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Homework Help: Organic Chemistry and propanone

  1. Apr 8, 2007 #1
    1)Give a chemical test that can be used to distinguis between separate samples of propanone and propanal. Give a suitable reagent for the test and describe what you would obsrve with propanone and with propanal.

    2) Outline the reaction of propanone with the following reagents. Give the equation for the reaction, the conditions, and the name of the organic product.
    (i)Hydrogen cyanide
    (ii)dodium tetrahydridoborate(III) (sodium borohydride)
    (iii)what type of mechanism is this
    (iv) what feature of the carbonyl group makes this type of mechanism possible? Explain how this feature arises?

    3)Three isomers A,B, and C have the molecular formula C4H8O. All three compouds give an orange precipitate with 2,4-dinitrophenylhydrazine reagent. B and C give a silver mirror when waremed in ammoniacal silver nitratesolution. Write the strcutural formulae of A,B and C.
    Last edited: Apr 9, 2007
  2. jcsd
  3. Apr 9, 2007 #2


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    You need to show some work before we will help. What have you tried with this problem?
  4. Apr 9, 2007 #3
    My idea to the separate samples of propanone and propanal is to use an ammoniacal solution of silve which propanone should show some change(a white precipitate) and propanal does not

    While when propanone reacts with hydrogen cynaide the N-bonds will break and will be attached to propanone

    While the last one I have had no ideas
  5. Apr 9, 2007 #4
    Youre right on the tollens reagent test. Propanal will also give a red ppt with benedicts solution and felhings reagent (of Cu2O).

    On the cyanide reaction, the N-bonds wont break, CN- will act as a nucleophile and attack the carbonyl carbon to form a cynohydrin.

    The NaBH4 will reduce it to alcohol, but I dont know what mechanism makes it possible.

    For the last one, if they give red ppt with 2,4-DNP, then they have a hydroxy group (OH). If they react with tollens reagent (ammonical silver nitrate), then they are aldehydes.
  6. Apr 10, 2007 #5


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    You have that backwards. Only aldehydes react with the Tollens reagent.
  7. Apr 10, 2007 #6


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    What is name of the product of cyanide reacting with a ketone?

    The last question only distinguishes the aldehydes from the ketones. All will react with 2,4-DNP but only an aldehyde(s) can react with the Tollen's reagent. Obviously there are two isomers of aldehydes with the empirical formula C4H8O. Can you draw the two isomers?
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