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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: odicon on October 31, 2009, 09:02:20 PM

Title: Three organic Redox-related questions I do not understand
Post by: odicon on October 31, 2009, 09:02:20 PM
Could anyone please shed a light on these? I've looked at them for so long but have no clue.
Thanks in advance.

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Is it "A=D<B=C<E=F"? It's hard to tell because the number of C's are different for each one.



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Is it "oxidation" or "neither"?  I know it's not reduction for sure.


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I am completely lost on this one. How can you tell whether something produces alcohol? I know the reagent gets rid of "=O" but.. seriously.. how?



Thank you so much.
Title: Re: Three organic Redox-related questions I do not understand
Post by: Dan on November 01, 2009, 07:27:26 AM
I think Q1 is fine.

In Q2 there is a typo, there should be a disulfide bridge in the product-

ie. RSH + HSR ----> R-S-S-R  (but the question gives R-S-R)

For Q3, review the chemistry of LiAlH4 (textbook is better, but the basics are here (http://en.wikipedia.org/wiki/Lithium_aluminium_hydride#Use_in_organic_chemistry))
Title: Re: Three organic Redox-related questions I do not understand
Post by: odicon on November 01, 2009, 11:34:31 AM
hey Dan, thanks for your reply!  :)

Do you think Q2 (assuming it is R-S-S-R) should be oxidation since it lost H's?


Also, So according the Wikipedia page... so does that mean LiAlH4 only reduces esters and carboxylic acids? Not anything like carboxylate?
Title: Re: Three organic Redox-related questions I do not understand
Post by: Dan on November 01, 2009, 06:23:34 PM
Quote from: odicon on November 01, 2009, 11:34:31 AM
Do you think Q2 (assuming it is R-S-S-R) should be oxidation since it lost H's?

I would say so, yes.

Quote
Also, So according the Wikipedia page... so does that mean LiAlH4 only reduces esters and carboxylic acids? Not anything like carboxylate?

Two things, first off - the article I linked to gives the reactions of LiAlH4 with aldehydes, ketones, esters, azides, carboxylic acids, nitriles, amides and epoxides. It is not limited to carboxylic acids and esters.

Secondly, the first reaction that happens when a carboxylic acid comes into contact with LiAlH4 is an acid-base reaction that produces the corresponding lithium carboxylate, which is then reduced - so carboxylates will be reduced by LiAlH4. This reagent will reduce pretty much anything, it is extremely powerful - try to identify the product you would get in each case for Q3.