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    In Chemistry at the moment i am a little stuck on a piece of homework about isomers. We've been asked to write the 6 isomers of C6H10 that have a double bond and state whether they are structural isomers or e/Z ( 4 are structural , 1 is e and 1 is z.

    We've then been given the following molecules:
    propene
    but-2-ene
    2-methylbut-1-ene
    hex-3-ene
    2-ethylbut-1-ene
    3,3-dimethylbut-1-ene
    and again to write the displayed formulas of these.

    HELP ( as i've looked at resources and they don't show harder molecules).
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    always struggled with isomers
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    With C6, you could also have branched chain isomers. Just draw out all the possibilities you can see, and then work out which are the same. Then, assign E/Z and so on.
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    (Original post by Martinp23)
    With C6, you could also have branched chain isomers. Just draw out all the possibilities you can see, and then work out which are the same. Then, assign E/Z and so on.
    True and, if you include all the cyclic possibilities, there are far more than six possibilities. I count 11 isomers with exactly one double bond, and God knows how many with two. OP, are you looking for six specific isomers or just any six?
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    And then theres a few alkynes (carbon triple bond) in there too, both straight chain and branched which just further add to the number of isomers you can have. There has to be more to this question otherwise you'd be drawing isomers all day.
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    (Original post by Kyri)
    And then theres a few alkynes (carbon triple bond) in there too, both straight chain and branched which just further add to the number of isomers you can have. There has to be more to this question otherwise you'd be drawing isomers all day.

    For Q1 it is the 6 that have a C=C double bond, and then you draw ONE that doesn't have a double bind.

    To be honest it is the second part of the question which is confusing me the most because i know some do not display e/z isomerism, but others i have no idea whatsoever.
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    Just the two left:
    2-ethylbut-1-ene
    3,3-dimethylbut-1-ene
    Do they have E/Z isomerism
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    for 2-ethylbut-ene
    4 carbons, with the double bond between carbon one and carbon 2, and then on the carbon two draw an ethyl group that C2H5 and dont forget the other hydrogens.

    edit: well as for the E/Z isomerism, not 100% sure but from what I am imagining there isnt any same sides so no.
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    (Original post by Memorable_Life)
    for 2-ethylbut-ene
    4 carbons, with the double bond between carbon one and carbon 2, and then on the carbon two draw an ethyl group that C2H5 and dont forget the other hydrogens.

    edit: well as for the E/Z isomerism, not 100% sure but from what I am imagining there isnt any same sides so no.

    2-ethylbut-1-ene is not a correct name. There is no other place for the ethyl group to go.

    CH2=CH(C2H5)CH2CH3 is just ethylbut-1-ene

    if you put the ethyl on carbon number 3 it becomes:

    CH2=CH2CH(C2H5)CH3 which is now 3-methylpent-1-ene
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    (Original post by charco)
    2-ethylbut-1-ene is not a correct name. There is no other place for the ethyl group to go.

    CH2=CH(C2H5)CH2CH3 is just ethylbut-1-ene

    if you put the ethyl on carbon number 3 it becomes:

    CH2=CH2CH(C2H5)CH3 which is now 3-methylpent-1-ene
    I have to disagree with you claiming that 2-ethylbut-1-ene does not exist. Although you may be very good at Chemistry, this name was provided by my chemistry teacher who does have a PhD in the subject so i would rather hope they know what they are talking about.

    Besides the name couldn't be different as it would fail to include the double bond between the first 2 carbon atoms. I hope that you've seen you're error, but if i really am wrong please explain further and i will bring it up with my (brilliant, lol)teacher.
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    2-ethylbut-1-ene is a valid name, but I also agree with in charco that you don't really need the 2 in front of it to identify it unambiguously either.

    Chemistry can be daft.
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    (Original post by Piandme)
    I have to disagree with you claiming that 2-ethylbut-1-ene does not exist. Although you may be very good at Chemistry, this name was provided by my chemistry teacher who does have a PhD in the subject so i would rather hope they know what they are talking about.

    Besides the name couldn't be different as it would fail to include the double bond between the first 2 carbon atoms. I hope that you've seen you're error, but if i really am wrong please explain further and i will bring it up with my (brilliant, lol)teacher.
    I never said that the molecule 'does not exist', I said that it is not named correctly.

    What we are talking about here is known as redundancy.

    Where the name gives the complete structure without a number being included the number becomes 'redundant'.

    It's like calling CH3CH2Cl 1-chloroethane, there is no other place for the chlorine to go other than on the 1-C, so the correct name is simply chloroethane.

    2-ethylbut-1-ene describes the structure very well, but so does ethylbut-1-ene, hence the '2' is not needed, it is said to be redundant.

    Try to place the ethyl group on a carbon in another location in the molecule and you will see that a completely different name ensues.

    Discuss this with your teacher and he will explain to you that that there is no need to include the '2' in the name, hence the recommendations of the IUPAC (the guys that define the naming system that we use) are that it is not included.
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    (Original post by charco)
    I never said that the molecule 'does not exist', I said that it is not named correctly.

    What we are talking about here is known as redundancy.

    Where the name gives the complete structure without a number being included the number becomes 'redundant'.

    It's like calling CH3CH2Cl 1-chloroethane, there is no other place for the chlorine to go other than on the 1-C, so the correct name is simply chloroethane.

    2-ethylbut-1-ene describes the structure very well, but so does ethylbut-1-ene, hence the '2' is not needed, it is said to be redundant.

    Try to place the ethyl group on a carbon in another location in the molecule and you will see that a completely different name ensues.

    Discuss this with your teacher and he will explain to you that that there is no need to include the '2' in the name, hence the recommendations of the IUPAC (the guys that define the naming system that we use) are that it is not included.
    I presume my tecaher left it with the 2 at the front, to help members of the class who would be confused as in lessons we have naturally been told to state the number for where it goes, and although you are correct in your points i'm sure some of the class would get slightly comfused if there was no number.

    Thank you for your help anyway, and i appreciate the comments ( which have helped).
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    is it ok to always draw displayed formulas, even though they ask for the structural formula in the exam. saves me thinking. sorry if this is a bit off topic
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    (Original post by Jafarr)
    is it ok to always draw displayed formulas, even though they ask for the structural formula in the exam. saves me thinking. sorry if this is a bit off topic
    ermm, sure but certainly not when it is for polymer or for seriously long hydrocarbon,

    say Cl(CH2)20-C(O)-(CH2)20Cl
 
 
 
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