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    Alkenes- Addition reaction of alkenes - Topic 9.

    Electrophile - Electron pair acceptor.

    Addition - Two molecules reacting to make one.

    Examples of electrophiles are: Br2, HBr, H2SO4

    These are the three we need to know, I'll basically do the conditions, equations (with ethene as an example) + comments for them in the next post.
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    (Original post by Anon_98)
    Alkenes- Addition reaction of alkenes - Topic 9.

    Electrophile - Electron pair acceptor.

    Addition - Two molecules reacting to make one.

    Examples of electrophiles are: Br2, HBr, H2SO4

    These are the three we need to know, I'll basically do the conditions, equations (with ethene as an example) + comments for them in the next post.
    Still reading, keep it up! :rave:
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    Okay, so we'll start with Br2.

    Reagent: Br2 gas

    Conditions: Room temperature.

    Equation with ethene: H2C=CH2 + Br2 --------> CH2BrCH2Br (I,2-dibromoethane)

    Comment:Bromine water is decolourised by alkenes.


    ~

    Okay now we'll move onto HBr

    Reagent: HBr

    Conditions: Room temperature.

    Equation with ethene: H2C=CH2 + HBr --------> CH3CH2Br (I-bromoethane)

    Comment:Colourless -> Colourless

    ~

    Finally, we have H2SO4

    Reagent: H2SO4

    Conditions: Cold, concentrated.

    Equation with ethene: H2C=CH2 + H2SO4 --------> CH3CH2OSO3H (ethylhydrogensulphate)

    Comment:The product is hydrolysed by warming in dilute sulphuric acid to produce ethanol.
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    Alkenes- Addition reaction of alkenes - Topic 9.

    Okay so now we're going to do the mechanisms for electrophillic addition in symmetrical alkenes(ONE PRODUCT.)

    Going to start with Hydrogen Bromide with ethene.. I'll attach the mechanism below as before:
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    Electrophillic addition reaction for HBr with ethene.

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    Okay, now I'm going to draw Bromine with ethene.

    You need to remember the following information about this reaction:

    Br2 is non polar and has no permanent dipole, itbecomes polarised as it approaches the region of high electron density in the C=C double bond. I.E. Induced polarisation occurs.
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    Electrophillic addition reaction for Br2 with ethene.

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    Finally, the mechanism for Sulphuric acid with ethene.
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    Electrophillic addition reaction for H2SO4 with ethene.

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    Alkenes- Addition reaction of alkenes - Topic 9.

    Alright, so now we're going to do the mechanism for an electrophillic addition to unsymmetrical alkenes (TWO PRODUCTS.)

    The example I'll be drawing is the two possible mechanisms for HBr and propene.
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    Okay, so the first picture formed a product of 1-bromopropane which is a MINOR product and the carbocation was a primary one.

    In the second picture, we have a product of 2-bromopropane which is a MAJOR product and the carbocation was a secondary one.

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    There are three types of carbocation with the following structures:

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    Alkenes- Addition reaction of alkenes - Topic 9.

    The order of stability of carbocations is:

    3° > 2° > 1°

    Rule: The more stable the carbocation, the more likely it is to be formed.


    Explain why 2-bromopropane is the major product in the reaction I just did above between propene and HBr?

    It is bc a secondary carbocation is more stable than a primary carbocation and is therefore formed in preference.
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    Alkenes- Addition reaction of alkenes - Topic 9.

    Alcohol production - industry (Hydration reaction)

    Reagent: H2O

    Conditions: Concentrated phosphoric acid catalyst, high temperature (300C), high pressure (6.5MPa)

    Equation with ethene: H2C=CH2 + H2O --------> CH3CH2OH
    Comment: Industrial method for making ethanol.


    ~


    Alkenes- Polymerisation of alkenes - Topic 9.

    Addition polymerisation
    Reagent: -

    Conditions: Organic peroxide indicator or other catalyst.

    Equation with ethene: It's basically one of those repeating unit thingies, which I cba to draw bc.. simple enough.
    Comment: Two forms are made: LDPE and HDPE. Poly(alkenes) are unreactive therefore not biodegradable.

    Uses of poly(ethene): Washing up bowls, plastic bags.

    Uses and recycling of poly(propene): Rope, carpets: recycled by melting in absence of air.
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    Quick test question for you guys: from the following molecules tell me the most electronegative to the least electronegative and why you chose in that order:

    1) CH3CH(BR)CH2COOH
    2) CH3CH2CH(BR)COOH
    3)CH2(BR)CH2CH2COOH
    4)CH3CH2CH2COOH
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    Blah, it's not letting me space things out without going all funny so the thingy I've just posted above has a really weird format which is quite annoying to look at. >.>

    Anyway..

    Alcohols- Nomenclature - Topic 10.

    Okay, um - I think I can skip this bc you pretty much get all the practice from naming compounds when doing past papers + you can't really make notes on it etc.
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    Alcohols- Ethanol production- Topic 10.

    C6H12O6(aq) -------------------------> 2CH3CH2OH(aq) + 2CO2(g)

    Type of reaction: Fermentation.

    Conditions: Aqueous, yeast (enzyme- zymase), 37C, anaerobic.

    If the temperature is too high then enzymes will denature, if the temperature is too low then the reaction will also be too slow.

    ~

    Advantages and disadvantages of fermentation over hydration.

    So, advantages:

    - Glucose is a renewable resource.

    - Less energy is required.

    - Cheap equipment - low level technology.


    Disadvantages:

    - Lower yield and purity (15% vs 95%)

    - Lower rate.. (days vs seconds)

    - Batch process (vs continuous) - Manpower more expensive.
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    Alcohols- Ethanol production- Topic 10.

    Biofuel - A fuel which is derived from renewable biological sources.

    By law, petrol sold in the UK has 5-10% ethanol added to it.

    'Carbon neutral' - A process that releases no net CO2 into the atmosphere + thus does not contribute to the greenhouse effect.


    Extent to which fermentation can be considered as carbon neutral
    Well, fermentation releases the same amount of CO2 as was originally absorbed by the plants..

    HOWEVER,

    Other energy costs in the production of the crops + the industrial process may not be carbon neutral.
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    Alcohols- Classification + reactions - Topic 10.

    Alright so, alcohols can be classified as tertiary, secondary + primary- I'll attach a drawing.
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