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Author Topic: nmr of cyclohexyl odide  (Read 862 times)

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GinaTageldin

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nmr of cyclohexyl odide
« on: November 12, 2016, 05:45:12 AM »

Hi, I need the explanation of NMR of the axial and equatorial proton of the cyclohexyl iodide as the axial appeared at down field as triplet of triplets and the equatorial as one band at -80 degree centigrade ???

refrence
   Below is reproduced the 100 MHz NMR signal of the H1 proton of iodocyclohexane at -80°C (from F. R. Jensen, C. H. Bushweller, Beck JACS 1969 91, 344, 3223). Under these conditions the ring inversion is slow on the NMR time scale, and separate signals are seen for the two conformational isomers. The couplings are not always this well resolved, but the axial proton multiplet will almost invariably be much wider than the equatorial one (remember that the separation of the outer two lines of a first order multiplet is the sum of all the coupling constants). At room temperature, the ring inversion will be fast on the NMR time scale, so an average spectrum will be observed. It will look much like that of the axial proton, since the equatorial isomer is the major one.
 
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AWK

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Re: nmr of cyclohexyl odide
« Reply #1 on: November 12, 2016, 05:57:10 AM »

This is discussed in Carey Adwanced Organic Chemistry.
Check google books, if you have not this book at hand.
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GinaTageldin

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Re: nmr of cyclohexyl odide
« Reply #2 on: November 12, 2016, 06:08:10 AM »

yes i checked this book but no details discussed about why axial protons appeared as triplet of triplets and other equatorial is broad band????
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discodermolide

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Re: nmr of cyclohexyl odide
« Reply #3 on: November 12, 2016, 08:33:21 AM »

This may be related to the Karplus equation.
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Irlanur

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Re: nmr of cyclohexyl odide
« Reply #4 on: November 13, 2016, 09:46:12 PM »

I don't think that there is a "higher cause" for this. You have different coupling constants for different dihedral angles, and there will still be some exchange related broadening...
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Irlanur

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Re: nmr of cyclohexyl odide
« Reply #5 on: November 13, 2016, 10:01:52 PM »

The answer is given here: http://www.chem.wisc.edu/areas/reich/chem605/ (which is most likely where you copied it from...)
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GinaTageldin

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Re: nmr of cyclohexyl odide
« Reply #6 on: November 14, 2016, 01:42:44 PM »

Thank you Sir, appreciate it
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