Posers and Puzzles

Posers and Puzzles

  1. Joined
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    24 Jul '08 19:12
    How many differently shaped isomers of Methylcyclohexane are there?
  2. Joined
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    24 Jul '08 21:24
    Just wikipedia'd the stuff.

    Chemical formula is C7H14, and the substance seems to consist of a ring of 6 carbons single bonded to each other, with one of the 6 carbons linked to a methane with 3 hydrogens. The remaining 5 carbons have 2 hydrogens each.

    I would guess one of two things.


    1) There is no isomer for the substance, as there is only one shape for it.

    2) The are two forms which are essentially mirror images of each other and largely functionally identical and possessed of the exact same properties.


    For my money, I'd probably go with #1.

    If, however, the question was about number of shapes for C7H14 WITHOUT the cyclo (loop) part, there could be a variety of shapes...
  3. St.Annes-on-sea
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    25 Jul '08 14:55
    Originally posted by nihilismor
    How many differently shaped isomers of Methylcyclohexane are there?
    without delving into my old chemistry text-books I say 8.
  4. Standard memberwolfgang59
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    25 Jul '08 15:12
    Originally posted by nihilismor
    How many differently shaped isomers of Methylcyclohexane are there?
    Cyclohexane adopts a 'chair' shape rather than a flat heexagonal shape.

    I'm guessing that the methyl group could go top, middle or bottom of the chair so my (semi-educated) guess is

    THREE
  5. SubscriberAThousandYoung
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    25 Jul '08 15:411 edit
    Originally posted by nihilismor
    How many differently shaped isomers of Methylcyclohexane are there?
    One, I think. Make a ring of six carbons. Where are you going to stick the methyl group? Every position is identical.

    There's only one.
  6. SubscriberAThousandYoung
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    25 Jul '08 15:421 edit
    Originally posted by wolfgang59
    Cyclohexane adopts a 'chair' shape rather than a flat heexagonal shape.

    I'm guessing that the methyl group could go top, middle or bottom of the chair so my (semi-educated) guess is

    THREE
    Those are not isomers, those are different variations of the same chair conformation.
  7. Joined
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    25 Jul '08 20:01
    Originally posted by AThousandYoung
    There's only one.
    Agreed.
  8. Joined
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    26 Jul '08 20:233 edits
    35. final answer
  9. Standard memberwolfgang59
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    28 Jul '08 11:48
    Originally posted by AThousandYoung
    Those are not isomers, those are different variations of the same chair conformation.
    The question was NOT "How many isomers?" but rather "How many DIFFERENT SHAPED isomers" placing the methyl group at a different position on the chair would give a different shape. no?

    btw I'm thinking that these could be classified as stereoisomers(???) but chemistry isnt my thing.
  10. Joined
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    28 Jul '08 13:06
    Molecules rotating and moving about the whole time, If you can get from one to the other by merely rotating the entire molecule a couple of times, then the two are considered identical chemically.

    It is my belief that you can place the methyl at any point at either angle from any singular starting point by rotating the thing about the ring, and possibly "flipping" it by rotating the entire thing by rotating it at a perpendicular axis.

    As such, there is only one shape for the substance. (I have long since discarded the idea that there might be a second "mirrored" isomer..)
  11. Standard memberwolfgang59
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    28 Jul '08 14:00
    Originally posted by wolfgang59
    Cyclohexane adopts a 'chair' shape rather than a flat heexagonal shape.

    I'm guessing that the methyl group could go top, middle or bottom of the chair so my (semi-educated) guess is

    THREE
    The top position and bottom position are obviously equivalent. 😳

    So I revise my guestimate to TWO.
  12. Joined
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    28 Jul '08 17:01
    aren't all isomers differently shaped by their very nature?
    re: isomers actually containing the 6 carbon ring:

    http://ce.t.soka.ac.jp/stereo/ch4/ch4.materials.html

    statically speaking, there are two, but they flip easily (presumably the presence of the methyl group must make one form a teensy bit more stable than the other, but it's probably negligible) so effectively there is only one.

    re: the original question, 39, excluding stuff with cyclobutane and cyclopropane rings. i don't know which (if any) of those is stable enough to exist
  13. SubscriberAThousandYoung
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    28 Jul '08 17:08
    Originally posted by wolfgang59
    The question was NOT "How many isomers?" but rather "How many DIFFERENT SHAPED isomers" placing the methyl group at a different position on the chair would give a different shape. no?

    btw I'm thinking that these could be classified as stereoisomers(???) but chemistry isnt my thing.
    No, they'd all be the same shape, though that shape could vary from one moment to the next due to conformational (not structural) changes. Stereoisomers require that the bonds be different between the two isomers, which is not the case for the different methylcychohexane positions of the methyl.
  14. SubscriberPonderable
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    29 Jul '08 08:49
    * As pointed out if we take the boundary condition: Methlycyclohexane, there is only one.

    * If we look at different steric conformations, which are separatble by matrix techniques and have small but distinguishible different energy contents we do have:

    # Chair shaped with equatorial methyl
    # chair shaped with axial methyl
    # boat shaped with equatorial methyl
    # boat shaped with axial methyl

    The energy difference between boat and chair is about 25 kJ/mol making the chair conformation the most likely and the difference between equatorial and axial methly is about 7.5 kJ/mol , making equatorial slightly more likely to occur.

    However at room temperature 8and even below) the change is so quick that you "see" only an average signal when using NMR or IR to observe the conformations.
  15. Standard memberforkedknight
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    29 Jul '08 19:37
    So basically, you're saying the correct answer is "1".
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