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    i can't tell the difference between structural and stereoisomerism. i also do not understand e-z isomerism, nor cis-trans isomerism.

    please help!
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    Structural isomerism is involved with changes in the structure. This may be due to position of functional group, double or triple bond on C chain, etc, or may be due to change in carbon length on either side of functional group(fg). It might also be due to branching.
    Stereoisomerism is concerned with the way alkenes undergo change of fg on either side of unrotateable CdoublebondC.
    For more on it:
    http://w ww.chemguide.co.uk/basicorg/isomerism/geometric.html#top
    http://ww w.chemguide.co.uk/basicorg/isomerism/ez.html#top
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    (Original post by genuinelydense)
    i can't tell the difference between structural and stereoisomerism. i also do not understand e-z isomerism, nor cis-trans isomerism.

    please help!
    Structural isomers have the same molecular formula but a different structural formulae. For example, propanone and propanal are structural isomers: they both have the same molecular formula (C3H6O), but different structural formulae (CH3COCH3 for propanone and CH3CH2CHO is propanal).

    Stereoisomers have the same structural forumla but have a different arrangement of bonds in space. E-Z isomerism (or geometrical isomerism) is a sub-set of stereoisomerism, where the two groups attached to each of two carbon atoms either side of a double bond (this is a specific case for A Level organic chemistry) and rotated one way or the other. Cis-trans is the same as E-Z (but remember that cis is the same as Z and trans is the same as E, not the other way around :P).
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    (Original post by genuinelydense)
    i can't tell the difference between structural and stereoisomerism. i also do not understand e-z isomerism, nor cis-trans isomerism.

    please help!
    Try this general isomerism summary

    and this explanation of the CIP rules for EZ assignment
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    (Original post by Qwertish)
    Structural isomers have the same molecular formula but a different structural formulae. For example, propanone and propanal are structural isomers: they both have the same molecular formula (C3H6O), but different structural formulae (CH3COCH3 for propanone and CH3CH2CHO is propanal).

    Stereoisomers have the same structural forumla but have a different arrangement of bonds in space. E-Z isomerism (or geometrical isomerism) is a sub-set of stereoisomerism, where the two groups attached to each of two carbon atoms either side of a double bond (this is a specific case for A Level organic chemistry) and rotated one way or the other. Cis-trans is the same as E-Z (but remember that cis is the same as Z and trans is the same as E, not the other way around :P).
    so stereoisomers arise from the single bonds' ability to rotate?

    e.g. Name:  chloromethane 1.png
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Size:  2.9 KB and Name:  chloromethane.png
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Size:  862 Bytes are both stereoisomers of chloromethane?
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    (Original post by genuinelydense)
    so stereoisomers arise the single bond's ability to rotate?

    eg
    H Cl
    | |
    H-C-H and H-C-H are both stereoisomers of chloromethane?
    | |
    Cl H
    You can't have geometric isomers with single bonds, because the molecule can rotate about the C-C bond (making the two examples you gave effectively equivalent). With double bonds, the extra bond (the pi bond) prevents rotation about C=C, so

    Code:
    Cl    Cl
     \   /
      C=C
     /   \
    H     H
    and

    Code:
    Cl   H
     \   /
      C=C
     /   \
    H    Cl
    are different, because the molecule can't rotate about the C=C without undergoing a chemical reaction.

    It's easier to show this with a model tbh


    Stereoisomers are a superset of isomers, containing geometric, and optical under them. Optical isomers are non-superimposable mirror images of one another. An example of an optical isomers is the chemicals which gives lemons and oranges their flavour (limonin); lemons have one isomer and oranges have the other.
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    (Original post by Qwertish)
    You can't have stereoisomers with single bonds, because the molecule can rotate about the C-C bond (making the two examples you gave effectively equivalent). With double bonds, the extra bond (the pi bond) prevents rotation about C=C, so

    Code:
    Cl    Cl
     \   /
      C=C
     /   \
    H     H
    and

    Code:
    Cl   H
     \   /
      C=C
     /   \
    H    Cl
    are different, because the molecule can't rotate about the C=C without undergoing a chemical reaction.

    It's easier to show this with a model tbh
    Well not necessarily, around chiral carbons you can. Optical isomerism is an example of stereoisomerism...
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    (Original post by Qwertish)
    Structural isomers have the same molecular formula but a different structural formulae. For example, propanone and propanal are structural isomers: they both have the same molecular formula (C3H6O), but different structural formulae (CH3COCH3 for propanone and CH3CH2CHO is propanal).

    Stereoisomers have the same structural forumla but have a different arrangement of bonds in space. E-Z isomerism (or geometrical isomerism) is a sub-set of stereoisomerism, where the two groups attached to each of two carbon atoms either side of a double bond (this is a specific case for A Level organic chemistry) and rotated one way or the other. Cis-trans is the same as E-Z (but remember that cis is the same as Z and trans is the same as E, not the other way around :P).
    I don't think they mean exactly the same things
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    (Original post by Pride)
    I don't think they mean exactly the same things
    They do. cis-trans is Latin ("on the same side" and "on the other side"), E-Z is German (entgegen, meaning opposite, and zusammen, meaning together).
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    (Original post by Pride)
    Well not necessarily, around chiral carbons you can. Optical isomerism is an example of stereoisomerism...
    I was referring specifically to geometrical isomerism

    edit: Sorry, fixed the post to say geometric isomerism now
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    (Original post by Qwertish)
    They do. cis-trans is Latin ("on the same side" and "on the other side"), E-Z is German (entgegen, meaning opposite, and zusammen, meaning together).
    Oh no you're right, sorry.
 
 
 
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