 10%... anywaise, i was just asking for help. ppl like you think you're ALL SMART...im glad i'm not going into the medical field...i should stay away from this forum. you ppl are harsh and mean!

 

[Medikit]

because 8 points is like 10%... anywaise, i was just asking for help. ppl like you think you're ALL SMART...im glad i'm not going into the medical field...i should stay away from this forum. you ppl are harsh and mean!

I think the prof took too many points from you unless he stressed it in class. I can give you two reasons why it happens spontaneously, one is that the bromine doesn't simply leave with FeBr3, that is too unfavorable, instead a pimary carbon must attack the partially positive primary carbocation for the bromine to leave. A professor could probably give you better reasoning than that, but how about this answer instead: The reason you KNOW that the primary carbocation never exists is that it only yields one product, if it actually existed there would be two different products.