[Aziz Sergeyevich]

Hey,
I have a homework task whereby we must look at each of the following molecules and discuss how a synthesis beginning with the molecules attached could lead to problems of multiple products - through structural isomerism, stereoisomerism, reactive sites etc giving unintended products.
Any asssistance would be greatly appreciated!
Thanks in advance...
Pictures are linked below:
http://tinypic.com/r/1enm8i/6
http://tinypic.com/r/2n7igc4/6
http://tinypic.com/r/24f0cww/6
http://tinypic.com/r/314eao8/6
http://tinypic.com/r/ofvt5k/6

[discodermolide]

Hey,
I have a homework task whereby we must look at each of the following molecules and discuss how a synthesis beginning with the molecules attached could lead to problems of multiple products - through structural isomerism, stereoisomerism, reactive sites etc giving unintended products.
Any asssistance would be greatly appreciated!
Thanks in advance...
Pictures are linked below:
http://tinypic.com/r/1enm8i/6
http://tinypic.com/r/2n7igc4/6
http://tinypic.com/r/24f0cww/6
http://tinypic.com/r/314eao8/6
http://tinypic.com/r/ofvt5k/6

Forum rules say that you must show your own attempts at answering these questions.
We cannot do your homework for you.

[Aziz Sergeyevich]

Forum rules say that you must show your own attempts at answering these questions.
We cannot do your homework for you.

I have begun researching these molecules, and have acquired a great knowledge of processes which could affect each causing unwanted by-products and was merely seeking another avenue in which I could reaffirm these. For example, in molecule one (the first link posted) the Bromine is electron rich (negative) and has a higher electronegativity which makes it susceptible to being replaced. Molecule two also has several double bonds which contain a high concentration of electrons making it open to an electrophile.

Believe me, I have well and truly attempted my homework!

[discodermolide]

Forum rules say that you must show your own attempts at answering these questions.
We cannot do your homework for you.

I have begun researching these molecules, and have acquired a great knowledge of processes which could affect each causing unwanted by-products and was merely seeking another avenue in which I could reaffirm these. For example, in molecule one (the first link posted) the Bromine is electron rich (negative) and has a higher electronegativity which makes it susceptible to being replaced. Molecule two also has several double bonds which contain a high concentration of electrons making it open to an electrophile.

Believe me, I have well and truly attempted my homework!

Ok, share it with us.

[Aziz Sergeyevich]

I just explained my general understanding of some of the molecules. I am not asking for you to do my homework for me, rather a few hints to ensure I go in the right direction.

[discodermolide]

I just explained my general understanding of some of the molecules. I am not asking for you to do my homework for me, rather a few hints to ensure I go in the right direction.

If you post your attempts we will have a better appreciation of where you are going wrong or not. By the way you can post the pics directly into the forum. See picture.

[Aziz Sergeyevich]

I have basically been looking at each molecule in terms of their electron deficient and electron rich sites. The molecules with double/triple bonds between carbon atoms are electron rich and therefore susceptible to electrophiles like H+ and NO2+ to accept their electrons. I am mainly unsure about how I can prove that a synthesis occurring with these molecules can produce unwanted products. I understand the features of each, as I explained but don't quite understand how this can contribute to unwanted by-products. 

[discodermolide]

I have basically been looking at each molecule in terms of their electron deficient and electron rich sites. The molecules with double/triple bonds between carbon atoms are electron rich and therefore susceptible to electrophiles like H+ and NO2+ to accept their electrons. I am mainly unsure about how I can prove that a synthesis occurring with these molecules can produce unwanted products. I understand the features of each, as I explained but don't quite understand how this can contribute to unwanted by-products. 

Basically you could write a book about this.
Without knowing about the reactions these compounds will be involved in and without knowing what reagents they will be exposed to makes this question almost impossible to answer.

[Aziz Sergeyevich]

I think that is the problem I am having - i cannot quite pinpoint exactly what I am meant to be doing. I think mainly it is to highlight how each molecule can have unwanted by-products through synthesis. For example, ibuprofen had unwanted by-products which were reduced by synthesising ibuprofen with 3 steps instead of 6: http://www.scheikundeinbedrijf.nl/content/Modules/Modulenaam/Files/case.pdf. Our teacher simply said, that prove that there can be unwanted products with these molecules, so from my understanding, adding any other reagent with a reaction that produces very similar products like stereoisomers which are difficult to separate... Problem is, i am unsure what kind of reagents would spark such a reaction.

[discodermolide]

I think that is the problem I am having - i cannot quite pinpoint exactly what I am meant to be doing. I think mainly it is to highlight how each molecule can have unwanted by-products through synthesis. For example, ibuprofen had unwanted by-products which were reduced by synthesising ibuprofen with 3 steps instead of 6: http://www.scheikundeinbedrijf.nl/content/Modules/Modulenaam/Files/case.pdf. Our teacher simply said, that prove that there can be unwanted products with these molecules, so from my understanding, adding any other reagent with a reaction that produces very similar products like stereoisomers which are difficult to separate... Problem is, i am unsure what kind of reagents would spark such a reaction.

Chemists spend their lives finding reagents and reaction conditions which are specific and will produce only the desired compound. The literature is replete with papers discussing this theme. In your case I don't think you can answer this question without knowing which reagents and conditions these compounds will be exposed to. Your teacher should make the question more specific.

[Aziz Sergeyevich]

Okay. Well, for the first molecule I know that if a HBr is added, it could give rise to two isomers. Would you be able to help me in naming these isomers?

[discodermolide]

Okay. Well, for the first molecule I know that if a HBr is added, it could give rise to two isomers. Would you be able to help me in naming these isomers?

Well they would be the following:
2,4-dibromo-1-methylcyclohexane
and
1,2-dibromo-4-methylcyclohexane

[Aziz Sergeyevich]

With these molecules - what is it called when they are both the same molecule but the bromine is placed in a different position?

[discodermolide]

With these molecules - what is it called when they are both the same molecule but the bromine is placed in a different position?

Positional isomers.
See
http://www.chemguide.co.uk/basicorg/isomerism/structural.html#top