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    Which one has a higher electron density?
    Benzene or cyclohexene?
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    (Original post by Varsh05)
    Which one has a higher electron density?
    Benzene or cyclohexene?
    Cyclohexene, hence it being able to polarise bromine
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    (Original post by otrivine)
    Why alcohol have short retention time and why alkane would have long retention time?
    Because the alcohol would be less soluble in the alkane stationary phase cuz it forms hydrogen bonds. The alkane, which can form dipolar bonds with the alkane stationary phase will be more soluble so will take longer to reach the detector.
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    (Original post by Varsh05)
    Which one has a higher electron density?
    Benzene or cyclohexene?
    Benzene has delocalised electrons so they are spread between all the carbon atoms in the ring - they are not concentrated in one place.

    Cyclohexene has electrons localised between two carbon atoms - there is a region of high electron density above and below the plane due to the pi bond.
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    (Original post by _HabibaH_)
    Because the alcohol would be less soluble in the alkane stationary phase cuz it forms hydrogen bonds. The alkane, which can form dipolar bonds with the alkane stationary phase will be more soluble so will take longer to reach the detector.
    alkane stationary phase? huuuuuuuh?
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    (Original post by Mus1995)
    This explains my question about 4(b) in June 2012. Attachment 227648


    Posted from TSR Mobile
    Just did that paper, got 50 which is not as good as I hoped. That stupid benzaldehyde was annoying but I completely messed up on 3ciii where you had to give the two stage synthesis, I did it backwords as I thought it was compound C from oxandrolone.

    Posted from TSR Mobile
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    (Original post by Georgiina_Tee)
    I've been looking for an hour and 21 minutes now, looked for like the first 20 pages and from the back to the last 10 can you link me please maybe its because I'm on my phone :'(

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    I'm on my phone too so I can't link it.

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    (Original post by Sarangtaec)
    There are LOADS so forgive me if I miss any.

    Nitration of Benzene: C6H6 + Concentrated HNO3 ==> C6H5NO2 + H+
    Conditions: Reflux + Concentrated H2SO4 Catalyst
    Formation of electrophile: H2SO4 + HNO3 ==> HSO4- + NO2+ = H2O
    How the catalyst works: H+ = HSO4- ==> H2SO4
    Halogenation of Benzene: C6H6 + Cl2/Br2 ==> C6H5Cl/C6H5Br + HCl/HBr
    Conditions: AlCl3/AlBr3 Catalyst
    Reduction of Nitrobenzene: C6H5NO2 + Sn/Conc. HCl (6[H]) ==> C6H5NH2 + 2H2O
    Conditions: Reflux
    Diazotisation: C6H5NH2 + Concentrated HCl + Concentrated HNO2 ==> C6H5N2+Cl- + H2O
    Conditions: Under 10 degrees celcius
    Coupling: C6H5N2+Cl- + Phenol ==> Azo Dye
    Conditions: Alkaline conditions, under 10 degrees celcius

    Test for Carbonyls: Add 2,4-DNPH forms orange precipitation which is addition-elimination reaction
    Identifying carbonyl: Filter and recrystallise the precipitate and measure melting point, compare against known values.
    Distinguishing Aldehyde or Ketone: Add Tollen's reagent which forms a silver mirror if aldehyde is present.
    Reducing aldehydes/ketones: Add NaBH4 which is Nucleophilic addition reaction

    Formation of polyester: Carboxylic acid + alcohol monomers
    Formation of polyamide: Carboxylic acid + amine monomers

    Primary Alcohol + [O] ==> Aldehyde (Distillation)
    Primary Alcohol + 2[O] ==> Carboxylic acid (Reflux)
    Secondary Alcohol + [O] ==> Ketone (Reflux)

    Halogenation of alkenes: Add HCl/HBr??
    Test for Alkenes: Add Br2 ==> Colour changes from orange to colourless
    Test for Phenol (or any OH group): Add Na ==> Effervescent produced as Hydrogen released
    Phenol + Br2 ==> 2,4,6-tribromophenol (white precipitate)

    Fatty acid + Glycerol ==> Triglyceride

    Acid Hydrolysis: Add H2O with presence of acid catalyst under reflux
    Alkaline Hydrolysis: Add NaOH in alkaline conditions

    My brain's gone blank haha maybe others could add? Hope this helps, sorry if I made any mistakes.
    Thank you soo much it really is a big help
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    (Original post by _HabibaH_)
    Yep. The molecular formula is C14H10O4 so divide all of that by 2 (because you can) and you end up with the empirical fornula being C7H5O2.
    thank you! good luck with f324!
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    (Original post by kevloui)
    Cyclohexene, hence it being able to polarise bromine
    So when you're comparing the two,you'd say bromine has a low electron density whilst cyclohexene has a higher electron density,which is why it polarises bromine?
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    (Original post by _HabibaH_)
    Benzene has delocalised electrons so they are spread between all the carbon atoms in the ring - they are not concentrated in one place.

    Cyclohexene has electrons localised between two carbon atoms - there is a region of high electron density above and below the plane due to the pi bond.
    Thanks!
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    (Original post by Varsh05)
    So when you're comparing the two,you'd say bromine has a low electron density whilst cyclohexene has a higher electron density,which is why it polarises bromine?
    Whilst that is correct, I have never seen a mark scheme say that you need to write that bromine has a low electron density.
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    (Original post by kevloui)
    Whilst that is correct, I have never seen a mark scheme say that you need to write that bromine has a low electron density.
    Ok..thanks anyway
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    (Original post by kevloui)
    alkane stationary phase? huuuuuuuh?
    Yes in GC sometimes there is an alkane stationary phase. So the method of seperation is solubility.

    Check Jan 2012. So they basically asked in that paper why alkanes, esters and alcohols would have different retention times in an ALKANE stationary phase. Answer was something to do with alkane dissolving more, esters and alcohols being less soluble because of their hydrogen bonding.
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    (Original post by zainn)
    thank you! good luck with f324!
    Same, you too. If you have any other bits you find hard-ish, please post on here. We'll all benefit form each others questions.
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    (Original post by _HabibaH_)
    Yes in GC sometimes there is an alkane stationary phase. So the method of seperation is solubility.

    Check Jan 2012. So they basically asked in that paper why alkanes, esters and alcohols would have different retention times in an ALKANE stationary phase. Answer was something to do with alkane dissolving more, esters and alcohols being less soluble because of their hydrogen bonding.
    Yea that's right, but that's situational. I mean, otrivine never actually stated what the stationary phase was, she just said which one would have a longer retention time, that's why I was surprised you assumed it was an alkane. I think its safe to assume that they're water based (if we're not told otherwise).
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    (Original post by kevloui)
    Yea that's right, but that's situational. I mean, otrivine never actually stated what the stationary phase was, she just said which one would have a longer retention time, that's why I was surprised you assumed it was an alkane. I think its safe to assume that they're water based.
    Lol, yep it is situational. I basically assumed because of the past paper question (which I still remember). In the real exam, however, assumptions are not a good luck so I need to fix up.
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    (Original post by Georgiina_Tee)
    Who has Jan 13 paper or link to someone who has posted I can only find the ms

    Posted from TSR Mobile
    http://www.thestudentroom.co.uk/show...4#post43167740

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    (Original post by Varsh05)
    So when you're comparing the two,you'd say bromine has a low electron density whilst cyclohexene has a higher electron density,which is why it polarises bromine?
    Benzene has a lower electron density that cyclohexene. That's all you need to know.

    Cyclohexene can polarise a Br2 molecule better than benzene can, hence there is no need for a halogen carrier.
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    (Original post by _HabibaH_)
    Lol, yep it is situational. I basically assumed because of the past paper question (which I still remember). In the real exam, however, assumptions are not a good luck so I need to fix up.
    lol yea assumptions can go either way in these exams.
 
 
 
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