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    (Original post by rory58824)
    Is this off-topic?

    Attachment 545797
    No mate, it was perfect


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    (Original post by thad33)
    No mate, it was perfect


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    Brilliant, maybe the cat can give us hope for the exams
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    Can anyone tell me exactly what they mean by this part of the spec:

    "Compare the Kekulé and delocalised model of benzene in terms of p-orbital overlap forming pi bonds"

    I know for delocalised model you would say: Sideways overlap of the p-orbital produces a delocalised pi-electron ring above and below the plane. But what about Kekulé's, how would you word that?
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    (Original post by RayMasterio)
    <a href="http://tinypic.com?ref=mcbrtj" target="_blank"><img src="http://i65.tinypic.com/mcbrtj.png" border="0" alt="Image and video hosting by TinyPic"></a>

    can someone please tell me why the reduction process is wrong? Is a reduction of a COOH always OH? Or is it because we are polymerising so it must be COOH + OH to form the peptide link?
    You cannot reduce carboxylic acid with NaBH4 as it is not strong enough, LiAlH4 is used , and it is a different mechanism (which is not on ocr spec), therefore mechanism you have drawn is not correct and you should just remember if they ask to reduce carboxylic acid it turns into a primary alcohol
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    Can someone explain this? This molecule only has 4 hydrogen environment but 5 peaks??

    You cannot see the splitting pattern on the sheet so I've written up the splitting next to the peak
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    Guys, in NMR questions when they say ''this proton was initially expected at x ppm but is at y ppm instead'' which chemical shift should we analyse? ;S
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    (Original post by AndrewC19)
    Can anyone tell me exactly what they mean by this part of the spec:

    "Compare the Kekulé and delocalised model of benzene in terms of p-orbital overlap forming pi bonds"

    I know for delocalised model you would say: Sideways overlap of the p-orbital produces a delocalised pi-electron ring above and below the plane. But what about Kekulé's, how would you word that?
    Kekules model of carbon bonds different lengths until x ray crystallography reveal that they're all the same

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    (Original post by AqsaMx)
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    Can someone explain this? This molecule only has 4 hydrogen environment but 5 peaks??

    You cannot see the splitting pattern on the sheet so I've written up the splitting next to the peak
    Are you sure you have the correct molecule?
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    (Original post by AndrewC19)
    Can anyone tell me exactly what they mean by this part of the spec:

    "Compare the Kekulé and delocalised model of benzene in terms of p-orbital overlap forming pi bonds"

    I know for delocalised model you would say: Sideways overlap of the p-orbital produces a delocalised pi-electron ring above and below the plane. But what about Kekulé's, how would you word that?
    Kekulé's model consists of p-orbitals that overlap between 2 carbons, meaning that the electrons are 'localised' between 2 carbons and not delocalised in the ring.
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    (Original post by alow)
    How exactly was that aggressive? Calm down dear.

    There are more resources than just past papers.
    Just kidding pal!

    Set me these resources tho
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    (Original post by rory58824)
    Is this off-topic?

    Attachment 545797
    I got my ION you
    *slaps knee*
    ok i'll leave..
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    (Original post by RetroSpectro)
    Are you sure you have the correct molecule?
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    (Original post by AqsaMx)
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    Not sure how thats possible, there must be an error some where, whether it be with the question or your interpretation :dontknow:
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    (Original post by Heisenberg___)
    Came across this fantastic link for old chemistry past papers. The person who made this has also kindly highlighted questions that we can skip (as they aren't relevant to our spec). Enjoy!

    http://www.chemhume.co.uk/A2CHEM/Exa...additional.htm
    This is great! Thanks!
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    (Original post by ToLiveInADream)
    Guys, in NMR questions when they say ''this proton was initially expected at x ppm but is at y ppm instead'' which chemical shift should we analyse? ;S
    The chemical shift at x ppm. I think they do this so that the peaks don't overlap, making it hard to analyse
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    (Original post by Kamara7)
    The chemical shift at x ppm. I think they do this so that the peaks don't overlap, making it hard to analyse
    Ahh that makes sense! I'll practise some of these questions now, thanks
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    Guys, another question:

    I don't understand the initiative behind these kind of mechanisms - which is probably why I get them wrong. I would be grateful if someone could explain intuitively what's happening.

    Why does the electron pair move to the Carbon atom, from the oxygen? Why not from the o-c bond to the oxygen atom that is removed?
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    And also this question. The answer isn't making sense. When D20 is added, do we assume the OH is substituted by a H? And I understand there are two environments (if we sub OH with H) but what would the splitting be? The CH would be symmetrical? so would it be a triplet: triplet (so there is two adjacent CH2's)?
    Is this environment R-CH or is it HCCO?
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    (Original post by RayMasterio)



    And also this question. The answer isn't making sense. When D20 is added, do we assume the OH is substituted by a H? And I understand there are two environments (if we sub OH with H) but what would the splitting be? The CH would be symmetrical? so would it be a triplet: triplet (so there is two adjacent CH2's)?
    Is this environment R-CH or is it HCCO?
    Adding D2O does not replace -OH groups with H atoms. All it does it cause the H in the -OH to be replaced with D (an isotope of H), which stops these groups from producing any peak. So the spectrum after D2O has been added is the same as before, except the singlet caused by the -OH has now gone.
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    (Original post by RetroSpectro)
    Not sure how thats possible, there must be an error some where, whether it be with the question or your interpretation :dontknow:
 
 
 
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