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    (Original post by alow)
    Do you know what a resonance form is?
    Ive drawn resonance structures for CO3 2- and benzene but havent fully understood them

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    (Original post by ayvaak)
    Ive drawn resonance structures for CO3 2- but i havent fully understood it

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    So, usually when we draw the structures of molecules the drawings do not perfectly represent electron density in the system (which is more accurately described by molecular orbital theory).

    Resonance forms help to suggest the electron density (and hence reactivity) of different sites in a molecule without the need for lots of calculations. For most molecules there are many resonance forms you can draw but you want to look out for forms which would be expecially stable, such as those with negative charges localised on oxygens as these will have more of their 'character' in the real molecule. When you draw the resonance form of something like nitrobenzene, the most stable resonance forms are those where you push an electron from the π system to the neutral oxygen of the nitro substituent. Using the Kekulé structure of benzene this gives postivie charges at the ortho and para postitions, and hence these positions will be less likely to donate electrons.
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    (Original post by alow)
    So, usually when we draw the structures of molecules the drawings do not perfectly represent electron density in the system (which is more accurately described by molecular orbital theory).

    Resonance forms help to suggest the electron density (and hence reactivity) of different sites in a molecule without the need for lots of calculations. For most molecules there are many resonance forms you can draw but you want to look out for forms which would be expecially stable, such as those with negative charges localised on oxygens as these will have more of their 'character' in the real molecule. When you draw the resonance form of something like nitrobenzene, the most stable resonance forms are those where you push an electron from the π system to the neutral oxygen of the nitro substituent. Using the Kekulé structure of benzene this gives postivie charges at the ortho and para postitions, and hence these positions will be less likely to donate electrons.

    So when they say its a better electrophile as electrons are withdrawn they're talking the functional group -NO2 being a better electrophile?
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    (Original post by ayvaak)
    So when they say its a better electrophile as electrons are withdrawn they're talking the functional group -NO2 ?
    Yes. Electrons are withdrawn from the π system by the nitro substituent.
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    (Original post by alow)
    Yes. Electrons are withdrawn from the π system by the nitro substituent.
    But how how does this allow for the polynitration of nitrobenzene?
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    (Original post by ayvaak)
    But how how does this allow for the polynitration of nitrobenzene?
    What is the mechanism for addition of nitro groups to an aromatic ring?
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    (Original post by alow)
    What is the mechanism for addition of nitro groups to an aromatic ring?

    electrophillic substitution

    But isnt there going to be delta+ in ortho and para positions on the benzene molecule thus making those areas less electrophilic as a result of the NO2 group becoming more electrophillic. Why would +NO2 substitute the Hydrogens in those positions?
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    (Original post by ayvaak)
    electrophillic substitution

    But isnt there going to be delta+ in ortho and para positions on the benzene molecule thus making those areas less electrophilic as a result of the NO2 group becoming more electrollic. Why would NO2 substitute the Hydrogens in those positions?
    So, you know ortho and para are less likely to have electrophillic substitution occur, which means... ?
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    (Original post by alow)
    So, you know ortho and para are less likely to have electrophillic substitution occur, which means... ?
    it adopts a meta position?
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    (Original post by ayvaak)
    it adopts a meta position?
    Exactly. The wiki page says the reaction produces a 93% meta product, which agrees with our predictions using resonance structures.
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    (Original post by alow)
    Exactly. The wiki page says the reaction produces a 93% meta product, which agrees with our predictions using resonance structures.

    Thank you for being patient with me
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    (Original post by ayvaak)
    Thank you for being patient with me
    No problem
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    (Original post by Jade Li)
    Are you guys in year 12 or 13? I'm in year 12
    My school doesn't really have an year 13 so Year 12 for us is basically both of those combined :P Does that make sense? o.O
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    (Original post by Manexopi)
    Anyone know any good resources for mass spec? (AQA A2)
    https://chemrevise.org/revision-guides/
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    (Original post by notsoclueless)
    My school doesn't really have an year 13 so Year 12 for us is basically both of those combined :P Does that make sense? o.O
    No.
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    (Original post by alow)
    No.
    Figured
    It did make sense in my head though :P
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    (Original post by ayvaak)
    Thank you for being patient with me
    Attached
    Attached Files
  1. File Type: ppt Directing effects.ppt (608.5 KB, 61 views)
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    Hey guys, wondering if anyone knows of any AQA past paper style questions (kind of like the solomon papers for maths). Running out of chem 4 papers and I'd like to attempt some different styles of questions. Or even just a collection of exam style questions etc. thank you!
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    (Original post by notsoclueless)
    Figured
    It did make sense in my head though :P
    I got a notif that you tagged me in something ?...
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    I was wondering could any of you recommend a method of studying chemistry as i have a mock exam coming up, im well aware of the traditional: Textbook ---> notes ---> exam practice

    but i was wondering were there any other methods you could recommend for example for GCSE a lot of people would recommend mygcsescience

    thanks in advance,
 
 
 
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