Hey there! Sign in to join this conversationNew here? Join for free

OCR AS - Chemistry Unit F322 - Chains, energy and resource - REVISION! watch

    Offline

    2
    ReputationRep:
    Someone explain please:

    E/Z isomerism as an example of
    stereoisomerism, in terms of restricted
    rotation about a double bond and the
    requirement for two different groups to be
    attached to each carbon atom of the C=C
    group,

    cis-trans isomerism as a special case of
    E/Z isomerism in which two of the
    substituent groups are the same.


    BUT E/Z and cis/trans are the same?
    thanks.
    Offline

    0
    ReputationRep:
    Basically, Cis isomerism is the same as z isomerism. The non hydrogen groups attached to the C=C are on the same size.

    Trans isomerism is E isomerism. The non hydrogen groups are on opposite sides of the C=C bond.
    Offline

    0
    ReputationRep:
    Not always!
    OK, to get stereoisomers, you have to have:

    1) a carbon-carbon double bond, as that restricts rotation and locks the groups in place
    2) each carbon in the C=C bond must have two different groups on it.

    To decide on whether it's E/Z, look at carbon 1 in the C=C bond, and decide which group has the highest priority (highest Mr). Now look at carbon 2 in the C=C bond and decide which group has the highest mass. If they are on the same side (Ze same side) it is Z, if they are on opposite sides it is E (enemies)

    For cis/trans - you still need two different groups on each carbon of the C=C bond. But this time you look at carbon 1 and ask yourself - does it have a group that is also on carbon 2. If the answer is yes then you can name it by cis/trans. If these two groups are on the same side it is cis, if they are on opposite sides it is trans.
    Offline

    8
    ReputationRep:
    (Original post by Bright)
    Someone explain please:

    E/Z isomerism as an example of
    stereoisomerism, in terms of restricted
    rotation about a double bond and the
    requirement for two different groups to be
    attached to each carbon atom of the C=C
    group,

    cis-trans isomerism as a special case of
    E/Z isomerism in which two of the
    substituent groups are the same.


    BUT E/Z and cis/trans are the same?
    thanks.
    E/Z is used when there are three different groups around the double bond. When there are two different non-hydrogen groups then E/Z or cis/trans can be used. So cis=Z and trans=E when there are two different non-hydrogen groups.

    Remember that you cannot have stereoisomerism if there is only one non-hydrogen group around the double bond as the cis and trans isomers will look the same (there wont be any).
    Offline

    0
    ReputationRep:
    (Original post by Bright)
    Someone explain please:

    E/Z isomerism as an example of
    stereoisomerism, in terms of restricted
    rotation about a double bond and the
    requirement for two different groups to be
    attached to each carbon atom of the C=C
    group,

    cis-trans isomerism as a special case of
    E/Z isomerism in which two of the
    substituent groups are the same.

    BUT E/Z and cis/trans are the same?
    thanks.
    For the exam you don't need to know the difference, the question will say: is this an E or a Z isomer OR the question will say: is this a cis or a trans isomer

    Purely for interest, this is the difference:

    FlClC = CHI and isomers of this would be E/Z isomers

    HClC = CFlH and isomers of this would not just be E/z isomers but will also be cis-trans isomers because there are two hydrogen groups. So a cis isomer would be with the hydrogens horizontally across from each other, and the trans with them diaganally opposite from each other

    Hope that made sense

    EDIT: woops, looks like two people just answered this before me :P
    Offline

    2
    ReputationRep:
    (Original post by x1michelle)
    Basically, Cis isomerism is the same as z isomerism. The non hydrogen groups attached to the C=C are on the same size.

    Trans isomerism is E isomerism. The non hydrogen groups are on opposite sides of the C=C bond.
    (Original post by sk8tergirl)
    Not always!
    OK, to get stereoisomers, you have to have:

    1) a carbon-carbon double bond, as that restricts rotation and locks the groups in place
    2) each carbon in the C=C bond must have two different groups on it.

    To decide on whether it's E/Z, look at carbon 1 in the C=C bond, and decide which group has the highest priority (highest Mr). Now look at carbon 2 in the C=C bond and decide which group has the highest mass. If they are on the same side (Ze same side) it is Z, if they are on opposite sides it is E (enemies)

    For cis/trans - you still need two different groups on each carbon of the C=C bond. But this time you look at carbon 1 and ask yourself - does it have a group that is also on carbon 2. If the answer is yes then you can name it by cis/trans. If these two groups are on the same side it is cis, if they are on opposite sides it is trans.
    (Original post by Killjoy-)
    E/Z is used when there are three different groups around the double bond. When there are two different non-hydrogen groups then E/Z or cis/trans can be used. So cis=Z and trans=E when there are two different non-hydrogen groups.

    Remember that you cannot have stereoisomerism if there is only one non-hydrogen group around the double bond as the cis and trans isomers will look the same (there wont be any).
    (Original post by Dave 1994)
    For the exam you don't need to know the difference, the question will say: is this an E or a Z isomer OR the question will say: is this a cis or a trans isomer

    Purely for interest, this is the difference:

    FlClC = CHI and isomers of this would be E/Z isomers

    HClC = CFlH and isomers of this would not just be E/z isomers but will also be cis-trans isomers because there are two hydrogen groups. So a cis isomer would be with the hydrogens horizontally across from each other, and the trans with them diaganally opposite from each other

    Hope that made sense

    EDIT: woops, looks like two people just answered this before me :P
    THANK YOU to all of you guys,
    Offline

    0
    ReputationRep:
    In a kind of 'thread revival' (though it's only been 2 days!):

    What's everyone's favourite and least favourite module out of the 4 from unit 2?

    I think I probably prefer the first one - 'Basic concepts' - though the fuel and polymer waste stuff can get a bit bland. And, to be honest, even though module 4 (The resources and green crap) is so boring, there's nothing too complex, so I'd probably say I dislike mod 2 (Alcohols and halogeno's) the most, 'cos there's just so much.

    What do you guys think?
    Offline

    0
    ReputationRep:
    (Original post by warthogBE)
    In a kind of 'thread revival' (though it's only been 2 days!):

    What's everyone's favourite and least favourite module out of the 4 from unit 2?

    I think I probably prefer the first one - 'Basic concepts' - though the fuel and polymer waste stuff can get a bit bland. And, to be honest, even though module 4 (The resources and green crap) is so boring, there's nothing too complex, so I'd probably say I dislike mod 2 (Alcohols and halogeno's) the most, 'cos there's just so much.

    What do you guys think?
    Worst is green chem, because the parts in the textbook are just big blocks of text that don't specify the learning material.
    Offline

    11
    ReputationRep:
    GREEN CHEM
    - can't bring myself to sit and revise that
    • PS Helper
    Offline

    14
    ReputationRep:
    PS Helper
    I hate all the questions which relate to how chemists are trying to reduce the impact on the environment. So basically green chemistry and the entire resources module. Are there any horrible modules like that at A2?
    Offline

    2
    ReputationRep:
    (Original post by tateco)
    I hate all the questions which relate to how chemists are trying to reduce the impact on the environment. So basically green chemistry and the entire resources module. Are there any horrible modules like that at A2?
    Haha nope! No stupid annoying green stuff. There's a full damn module on it at AS! :eek:
    Offline

    2
    ReputationRep:
    Can someone please give the advantages/disadvantages of the Hydration of Ethene to make ethanol and fermentation of sugars? According to the mark scheme. I thought i had it somewhere but can't find it. Thanks x
    Offline

    2
    ReputationRep:
    What do we need to know about Ziegler Nata?
    Offline

    0
    ReputationRep:
    (Original post by patra)
    What do we need to know about Ziegler Nata?
    don't think so; but I would learn that, ZN produces straight chained and radical produces branched polymers, anyway
    Offline

    0
    ReputationRep:
    (Original post by Rosi M)
    Can someone please give the advantages/disadvantages of the Hydration of Ethene to make ethanol and fermentation of sugars? According to the mark scheme. I thought i had it somewhere but can't find it. Thanks x
    Hydration of Ethene

    Advantages

    100% atom economy
    95% yield

    Disadvantages

    Requires high temp (300 deg.), which means lots of fuel burned and CO2 produced
    Requires high pressures, which are expensive and dangerous
    Ethene comes from Crude oil, which is non renewable

    Fermentation of Glucose

    Advantages

    Comes from plants, which are renewable
    Requires low temperatures (37 deg.) and pressures

    Disadvantages

    14% yield (as enzyme is denatured after this)
    Low atom economy
    Anaerobic conditions are necessary
    Offline

    2
    ReputationRep:
    (Original post by SteveCrain)
    Hydration of Ethene

    Advantages

    100% atom economy
    95% yield

    Disadvantages

    Requires high temp (300 deg.), which means lots of fuel burned and CO2 produced
    Requires high pressures, which are expensive and dangerous
    Ethene comes from Crude oil, which is non renewable

    Fermentation of Glucose

    Advantages

    Comes from plants, which are renewable
    Requires low temperatures (37 deg.) and pressures

    Disadvantages

    14% yield (as enzyme is denatured after this)
    Low atom economy
    Anaerobic conditions are necessary
    Thanks for that
    Offline

    2
    ReputationRep:
    How's it going guys?

    ugh, I'm still struggling on the remembering of catalysts. I'm fine on processes/the maths side of things but I just can't memorise the catalysts. All I've got so far is: Hydrogenation of margarine: 150 degrees, nickel catalyst. Hydrolysis of ethene to make ethanol: phosphoric acid. Platinum/Rubidium/Palladium are used in a catalytic converter. Acidified dichromate is used to oxidise primary/secondary alcohols (I know it's not the catalyst but I tend to forget this one as well

    The sulphuric acid one's the one I can't remember.

    And resources sucks.
    Offline

    8
    ReputationRep:
    Remember to attach signs to enthalpy changes, I don't mean just a negative if it is an exothermic change. Apparently you are required to place a positive sign in front of endothermic values now. It was in the markscheme of the Jan 2011 paper we were doing as a mock in class.
    Offline

    0
    ReputationRep:
    (Original post by Contrad!ction.)
    How's it going guys?

    ugh, I'm still struggling on the remembering of catalysts. I'm fine on processes/the maths side of things but I just can't memorise the catalysts. All I've got so far is: Hydrogenation of margarine: 150 degrees, nickel catalyst. Hydrolysis of ethene to make ethanol: phosphoric acid. Platinum/Rubidium/Palladium are used in a catalytic converter. Acidified dichromate is used to oxidise primary/secondary alcohols (I know it's not the catalyst but I tend to forget this one as well

    The sulphuric acid one's the one I can't remember.

    And resources sucks.
    not many others you need to know

    Dehydration is easy (Phosphoric Acid) because it's the reverse of hydration...

    Cracking- Zeolite

    Esterification- H2SO4

    Haber- Iron

    What else is there?



    For the dichromate ions do you write H+/Cr2O7 -2

    or just acidified dichromate ions?
    Offline

    2
    ReputationRep:
    (Original post by SteveCrain)
    For the dichromate ions do you write H+/Cr2O7 -2

    or just acidified dichromate ions?
    In the ones I've done, you only had to write 'acidified dichromate' to get the mark.

    And thanks for the other stuff
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.