Hydrocarbon K: Structure and Carboxylic Acid Product Revealed

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Discussion Overview

The discussion revolves around identifying the structure of a hydrocarbon K that, upon hydrogenation and oxidation, yields a specific three-carbon carboxylic acid. Participants explore the implications of chemical reactions involving hydrogenation and oxidation with potassium permanganate (KMnO4), focusing on the structural characteristics of K and the resulting carboxylic acid.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that hydrocarbon K is likely an alkene with three carbons, proposing a structure of H3C-CH=CH2, leading to a corresponding carboxylic acid HOOC-CH=CH2.
  • Another participant proposes that K could be a symmetrical alkene, specifically 3-hexene.
  • A different participant questions whether permanganate cleaves double bonds to produce carboxylic acids, recalling examples from textbooks that support this idea.
  • One participant describes a reaction pathway involving dihydroxylation followed by cleavage of the diol, leading to aldehydes that are subsequently oxidized to acids.
  • A later reply shares a specific reaction sequence that was graded as correct, indicating a successful identification of K and the carboxylic acid, but the formatting of the chemical structure was unclear.
  • Another participant acknowledges the confusion regarding the structure's representation, specifically the placement of the carbonyl group.

Areas of Agreement / Disagreement

Participants express various hypotheses regarding the structure of hydrocarbon K and the resulting carboxylic acid, with no consensus reached on a definitive structure. Multiple competing views remain regarding the nature of the hydrocarbon and the reaction mechanisms involved.

Contextual Notes

Some assumptions about the reactivity of KMnO4 and the structural implications of the proposed hydrocarbons are not fully explored, leaving room for uncertainty in the proposed mechanisms and structures.

tipton12
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Having trouble with this one; I've tried working backwards from the three carbon carboxylic acid product, but to no avail. Please help! I can not figure out 'K'.


"A hydrocarbon K adds one equivalent of H2 upon hydrogenation over a Pt catalyst. When K is oxidized vigorously with hot KMnO4, a single three carbon carboxylic acid is obtained. Give the structures of K and the carboxylic acid."

This seems simple but K is giving me a lot of grief.
 
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Well, vigorous reaction with hot permanganate is not still enough for pure hydrocarbons, this is an alkene with single double bond, this is okay. Since decarboxylation won't occur with KMnO4, I think the K hydrocarbon has three carbons. The vinylic hydrocarbon [tex]H_3C-CH=CH_2[/tex] may be the structure for K and the corresponding carboxylic acid may be [tex]HOOC-CH=CH_2[/tex]. I think the carboxylic acid should be like this, since it is principally similar with an aromatic alkane, say, toluene, which can also be oxidized with permanganate to the acid.

I may be wrong, so you will have to finish the remaining work by yourself.
 
Sounds like a symmetrical alkene to me. Probably 3-hexene.
 
Hmm, does permanganate cleave double bonds to give carboxylic acid? I couldn't remember this one. However, this is logical. I remember ozonolysis to produce ketones or aldehydes, so this sounds okay to me.

EDIT: I looked up my textbook and saw the example with cyclohexene to give adipic acid with hot permanganate. So your assumption is okay, I think.
 
Last edited:
I'll play around with both ideas and get back to you on my answers. Thank you both for all your help!
 
Yeah, I think KMnO4 first does a dihydroxylation, much like OsO4, and then cleaves the diol, much like NaIO4 does. The resulting aldehydes are then oxidized to the acids.
 
sorry i never got back to writing my answer. I waited for it to be graded.
This is what I did and it was marked correct:

K ____H2/Pt___K ____Oxidized___KMnO4/heat___ 3-hexene___H2/Pt___hexane w/carbocation on the 3carbon_____warm KMnO4/-OH___>> HO-C-CH2-CH3
ll
O

Thanks for your help!
 
i don't know why my answer posted that way, but the =O is supposed to be on the Carbon attached to the -OH.
 

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