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Proton nmr spectrums of 3,4-dimethylheptane and methylcyclohexane? Watch

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    I thought that 3,4-Dimethylheptane would have 6 hydrogen environments, but on the answer sheet I have, it says there are 9 signals?

    So are ''signals'' not hydrogen environments, or does this molecule just have 9 environments? And if it is this many environments, can someone please explain why :3

    There's the same problem for methylcyclohexane. I thought it would have 4 signals, but the answer says 5 signals?

    Thank you :3
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    CH31 - CH22 - CH3 - (CH34) - CH5 - (CH36) - CH27 - CH28 - CH39

    Each H is in a different environment to each of the others. Nine it total - each numbered.

    Which do you think are in the same as each other?
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    (Original post by Tessa Moltres)

    There's the same problem for methylcyclohexane. I thought it would have 4 signals, but the answer says 5 signals?

    Thank you :3
    Methyl = 3 protons in environment 1
    Hydrogen on the ring where the methyl is attached = 1 proton in environment 2

    Then using the symmetry of the ring:
    position 2 = position 6 - environment 3
    position 3 = position 5 - environment 4
    position 4 is unique - environment 5

    each of these ring positions has two equivalent protons.
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    (Original post by Pigster)
    CH31 - CH22 - CH3 - (CH34) - CH5 - (CH36) - CH27 - CH28 - CH39

    Each H is in a different environment to each of the others. Nine it total - each numbered.

    Which do you think are in the same as each other?
    The thing that's confusing me is that the CH31 and CH39 groups are both attached to CH2 groups, so they have the same splitting pattern, and they're in the same range for chemical shift...


    And the CH34 and CH36 groups are both attached to a CH group, and have the same splitting pattern...so they feel like they should be the same environment still!!

    H NMR is very confusing XD


    Is there something I'm missing for telling if hydrogens are in the same environment?? :3 I know that they should have the same chemical shift range and have the same splitting pattern..
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    (Original post by charco)
    Methyl = 3 protons in environment 1
    Hydrogen on the ring where the methyl is attached = 1 proton in environment 2

    Then using the symmetry of the ring:
    position 2 = position 6 - environment 3
    position 3 = position 5 - environment 4
    position 4 is unique - environment 5

    each of these ring positions has two equivalent protons.
    OHHHh so since the ring is no longer symmetrical,, the hydrogens on the carbon opposite the methyl group have their own environment also...that makes sense ^-^ though it does still confuse me that it's the same group as the other CH2s and has the same splitting pattern as their adjacent CH2s >.< but I think I get it :3 is it because they're different distances from the methyl group?? Or is that wrong XDD
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    Thank you both so much for your help by the way :3
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    (Original post by Tessa Moltres)
    OHHHh so since the ring is no longer symmetrical,, the hydrogens on the carbon opposite the methyl group have their own environment also...that makes sense ^-^ though it does still confuse me that it's the same group as the other CH2s and has the same splitting pattern as their adjacent CH2s >.< but I think I get it :3 is it because they're different distances from the methyl group?? Or is that wrong XDD
    If you put the methyl group at the top of the hexagon then it has vertical reflective symmetry in the y axis, but no symmetry in the x axis.

    Hence 2 & 6 positions are the same and 3 & 5 are the same.
 
 
 
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