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 The Lycaeum Forums » Integrate » The Alchemist's Den (Moderator: tryp2fun)Topic:
 Problems - Mechanisms (stereochem)

[delysiduous]

Hey so I was wondering if anyone would be willing to offer me any help on this problem set I'm working on.  I need to provide mechanisms for the following reactions, and explain the observed stereochemistry where applicable.  Two separate steps may be required.  Thanks in advance.  

Oh, and sorry for my poor drawing skills; I don't have a scanner available atm.

A)


B)
 

C)


D)

[pylkko]

I can only speak for myself, but I personally feel a little reluctant to answer such non-specific questions. I mean if you asked something like: "where is the nucleophile?" or: "does this mechanism hold under these conditions?" It could be interesting to talk about it. But to use my free time to do your home work? I don't think so.

[delysiduous]

I can only speak for myself, but I personally feel a little reluctant to answer such non-specific questions. I mean if you asked something like: "where is the nucleophile?" or: "does this mechanism hold under these conditions?" It could be interesting to talk about it. But to use my free time to do your home work? I don't think so.

Lol, I was afraid someone would say this.  I take it if I do some more work and come up with an intelligent question you would not be as opposed to offering assistance.  Will do.

[whateveryouwantmetobe]

Delysiduous, meet arrow pushing.  Arrow pushing, meet delysiduous.  Although I realize you just put this online, make sure in your own drawings you put the hydrogens and electrons on too so you know where everything is.  Those two are after all responsible for most of the magic in organic reactions.  One of the first things I do when I look at this is ask u's question "what is the nucleophile?" (identifiable by the electrons) and then ask myself where it moves to in the final structure.  Then start pushing arrows until you get there, just make sure you don't break the rules or skip steps.  

Those structures are a bit off the wall though.  I'd have to guess your professor does natural product work.  

[delysiduous]

Those structures are a bit off the wall though.  I'd have to guess your professor does natural product work.  

Yea, it's a little bit more advanced of a class.  I know how to do mechanisms lol, I got a B in orgo.  That was 3 years ago though, this class is Structure and Reactivity in Organic Chem.  This problem set is on stereochem and pericyclic reactions.  This was the last problem in the set; I hadn't got up to it yet but it looked hard so I just posted it to see what people thought. 

I guess I'll see when I get up to it.

[whateveryouwantmetobe]

Jeez dude at least try it first.  No one is here to get your education.

[prolixity]

What book are you using?  I find Grossman's "The Art of Writing Reasonable Organic Reaction Mechanisms" to be very useful.

A couple tips which you probably already know:

1) Identify HOMO and LUMO for each step
2) Balance the equation before you start your work
3) Sometimes the product given won't be fully worked up - IE will be conjugate base of final product.
4) Number your carbons in product and reactant
5) Make a table of bonds created and bonds broken (ignore H or it will just get confusing)
6) Resonance, Inductive effects, Sterics (in that order)
7) Always think about neighboring group participation when you get stuck

[delysiduous]

Thanks for the advice, ix (pbuh).  We are using Modern Physical Organic Chemistry, Anslyn/Dougherty.  They are pretty progressive; very critical of old terminology and when I tried looking up some of the stuff on Google, the book was like the second out of four sources that mentioned what I searched for.

[tryp2fun]

The first one is a simple Diels-Alder. 
The second one is a retro 2+2 cycloaddition. 
The third one is a retro 2+2, followed by a cyclization of the resulting quinodimethane with the diazoalkane.
The fourth one is a divinylcyclopropane rearrangement, similar to a Cope.

I have used Bernard Miller's book, Advanced Organic Chemistry: Reactions and Mechanisms, to teach graduate courses in organic reaction mechanisms before.  Grossman's book is OK, but I have not used it.  Audrey Miller's book, Writing reaction mechanisms in organic chemistry, is another good one that I have used as a supplementary text.

[delysiduous]

The first one is a simple Diels-Alder. 
The second one is a retro 2+2 cycloaddition. 
The third one is a retro 2+2, followed by a cyclization of the resulting quinodimethane with the diazoalkane.
The fourth one is a divinylcyclopropane rearrangement, similar to a Cope.

I have used Bernard Miller's book, Advanced Organic Chemistry: Reactions and Mechanisms, to teach graduate courses in organic reaction mechanisms before.  Grossman's book is OK, but I have not used it.  Audrey Miller's book, Writing reaction mechanisms in organic chemistry, is another good one that I have used as a supplementary text.

Thank you kindly.  Yea, I'm not a grad student, but my course (345) is cross listed with 504, which is a graduate course.  She's nice enough to give the undergrad and grad students separate problem sets though, so I guess that's cool. I'm supposed to be at an advantage since I've already taken pchem and some of the students are in pchem now, but to be perfectly honest I don't how I pulled off a B in that course, I hated it and didn't understand most of it.   I miss orgo...    And synthesis and spectroscopy lab, that was the best.  Pchem labs were hellllllll.

[TAPPER]

Hey hey - good to see your still at it dely. Sorry I can't offer much help, Chem 1 & 2 are just a fading memory and well below the level your working at. I do have a life long friend who teaches tho. (PhD in Org) If you are ever up against it drop me a line but remember he doesn't move fast. (must be all his loot generating crazy drag) 

Peace,

TAP