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A2 Chemistry (Unit 4) - Questions arising from revision! watch

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    Hi everyone, I will be grateful to anyone who can help me with any of the following questions! Unanswered queries cloud my mind :eek3: I'm really not being lazy but I've got 3 textbooks and can't find these out.

    Seriously though I am really grateful for any help.


    1) CH3CH(OH)CH2NH2 ......is that 1-aminopropanol or 2-hydroxypropylamine? Or doesn't it matter?
    Answered.

    2) For reduction of carbonyl group C=O, we can use NaBH4 aqueous followed by dil. H2SO4. Is that correct? One textbook seems to think it should be NaBH4 in ethanol?


    3) Does benzene discolour bromine water (i.e. test for double bonds)?
    Answered.

    4) How do you get nucleophilic substitution of chlorine or bromine into benzene?
    Answered.

    5) C6H5N ----> C6H5COOH
    How does this happen? :confused:


    6) Is Sn just a catalyst in the reduction of nitriles or does it actually react with the HCl?
    Answered.
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    (Original post by seeker1)
    Hi everyone, I will be grateful to anyone who can help me with any of the following questions! Unanswered queries cloud my mind :eek3: I'm really not being lazy but I've got 3 textbooks and can't find these out.

    Seriously though I am really grateful for any help.


    1) CH3CH(OH)CH2NH2 ......is that 1-aminopropanol or 2-hydroxypropylamine? Or doesn't it matter?
    I would go for aminopropan-2-ol.. but I'm not a chemist..

    2) For reduction of carbonyl group C=O, we can use NaBH4 aqueous followed by dil. H2SO4. Is that correct? One textbook seems to think it should be NaBH4 in ethanol?
    cant remember

    3) Does benzene discolour bromine water (i.e. test for double bonds)?
    no - the delocalized pi systems stablise benzine so that it deos not readily undergo electrophilic substitution

    4) How do you get nucleophilic substitution of chlorine or bromine into benzene?
    Use a halogen carrier




    6) Is Sn just a catalyst in the reduction of nitriles or does it actually react with the HCl?
    It's just a catalyst
    gotta worn you, it's been a long time...
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    A halogen carrier? But a Br- or Cl- ion wouldn't work for electrophilic substitution... would it attack nucleophilically (is that a word lol) on a delta positive C atom? I'm just trying to think how it would work.
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    have a free (and bloody good) chemistry site - I used it lots at A2 www.chemguide.co.uk
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    (Original post by seeker1)
    A halogen carrier? But a Br- or Cl- ion wouldn't work for electrophilic substitution... would it attack nucleophilically (is that a word lol) on a delta positive C atom? I'm just trying to think how it would work.
    http://www.chemguide.co.uk/mechanism...ation.html#top
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    (Original post by seeker1)
    1) CH3CH(OH)CH2NH2 ......is that 1-aminopropanol or 2-hydroxypropylamine? Or doesn't it matter?
    The general 'rule' is that the most oxidised group takes priority. That would make it:

    1-aminopropan-2-ol

    2) For reduction of carbonyl group C=O, we can use NaBH4 aqueous followed by dil. H2SO4. Is that correct? One textbook seems to think it should be NaBH4 in ethanol?
    The sulphuric acid is just used for the 'work up' - it is not part of the reduction reaction.

    3) Does benzene discolour bromine water (i.e. test for double bonds)?
    No

    4) How do you get nucleophilic substitution of chlorine or bromine into benzene?
    Benzene undergoes electrophilic substitution using an AlCl3/Cl2 (Freidel Crafts catalyst system)

    The chlorine molecule 'bonds' to the electron deficient aluminium trichloride:
    Cl---Cl--->AlCl3
    weakening the Cl-Cl bond and polarising it:

    (d+)Cl---Cl--->AlCl3

    The partially positive chlorine can then be attacked by the benzene delocalised electrons.

    5) C6H5N ----> C6H5COOH
    How does this happen? :confused:
    Your first molecule does not exist!



    6) Is Sn just a catalyst in the reduction of nitriles or does it actually react with the HCl?
    No it is not a catalyst.
    The Sn reacts with HCl producing hydrogen gas which acts as the reductant. The product is an intermediate tin complex which must then be decomposed by the addition of dilute base to release the amine.

    Tin cannot be recovered chemically unchanged, so it cannot be a catalyst.
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    I have atm no motivation to revise for the upcoming Unit 4, mainly because I have three exams before it.
    But I'm generally comfortable with Unit 4, if any chapter I'm still if'fy about it's Chapter 11 of the AQA spec. Don't like mass IR spectrum and that..:rolleyes:

    Btw good luck with your studies.
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    First off, a huge thank you.

    (Original post by charco)
    (Original post by seeker1)
    5) C6H5N ----> C6H5COOH
    How does this happen? :confused:
    Your first molecule does not exist!
    My bad!

    C6H5CN ------> C6H5COOH
    I don't know how you would remove the N atom :|


    (btw I don't think this is on the syllabus but I still do appreciate your help so much - knowledge for the sake of knowledge as they say!)
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    (Original post by seeker1)
    First off, a huge thank you.



    My bad!

    C6H5CN ------> C6H5COOH
    I don't know how you would remove the N atom :|


    (btw I don't think this is on the syllabus but I still do appreciate your help so much - knowledge for the sake of knowledge as they say!)
    It's very easy, you just warm the compound up with dilute acid:

    C6H5CN + H2O --> C6H5CONH2

    C6H5CONH2 + H2O + H+ --> C6H5COOH + NH4+
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    my bad on the tin front.. but I'm sure I was taught it was a catalyst.. - ow well my chemistry days are long gone
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    (Original post by seeker1)
    Hi everyone, I will be grateful to anyone who can help me with any of the following questions! Unanswered queries cloud my mind :eek3: I'm really not being lazy but I've got 3 textbooks and can't find these out.

    Seriously though I am really grateful for any help.


    1) CH3CH(OH)CH2NH2 ......is that 1-aminopropanol or 2-hydroxypropylamine? Or doesn't it matter?
    Answered.

    2) For reduction of carbonyl group C=O, we can use NaBH4 aqueous followed by dil. H2SO4. Is that correct? One textbook seems to think it should be NaBH4 in ethanol?


    3) Does benzene discolour bromine water (i.e. test for double bonds)?
    Answered.

    4) How do you get nucleophilic substitution of chlorine or bromine into benzene?
    Answered.

    5) C6H5N ----> C6H5COOH
    How does this happen? :confused:


    6) Is Sn just a catalyst in the reduction of nitriles or does it actually react with the HCl?
    Answered.

    You mean C6H5CN its a hydrolysis reaction using water acidified with dil HCL.

    You can use a wide range of reagents, because you want a H+ ion, you can even use methanol with water :yes: .
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    (Original post by seeker1)

    2) For reduction of carbonyl group C=O, we can use NaBH4 aqueous followed by dil. H2SO4. Is that correct? One textbook seems to think it should be NaBH4 in ethanol?
    I was told it was NaBH4 and H20 :/.
 
 
 
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