[portugal]

I have come across this question and i am not really sure of my answer, would someone be able to tell me if i am correct or how to correct my answer

1. Does the oxidation of (2R,3R)-3-methoxy-2-methyl-1-butanol to its corresponding carboxylic acid interfere with the stereochemistry of the molecule?

Well what i was thinking was that it wouldnt affect the stereochemistry for the reason being that by replacing the hydroxy group with the carboxyl group that there is no change in the actual assignment of priorty numbers on that carbob becuase origianlly rhe -OH group was highest and therefore -COOH group is replacing it and thereofre no change occurs

am i right or have i stuffed it up

[sjb]

The way I see it, there are might actually be two questions here.

1) Does the oxidation of the alcohol affect the configurations at the two chiral centres - are there things like racemisation going on (like for instance if there were an S_N1 reaction going on)?

2) does the oxidation affect the name (and the stereochemical descriptors) of the two chiral centres?

I'm not sure about the first part, it may depend on the actual oxidation employed.

As to the second, a) are you sure that the OH is part of the highest priority group and b) is the oxidation really "simply" replacement of OH by CO₂H?



S

[portugal]

what would you have wroten down as answer to this question because i am lost at the moment

[AWK]

As to the second, a) are you sure that the OH is part of the highest priority group and b) is the oxidation really "simply" replacement of OH by CO2H?

SJB gave you just a hint though it should be: CH2OH by CO2H

[portugal]

Its my first week in organic chemistry 2 at usyd and all in need is a good in depth explanation of this problem to help me grasp the course and concepts more better as text/lectures are useless

[azmanam]

start here

http://www.cem.msu.edu/~reusch/VirtTxtJml/alcohol2.htm#alcrx4
http://www.chemguide.co.uk/organicprops/alcohols/oxidation.html
http://en.wikipedia.org/wiki/Oxidation_of_primary_alcohols_to_carboxylic_acids
http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch15/ch15-4-6.html

and recheck your priority assignments in the starting material and product.

I agree with sjb.  the question is different depending on what is actually being asked.  I think your question is probably #2 in sjb's response.

[sjb]

Note, this is based on my knowledge and understanding (or probably lack of). I'm not sure at what level you're at, but from your posts I'm assuming this is around early-middle undergraduate degree level, apologies if not the case. With that caveat and assuing this could be an exam question to take ~ 20 mins, here we go...

1. Does the oxidation of (2R,3R)-3-methoxy-2-methyl-1-butanol to its corresponding carboxylic acid interfere with the stereochemistry of the molecule?

As usually formalised, oxidation of (2R,3R)-3-methoxy-2-methylbutan-1-ol will result in a 2,3-disubstituted butanoic acid. Whilst it is unlikely that the oxidation will affect the beta chiral carbon (the one with the methoxy group attatched) it is possible that the oxidation may affect the alpha position. If the oxidation merely formally removes the methylene protons of the primary alcohol and replaces them with a oxygen atom, then the alpha position of the acid becomes one of S configuration, and so the product is (2S,3R)-3-methoxy-2-methylbutanoic acid (carbon attatched to 3 oxygens has higher priority than carbon attached to 1 oxygen).

(This is essentially what I was trying to establish by part 2 - although the carbon-carbon bond has not broken, the priority of that branch has changed and the name of the centre has also been affected)

Should some racemisation occur then the C₂ epimer has the name (2R,3R)-3-methoxy-2-methylbutanoic acid...

(This starts to touch on part 1 and is vague as I don't honestly know if it's likely in this case)

...complete with drawings to show starting material, the two diastereomeric products and how I assigned R and S to the centres.

END

It is also plausible oxidation could occur by insertion of CO into the C-O bond of the alcohol (this is part of what I was trying to establish when asking if you were sure that the oxidation was replacement of -OH by -CO₂H. (I certainly covered the basics of this i.e. "it happens but we'll go into more depth later" in the first year of my degree, I don't know how "organic chemistry 2 at usyd" would correlate). How do you think this would this affect the answers if this was the oxidative pathway in operation?

Note to moderators, if you want to delete or hide this by all means do so, just let me know or copy the text into a PM, I don't want to have to write it out again in a couple of days 

[portugal]

Yea thanks very much but last nite after rethinking i worked it out because i looked at my messy strucutres and noticed i was assigning the priorities in wrong orders lol but i did end up finding that it becomes an s configuration