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    Hi, just come across a few questions (might be old spec...) asking for the reaction of hydrogen cyanide with ketones, asking for the mechanism. It's not on the spec but wasn't sure if it could just be an applying knowledge question? Has anyone else come across this sort of thing?
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    (Original post by _HabibaH_)
    Q. Write out the equation of Phenol with H2SO4 and then with H2O.
    Does phenol react with H2SO4? I don't think it does. Whats your answer to this?
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    (Original post by sidmanny)
    Hi, just come across a few questions (might be old spec...) asking for the reaction of hydrogen cyanide with ketones, asking for the mechanism. It's not on the spec but wasn't sure if it could just be an applying knowledge question? Has anyone else come across this sort of thing?
    Post the paper and question number so i can have a look at it.
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    hows everyone feeling for this exam?
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    (Original post by thers)
    1) I would draw it but can't on the computer so is it a benzene ring with an NH3+ Cl - sticking out?

    2)Don't really know but will say C=O bond is broken on exposure to light weakening its structure - hence making it elastic.

    3) Enthalpy change of hydrogenation of benzene is less exo than expected so supports the evidence for delocalised pi bond in benzene.

    4) Not sure but. propylamine because in 3-methylphenylamine lone pair of electrons on N are partially delocalised into ring so are less able to donate these to H+ in acidic conditions to form a dative covalent bond?
    2) Elastic because the Hydrogen bonds can break and reform.

    4) Comparison to aliphatic: Aliphatic has the electrons more strongly attracted to N(delta-negative) rather than C(delta-positive) due to electronegative. also, something to do with an inductive force allowing the electrons to be donated to the H+ more readily.

    Apart from that, tis all right!
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    (Original post by thers)
    Does phenol react with H2SO4? I don't think it does. Whats your answer to this?
    Phenol is a weak acid and Sulfuric Acid is a strong acid. It kind of intercalated with F325 in the sense that Phenol acts as a base with Sulfuric Acid but as an acid with Water.

    So... (the arrows are supposed to be the equilibrium ones, I think)

    H2SO4 + C6H5OH ----> HSO4- + C6H5OH2+

    H2O + C6H5OH ----> H3O+ + C6H5O-
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    (Original post by sidmanny)
    Hi, just come across a few questions (might be old spec...) asking for the reaction of hydrogen cyanide with ketones, asking for the mechanism. It's not on the spec but wasn't sure if it could just be an applying knowledge question? Has anyone else come across this sort of thing?
    Yep, its an application one if it comes in the new spec questions.

    Basically, the H- reacts with the Ketone in the same way as the CN-.
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    (Original post by _HabibaH_)
    1) What is the intermediate amine salt formed in the Reduction of Nitrobenzene reaction? (1)

    2) What property makes Terylene (a polyester) elastic? (1)

    3) What is the difference between the enthalpy change of Benzene and Kekule's structure a result of? (2)

    4) Which is more basic - propylamine or 3-methylphenylamine? Explain. (3/4)
    1) NH4+ CL-

    2) high tensile strength, forces between molecules, ester linkage formation, because it contains C=O so is strong and also there are weak forces C-C and they allow a degree of elasticity

    3) enthalpy change of benzene is less exothermic than the expected value , this is because the Kekule structure consists of the double bond, so when hydrogen is added the double bond breaks and hydrogen bond to the carbon atom, and hence the breaking of the double bond in the kekule is the result of it being more exothermic, the hydrogenation of kekule

    4) propylamine, this is because the electrons in the 3-phenylamine is delcoalised into the ring, and hence, the electrons are used for the bonding of the amine with the benzene ring by electrophilic substitution, nitrogen forms a covalent bond with the intermediate
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    (Original post by thers)
    Post the paper and question number so i can have a look at it.
    It's not from a paper, just a pack of past questions I got from school. This is one of the questions...

    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


    There's another unfamiliar one:
    Propanone reacts with I2 and NaOH, giving two products, A and B.
    Give the structural formula of A and B.
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    (Original post by otrivine)
    1) NH4+ CL-

    2) high tensile strength, forces between molecules, ester linkage formation, because it contains C=O so is strong and also there are weak forces C-C and they allow a degree of elasticity

    3) enthalpy change of benzene is less exothermic than the expected value , this is because the Kekule structure consists of the double bond, so when hydrogen is added the double bond breaks and hydrogen bond to the carbon atom, and hence the breaking of the double bond in the kekule is the result of it being more exothermic, the hydrogenation of kekule

    4) propylamine, this is because the electrons in the 3-phenylamine is delcoalised into the ring, and hence, the electrons are used for the bonding of the amine with the benzene ring by electrophilic substitution, nitrogen forms a covalent bond with the intermediate
    1) we don't start with NH3 so NH4+Cl- cannot be formed. We start with the Phenylamine so NH2 which reacts with HCl forming NH3+Cl-.

    2)) Elasticity is down to the breaking and reforming of hydrogen bonds but the others are properties of Terylene, just not in relation to this by the sound of it.

    3) the question was the difference between the enthalpy changes so asking for the reason behind the delocalisation/resonance energy - the answer is the delocalised electron system providing greater stability.

    4) The simple comparison is that...
    - Phenylamine's lone pair of e- off the N are delocalised in the benzene ring
    - The Propylamine electronegativity ensures that the N(delta-negative) attracts the electrons more strongly compared to the C(delta-positive)
    - The inductive force enables the e- to be donated more readily to the H+ in the Propylamine
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    (Original post by _HabibaH_)
    1) we don't start with NH3 so NH4+Cl- cannot be formed. We start with the Phenylamine so NH2 which reacts with HCl forming NH3+Cl-.

    2)) Elasticity is down to the breaking and reforming of hydrogen bonds but the others are properties of Terylene, just not in relation to this by the sound of it.

    3) the question was the difference between the enthalpy changes so asking for the reason behind the delocalisation/resonance energy - the answer is the delocalised electron system providing greater stability.

    4) The simple comparison is that...
    - Phenylamine's lone pair of e- off the N are delocalised in the benzene ring
    - The Propylamine electronegativity ensures that the N(delta-negative) attracts the electrons more strongly compared to the C(delta-positive)
    - The inductive force enables the e- to be donated more readily to the H+ in the Propylamine
    I dont agree with the 3rd point your question was talking about kekule and benzene
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    Is this a morning or an afternoon exam? Also, it's on Wednesday right? I lost my diary
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    (Original post by otrivine)
    I dont agree with the 3rd point your question was talking about kekule and benzene
    I don't understand.

    I was asking why there was a difference in the enthalpy change between benzene and Kekule's structure.

    Which quite simply is that because Benzene has delocalised electrons (as opposed to the localised electrons between the pi bonds in Kekule's structure), the energy needed to hydrogenate it will be less exothermic/more endothermic/higher because it is more stable. This difference in energy is known as the resonance energy/delocalisation energy.
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    (Original post by _HabibaH_)
    I don't understand.

    I was asking why there was a difference in the enthalpy change between benzene and Kekule's structure.

    Which quite simply is that because Benzene has delocalised electrons (as opposed to the localised electrons between the pi bonds in Kekule's structure), the energy needed to hydrogenate it will be less exothermic/more endothermic/higher because it is more stable. This difference in energy is known as the resonance energy/delocalisation energy.
    It also has to do with the double bonds, as there are no double bonds in benzene and has double bonds in kekule so the pi bond has to be broken down in order for a bond to form between hydrogen and carbon
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    (Original post by otrivine)
    It also has to do with the double bonds, as there are no double bonds in benzene and has double bonds in kekule so the pi bond has to be broken down in order for a bond to form between hydrogen and carbon
    Yes. So the double bonds are easy to hydrogenate compared to Benzene? Because electrons are localised (region of high elec density) compared to delocalised in Benzene?

    Sorry if I sound like I'm playing this 'delocalised system' record over and over. It's just that's the basic reason in the book.
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    (Original post by _HabibaH_)
    Yes. So the double bonds are easy to hydrogenate compared to Benzene? Because electrons are localised (region of high elec density) compared to delocalised in Benzene?

    Sorry if I sound like I'm playing this 'delocalised system' record over and over. It's just that's the basic reason in the book.
    yes because the bonds in the C=C in kekule is localed and in the benzene the pi electrons are delocalised
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    (Original post by JackVM)
    Is this a morning or an afternoon exam? Also, it's on Wednesday right? I lost my diary
    Morning
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    (Original post by otrivine)
    yes because the bonds in the C=C in kekule is localed and in the benzene the pi electrons are delocalised
    Okidokes. Yep, sorry for the confusion.
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    (Original post by _HabibaH_)
    Okidokes. Yep, sorry for the confusion.
    No worries, its my fault a but, its just that my mind is focused on C4 as the exam is tomorrow so cant think a lot of chem today
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    (Original post by otrivine)
    No worries, its my fault a but, its just that my mind is focused on C4 as the exam is tomorrow so cant think a lot of chem today
    Aaah that's that comprehension one right? I hear it's a difficult one, good luck with it.

    Any more questions you have?
 
 
 
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