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Alkaloid chemistry/COSY specta

  • 16-05-2009 02:01PM
    #1
    tatabubbly
    Closed Accounts Posts: 1,185 ✭✭✭


    Hey currently studying Alkaloid chemistry and have to work with 1H-1H Cosy spectra. Was wondering if someone can give me tips on picking out plots on the graphs? I'm really bad at it and i've an exam in it next week. Help?


Comments

  • #2
    sunnyjim
    Closed Accounts Posts: 1,302 ✭✭✭sunnyjim


    I'm no help to you at all I'm afraid, but I'm very interested in hearing about what you do for alkaloid chemistry. I'm starting work on a project next year focusing on plant-derived compounds.


  • #3
    tatabubbly
    Closed Accounts Posts: 1,185 ✭✭✭tatabubbly


    sunnyjim wrote: »
    I'm no help to you at all I'm afraid, but I'm very interested in hearing about what you do for alkaloid chemistry. I'm starting work on a project next year focusing on plant-derived compounds.

    I'm just studyin it at the minute (undergrad though) ... most alkaloids are dervied from plants first before they are artifically synthesised.. me thinks.. god ha ha ha i've an exam on this next week..

    Plant derived compunds, a.k.a. nicotine, cocaine, epithaine (i think!) and we're also studying LSD. Our lecturer likes the narcotics!


  • #4
    Fiftysix
    Registered Users, Registered Users 2 Posts: 124 ✭✭Fiftysix


    OP can you post up the spectrum?


  • #5
    tatabubbly
    Closed Accounts Posts: 1,185 ✭✭✭tatabubbly


    Fiftysix wrote: »
    OP can you post up the spectrum?

    I've loads but i was just wondering if you had any pointers in actually getting info on coupling from the spectra

    http://library.nuim.ie/expert2/downloads//2007-CH408-Summer.pdf

    it's an undergrad paper so the spectrum is at the end

    Any help is apprechiated! :D


  • #6
    Marvinthefish
    Registered Users, Registered Users 2 Posts: 193 ✭✭Marvinthefish


    Firstly, draw a line down the diagonal in the HH COSY because that's just the overlap of two H NMR's ie H7 coupling with H7, H9 with H9 etcetera. All the information you want is off the diagonal. I usually start with signals which are pretty clear: for example, the signal for H7 is out on its own at ~6.5ppm so I'd start with that and see what it couples to. On the HH COSY start at 6.5 on the horizontal axis, move straight up with a ruler until you encounter a signal (not on the diagonal!)and then turn 90 degrees and go staight over to the vertical axis (~2.5 in this case) Go back to the HNMR spectrum and see what signal is at ~2.5ppm. That would be H-6a and b, and H-1b.

    Next go back and look at the structure of the molecule and think, "are these couplings reasonable?" H-7 would definitely couple the two protons on C-6 because they're right beside each other. H-7 coupling to H-1b is a bit harder. The two fused ring system on the right hand side of the molecule is fairly flexible so it's conceivable that a proton on C-1 that's going into the screen (one sticking out would be blocked by the H-9 proton and that carbonyl) could loop around and interact with H-7.

    Right that's it. Hope that helped a bit. Just work through it that way and hope for the best when it comes to the congested area of the spectrum (1.5-3.0ppm) I have an organic spectroscopy exam next week which I better go study for! Although this is kind of like studying too....:)


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  • #7
    tatabubbly
    Closed Accounts Posts: 1,185 ✭✭✭tatabubbly


    Marvinthefish wrote: »
    Firstly, draw a line down the diagonal in the HH COSY because that's just the overlap of two H NMR's ie H7 coupling with H7, H9 with H9 etcetera. All the information you want is off the diagonal. I usually start with signals which are pretty clear: for example, the signal for H7 is out on its own at ~6.5ppm so I'd start with that and see what it couples to. On the HH COSY start at 6.5 on the horizontal axis, move straight up with a ruler until you encounter a signal (not on the diagonal!)and then turn 90 degrees and go staight over to the vertical axis (~2.5 in this case) Go back to the HNMR spectrum and see what signal is at ~2.5ppm. That would be H-6a and b, and H-1b.

    Next go back and look at the structure of the molecule and think, "are these couplings reasonable?" H-7 would definitely couple the two protons on C-6 because they're right beside each other. H-7 coupling to H-1b is a bit harder. The two fused ring system on the right hand side of the molecule is fairly flexible so it's conceivable that a proton on C-1 that's going into the screen (one sticking out would be blocked by the H-9 proton and that carbonyl) could loop around and interact with H-7.

    Right that's it. Hope that helped a bit. Just work through it that way and hope for the best when it comes to the congested area of the spectrum (1.5-3.0ppm) I have an organic spectroscopy exam next week which I better go study for! Although this is kind of like studying too....:)

    Thank you so much!!! I think i got the hang of it... it's something i just couldn't get! Thanks for your help! Good luck in you exams! :D


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