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    I just can't understand that how this compound can have 8 cis-trans isomers? As there are three double bonds in it, so there SHOULD be only 6 cis-trans isomers of it. :confused:

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    This reminds me of how much I hated chemistry LOLZARDS
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    (Original post by Zishi)
    I just can't understand that how this compound can have 8 cis-trans isomers? As there are three double bonds in it, so there SHOULD be only 6 cis-trans isomers of it. :confused:

    The number of isomers goes like 2n, not 2n. You can have:

    cis-cis-cis
    cis-cis-trans
    cis-trans-cis
    cis-trans-trans
    trans-cis-cis
    trans-cis-trans
    trans-trans-cis
    trans-trans-trans


    Easy!
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    (Original post by cpchem)
    The number of isomers goes like 2n, not 2n. You can have:

    cis-cis-cis
    cis-cis-trans
    cis-trans-cis
    cis-trans-trans
    trans-cis-cis
    trans-cis-trans
    trans-trans-cis
    trans-trans-trans


    Easy!
    Ah, I'm so retard that I didn't think that way. So if I'm asked about any compound with n number of double bonds in it, will 2n always give the correct answer?
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    (Original post by Zishi)
    Ah, I'm so retard that I didn't think that way. So if I'm asked about any compound with n number of double bonds in it, will 2n always give the correct answer?
    Not always ...
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    (Original post by Zishi)
    Ah, I'm so retard that I didn't think that way. So if I'm asked about any compound with n number of double bonds in it, will 2n always give the correct answer?
    Nope. That works if the compound is linear, and if none of the double bonds have identical substituents.

    For example, cyclohexene can only have a cis double bond: cyclooctene is the first cyclic alkene you can fit a trans double bond into.

    Equally, if you consider an alkene with two methyl groups, there's no opportunity for cis/trans isomerism.
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    (Original post by cpchem)
    Nope. That works if the compound is linear, and if none of the double bonds have identical substituents.

    For example, cyclohexene can only have a cis double bond: cyclooctene is the first cyclic alkene you can fit a trans double bond into.

    Equally, if you consider an alkene with two methyl groups, there's no opportunity for cis/trans isomerism.
    But CH(CH3)=CH(CH3), can exsist as cis-trans isomers?
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    (Original post by Zishi)
    But CH(CH3)=CH(CH3), can exsist as cis-trans isomers?
    Yes. Sorry, I meant two methyl groups on the same end!
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    (Original post by cpchem)
    Yes. Sorry, I meant two methyl groups on the same end!
    No problem. Although it may not be part of the A level syllabus but how does cyclohexene can't have trans isomer but can have cis one? :eek:
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    (Original post by Zishi)
    No problem. Although it may not be part of the A level syllabus but how does cyclohexene can't have trans isomer but can have cis one? :eek:
    Try and build a molecular model - there's just no way the atoms can reach that far.
 
 
 
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