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The role of Water in... Watch

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    What is the role of water in:

    a) 2-chloro-2-methylpropane reacted with ethanol/water to give 2-methyl porpan-2-ol

    b) 2-chloro-2-methylpropane reacted with ethanol/water to give 2 methyl propene


    If you can hint me towards it it would be great
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    Are you sure those reactions are correct?
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    (Original post by illusionz)
    Are you sure those reactions are correct?
    ...They are now... The first reaction was wrong it created an alcohol... It's from the June 2009 U2 paper...Q. 20 Section B
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    Chlorine is a good leaving group, thus it just depends whether another group substitutes for it, or whether it's oxidised. Is the difference heat?
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    (Original post by Booyah)
    What is the role of water in:

    a) 2-chloro-2-methylpropane reacted with ethanol/water to give 2-methyl porpan-2-ol

    b) 2-chloro-2-methylpropane reacted with ethanol/water to give 2 methyl propene


    If you can hint me towards it it would be great
    Well the answers are a) nucleophile and b) base.

    I'm a bit dubious that the second reaction would actually work to any decent yield though... Are you sure it's not hydroxide instead of water?
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    (Original post by illusionz)
    Well the answers are a) nucleophile and b) base.

    I'm a bit dubious that the second reaction would actually work to any decent yield though... Are you sure it's not hydroxide instead of water?
    I think it's the type of question that goes for the ''elimination and substitution of haloalkanes compete with one another, Jonny found two products from the reaction of halokane A with conditions B...'' type route.
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    (Original post by illusionz)
    Well the answers are a) nucleophile and b) base.

    I'm a bit dubious that the second reaction would actually work to any decent yield though... Are you sure it's not hydroxide instead of water?

    Yeh it is a mixture of alcohol/Water heated at 65C .... I am not to sure what you mean by nucleophile and base... I understand that nucleophile is a highly electronegative species being attracted to a positive species but how does the 2- chloro 2-methylpropane become positively charged and what on Earth do you mean by Base?
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    (Original post by Booyah)
    Yeh it is a mixture of alcohol/Water heated at 65C .... I am not to sure what you mean by nucleophile and base... I understand that nucleophile is a highly electronegative species being attracted to a positive species but how does the 2- chloro 2-methylpropane become positively charged and what on Earth do you mean by Base?
    Positively charged because with an electronegative atom attached to a carbon, it steals more of the electrons, give the carbon a delta positive charge.

    Bases look to steal hydrogens
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    (Original post by That Bearded Man)
    Positively charged because with an electronegative atom attached to a carbon, it steals more of the electrons, give the carbon a delta positive charge.

    Bases look to steal hydrogens

    So because it is more electronegative does it get booted off via the OH group via rear end attack of something along those lines?
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    (Original post by Booyah)
    So because it is more electronegative does it get booted off via the OH group via rear end attack of something along those lines?
    Chlorine is a good leaving group, the carbon is delta positive, meaning it can be targeted by nucleophiles, the water molecule attacks the carbon, simultaneously kicking off the chlorine. Water then loses a H, which bonds with the Cl to form HCl. It is strange to see this reaction without a strong base such as NaOH.

    Might want to get another opinion on this but I think that's it.
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    (Original post by Booyah)
    So because it is more electronegative does it get booted off via the OH group via rear end attack of something along those lines?

    (Original post by That Bearded Man)
    Chlorine is a good leaving group, the carbon is delta positive, meaning it can be targeted by nucleophiles, the water molecule attacks the carbon, simultaneously kicking off the chlorine. Water then loses a H, which bonds with the Cl to form HCl. It is strange to see this reaction without a strong base such as NaOH.

    Might want to get another opinion on this but I think that's it.
    Because this is a tertiary haloalkane, the chlorine leaves forming Cl- and a tertiary carbocation which is then attacked by water, with loss of a proton forming the product. Tertiary haloalkanes are too bulky for the water to attack behind the chlorine.
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    (Original post by illusionz)
    Because this is a tertiary haloalkane, the chlorine leaves forming Cl- and a tertiary carbocation which is then attacked by water, with loss of a proton forming the product. Tertiary haloalkanes are too bulky for the water to attack behind the chlorine.
    That's right, my mistake, it's Sn1 not Sn2
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    (Original post by That Bearded Man)
    That's right, my mistake, it's Sn1 not Sn2
    Just for interests sake, that's one of the reasons why the reaction works fine with water in this case. Usually you'd use hydroxide ions as they're much better nucleophiles/bases, but as the rate determining step is loss of chloride and the carbocation is significantly more reactive than the starting alkyl halide so the quality of the nucleophile/base doesn't really matter.
 
 
 
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