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6.) For the following reaction, which of the following change(s) in the IR spect

ID: 704792 • Letter: 6

Question

6.) For the following reaction, which of the following change(s) in the IR spectrum is consistent with conversion of the reactant to the product? A. absorption at 3300- 3400 cm1 should disappear B. absorption at 3300 3400 cm1 and 1100 cm-1 should disappear C. absorption at 1100 cm1 should disappear, a new absorption at 3100 cm1 should appear D. absorption at 1650 cm1 should disappear, a new absorption at 3300 cm1 should E. absorption at 3300-3400 cm1 should appear appear. 7) Predict the product for the following reaction and explain how you can use IR spectroscopy to monitor the progress of the reaction. 1. NaNH2 1-pentyne 2 CH CH2CH,Br

Explanation / Answer

IR signal of bond stretching vibrations of N-H at a frequency of 3300-3400cm^(-1) will disappear when the reaction takes place as N-H exists in reactant but not in product.

The stretching frequency at 1100cm^(-1) corresponds to that of C-N bond. Since C-N bond is not breaking, this signal will not disappear.

So option A is the answer.

7. Birch reduction of pentyne will take place to form a trans alkene product. C triple bond C singnal will be replaced by C=C singnal, that means it will shift from 2200cm^(-1) to 1600-1700cm^(-1).