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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Dolphinsiu on March 24, 2007, 03:20:16 AM

Title: 1H NMR
Post by: Dolphinsiu 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!

Title: Re: 1H NMR
Post by: maakii 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. 

Title: Re: 1H NMR
Post by: Dolphinsiu on March 24, 2007, 08:54:48 AM

I understand what you said. Thank you!

Title: Re: 1H NMR
Post by: movies on March 27, 2007, 12:07:58 PM

The way to describe this effect is to say that those two protons are diastereotopic.