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Topic: 1H NMR  (Read 3515 times)

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Offline Dolphinsiu

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1H NMR
« on: March 24, 2007, 03:20:16 AM »
CH3 - CH - CH2 - C6H5
          l
         Br

Without counting the number of dfferent proton in benzene, why there is 5 different protons in above structure? Why not 4? Thank you!
« Last Edit: March 24, 2007, 03:46:23 AM by Dolphinsiu »

Offline maakii

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Re: 1H NMR
« Reply #1 on: March 24, 2007, 07:47:55 AM »
CH3 - CH - CH2 - C6H5
          l
         Br

These 2 protons are different as they are next to a chiral centre.
If we use a fischer projection..

      C6H5                        C6H5
      |                              |
 H - C- Z                      Z- C - H
      |                              |
 H - C - Br                    H- C - Br
      |                              |
      CH3                          CH3

We see that when we substitute the H atom with Z, we can get 2 different diasteromers (not mirror images), and so they behave differently. 

Offline Dolphinsiu

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Re: 1H NMR
« Reply #2 on: March 24, 2007, 08:54:48 AM »
I understand what you said. Thank you!

Offline movies

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Re: 1H NMR
« Reply #3 on: March 27, 2007, 12:07:58 PM »
The way to describe this effect is to say that those two protons are diastereotopic.

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