Mechanisms Help

[Patella]

Hello everyone I have a couple of questions on some mechanisms i have been working on. Here are my questions and work:

 

Problem #1

The following cyclic polyene undergoes an ozononolysis reaction at room temperature. Draw the structure of the intermediate formed after the first step. Draw the structure of all organic products formed from the reaction. Indicate products as major, minor, or equal amount.

[Horza2002]

The product drawn in the bottom picture is wrong...you have got two of the carbonyls in the wrong place (I won't tell you which ones as its an assigment)

[Patella]

Okay, I see my mistake. Is this what you mean? The top carbonyl groups should be bonded to the top C's not the other C's. I hope my statement is clearer in my image.

 

 

Thanks!

Edited December 4, 2011 by JessicaOrgo

[Horza2002]

Its not 100% clear, but I think you've now got them in the right place. I assumed you checked what conditions those workups yield? I know that depending on the workup, you can get either the alcohol, aldehyde/ketone or carboxylic acid....so just make sure you've got the right ones.

[Patella]

Yes, i checked the workups. Thank you again.

 

I have another question for a problem i worked all the way already. This one is just for me to understand.

 

A simple and inexpensive way to prepare alkenes is by heating alcohols in acidic solutions. This reaction is prone to rearrangements and often gives unexpected products. For example, the reaction of the following five member ring produces a major product that is a six member ring. Write the complete mechanism involved in the formation of both product. Indicate why each product is the major product and the minor product.

 

 

This is my work with my question:

 

FYI: I have yet to indicate the reason behind the minor and major labeling on my scratch work. I think it has to do with the number of alkyl groups attached to the double bonds. The minor compound only has one alkyl group versus the major compound with two alkyl groups.

[Horza2002]

Have a look at the picture I've attached. If you generate the seconday carb-cation as you have demonstrated, then we can do a rearrangement to so that we no have a tertiary carbo-cation. Tertiary carbo-cations are more stable then secondary ones due to the increase in hyperconjugation. I have also number the carbon atoms so you can see where they move too. One of the carbons of the ethyl group has become part of the ring.

[Patella]

Alright, i understand now. I completely forgot about hyperconjugation, it sounded very familiar and I finally found it on my notes.

Would the answer to the last part of the problem be okay if it was something like this?

The major product is the major product because it has more alkyl groups and it has more hyperconjugation due to them.

 

 

 

I am completely stumped on this question. This is my thought process: I need to find which mechanisms will remove the bromine and add two hydroxyl groups. I think it might go under oxidation/reduction because the end compound has two OH groups. Also, I need to find what synthesis will take the Br away and i cannot find it. There will be two synthesis correct?

 

This is the problem:

Propose a synthesis for trans-cyclohexanediol from bromocyclohexane. Indicated the stereochemistry ofter each synthetic step. If a mixture of products, if produced after a particular step, indicate the major product and the minor product.

 

[hypervalent_iodine]

Alright, so if you work backwards it might become a little more apparent what you have to do. Firstly, ask yourself what ways you know of to make 1,2-diols? From there, you'll have a starting material and it should be fairly apparent how to get that from your bromo-compound.

[Patella]

Well, ladies and gentlemen, I have two last questions. These two are complete duzys and have been throwing curve balls at my goop of a brain.

 

problem #1

Compound A with a molecular formula of C4H6 decolorizes Br2 and produces a precipitate when reacted with permanganate solution. Addition of HCL to A produces two compounds B and C both with the formula C4H7Cl. Ozonolysis of B followed by work-up produces two products, D and F. Ozonolysis of C followed by work-up produces two products, G and H.

 

Draw structures for A, B, C, D, E, F, G, and H.

 

Show the reaction pathway for the formation of each product. Do NOT include the mechanism.

 

 

For problem #1. I have decided that compound A has to be a diene, however after this i get lost because the ozonolysis of B and C are yielding the same products rather than different products. Perhaps i am getting the wrong products from the addition of HCl to compound A.

 

Alright, so if you work backwards it might become a little more apparent what you have to do. Firstly, ask yourself what ways you know of to make 1,2-diols? From there, you'll have a starting material and it should be fairly apparent how to get that from your bromo-compound.

 

Alright, the only one i could find was the epoxide. Do you have any site suggestions where i could find the mechanism for it?

 

Alright, i understand now. I completely forgot about hyperconjugation, it sounded very familiar and I finally found it on my notes.

Would the answer to the last part of the problem be okay if it was something like this?

The major product is the major product because it has more alkyl groups and it has more hyperconjugation due to them.

 

 

 

I am completely stumped on this question. This is my thought process: I need to find which mechanisms will remove the bromine and add two hydroxyl groups. I think it might go under oxidation/reduction because the end compound has two OH groups. Also, I need to find what synthesis will take the Br away and i cannot find it. There will be two synthesis correct?

 

This is the problem:

Propose a synthesis for trans-cyclohexanediol from bromocyclohexane. Indicated the stereochemistry ofter each synthetic step. If a mixture of products, if produced after a particular step, indicate the major product and the minor product.

 

 

Alright, this is what i have for this one, I went backwards as Hyper..._iodine suggested and i came up with this. Is it correct....am i in the correct ball park?

[hypervalent_iodine]

Yeah, but your reagents are a little whacky. As for the cyclohexene, you need to identify what kind of reaction it is and go from there.

[Patella]

alright, i fugure it out. now i'm working on my other ones.

 

This is what i have for problem #1 on post 9:

Edited December 5, 2011 by JessicaOrgo

[hypervalent_iodine]

problem #1

Compound A with a molecular formula of C4H6 decolorizes Br2 and produces a precipitate when reacted with permanganate solution. Addition of HCL to A produces two compounds B and C both with the formula C4H7Cl. Ozonolysis of B followed by work-up produces two products, D and F. Ozonolysis of C followed by work-up produces two products, G and H.

 

Draw structures for A, B, C, D, E, F, G, and H.

 

Show the reaction pathway for the formation of each product. Do NOT include the mechanism.

 

Alright, so first things first. With your C₄H₆ compound - do you know how to calculate double bond equivalents yet? This will give you a huge hint with what sort of compound you're probably looking at if you can work out the DBE. Even if you don't, if you draw a straight chain or branched chain butyl chain, you should be able to work out if you need double or triple bonds and how many of them there will be (it will also tell you if you have a branched butyl chain in this case). Given that the addition of HCl in the next bit gives two products, you can also safely assume one of two options for your starting material, so you should be able to work out what you have as a starting material easily enough from that.

 

Once you have that, it's a case of going through the reactions the question asks and deducing the product. Start by trying to work out what the starting material is first and we'll go from there.

 

alright, i fugure it out. now i'm working on my other ones.

 

This is what i have for problem #1 on post 9:

 

B and C as you've drawn them are exactly the same compound.

Edited December 5, 2011 by hypervalent_iodine

[Patella]

This is the work i have for problem #1:

[hypervalent_iodine]

Your compound G is drawn incorrectly.

 

I don't see H being any different to D, really. Maybe ask your prof. if it's meant to be different?

[Patella]

Do you mind checking these reactions? Do they make sense?

[hypervalent_iodine]

Your use of peracetic acid in the second one is quite odd. On a lab scale, you would usually use m-CPBA or just plain old H₂O₂. Not saying it won't work, it's just not often what you would encounter in a lab.

 

I couldn't make out the last one, but all of the others seem okay.

[Horza2002]

The last one is an ozonolysis and looks fine to me

[Patella]

This problem #2

 

Compound A with a molecular formula of C6H10 decolorizes Br2 and produces a precipitate when reacted with permanganate solution. Hydrogenation with H2 over Pd/C produces B with a formula of C6H12. Reaction of A with peroxyacetic acid produces C, which is highly strained. Hydration of C produces D. Reaction of A with osmium(VIII) oxide followed by work-up produces E which is an isomer of D. C can also be produced by addition of A to bromine water followed by heating. Ozonolysis of A produces a single product E which is a symmetrical diketone.

 

Draw structures for A,B,C,D,and E.

 

This is what I have so far. I am confused because I do not have a mechanism involving heating bromine water. and when I do the ozonolysis of A I do not get the same compound as the E I got from the Os reaction.

 

this is my work

my professor said that this question would determine the women from the girls and the men from the boys....so i'm terrified.

[Horza2002]

I think thats a mistake. A to D is fine, and OsO4 is a well known reagent for the formation of cis-1,2-diols...and D and E are isomers of each other so thats fine (do you know what type of isomers they are of each other?). However, you don't get the diketone product, you only get the diol.

[hypervalent_iodine]

I think that may be a typo. The product from the OsO₄ reaction is definitely going to be a diol, not a dione. The reactions you have drawn there are fine. If the product for your last reaction is meant to be a dione, I suspect that your prof. may have accidentally called it E, when he/she meant to call it F.

[Horza2002]

Thanks Hyper for rewording my post....

[hypervalent_iodine]

The last sentence of your post was a bit convoluted, so I went to the trouble of clarifying it for Jessica. In any case, no need to get so territorial, dear; we're all friends here.