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    Ok, I'm revising for a test on structure determination and one question is irritating me: here's part of it.

    Compounds C and D, shown below, are isomers of C5H10O
    C is a ketone and D is a cyclic alcohol btw


    (d) Identify a reagent that you could use to distinguish between C and D. For each of C and D, state what you would observe when the compound is treated with this reagent.
    Reagent ……………acidified potassium dichromate
    Observation with C …………………no change
    Observation with D ……………Orange to green
    (3)
    (e) Compound E, CH3CH2CH2CH2CHO, is also an isomer of C5H10O
    Identify a reagent which will react with E but not with C or D. State what you would observe when E is treated with this reagent.
    Reagent ………………The answer is Tollens reagent or Benedicts/Fehlings
    Observation with E ………………Silver mirror with tollens or brick red ppt with benedicts/fehlings






    My problem is that why can't a tollens or benedicts oxidise a cyclic alcohol? Or is it that they can't oxidise secondary alcohols?

    I haven't done this for a few months so would someone help!!?
    Thanks.
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    Compound E is an aldehyde.
    You could oxidise the cyclic alcohol to a ketone, and then easily distinguish between the two using Tollens reagent. Can't think of anything else at the moment.
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    I think tollens reagent is simply not a strong enough oxidising agent to oxidise an alcohol, but it is strong enough to oxidise an aldehyde to a carboxylic acid. As to why that's the case, that would be quite complicated I think.
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    (Original post by Jin3011)


    My problem is that why can't a tollens or benedicts oxidise a cyclic alcohol? Or is it that they can't oxidise secondary alcohols?

    I haven't done this for a few months so would someone help!!?
    Thanks.

    Neither reagent reacts with alcohols, 1º or 2º.

    Tollens and Benedicts react with aldehydes as opposed to ketones.
 
 
 
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