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organic chemistry lab The progress of a chemical reaction may often be followed

ID: 962906 • Letter: O

Question

organic chemistry lab The progress of a chemical reaction may often be followed spectroscopically by removing a small aliquot of the reaction mixture at periodic intervals and running its spectrum. Describe how you could follow the progress of the elimination of the dibromo acid (below) using 1R and 1^H NMR spectroscopy. Specifically, fill in the following table to identify the peak(s) in the spectrum you would expect to appear, disappear, or change position as the organic reactant is converted into product. Give approximate positions of peaks in cm-1 (IR) and ppm (1^H NMR).

Explanation / Answer

The progress of the above shown dehydrohalogenation reaction by IR and 1H NMR can be done easily.

  Significant IR peaks for reactant                             Significant 1H NMR peaks for reactant

Bond type       Wavenumber (cm-1)                         H-environment             Chemical shift (ppm)

=C-H                      3030                                     CH between Br and C=O                 5.2                      

   C=C                    1500-1620                               CH at benzylic position                    4.7  

   O-H                     2500-3200                        

   C=O                        1740

  Significant IR peaks for reactant                        Significant 1H NMR peaks for reactant

Bond type       Wavenumber (cm-1)                   H-environment             Chemical shift (ppm)

=C-H                      3030                                             peaks for reactant will disappear                  

   C=C                    1500-1620                           

CCalkyne                 2240

   O-H                     2500-3200                        

   C=O                        1740