Question

4.The anticipated productof this electrophilic aromatic substitution reaction is 4-bromoacetanilide.a)From analysis of your IR spectrum, it may be difficult to distinguish whether you haveisolated the desired reaction product, the unreacted starting material, or a mixture of thetwo.In other words, judging the success of the reaction based on IR analysis may not besufficient. Why?b)What additional data did you collect to confirm the identity of your recrystallized product?c)Is the additional data consistent with expectations? Why or why not? Be as specific aspossible in referring to all supporting literature reference data.

Answer 1

Answer:

Part a: The IR spectrum is not sufficient due to the similar radical group presence in both product and reactants.

Part b: Mass Spectrum data is required in addition to the IR data for confirming the presence of recrystallized product.

Part c: The additional data is consistent with the expectations as the data is in support of that.

Explanation:

Part a

Acetanilide has a characteristic IR peak at around 3100-3200 cm^-1  (N-H Stretching) and 1500-1680 cm^-1 (C=O Stretching). Since a similar radical group ($NHCOCH_3$) is present in the 4-bromoacetanilide, thus it is difficult to affirm the presence of the product solely on the basis of IR spectrum.

Part b

Mass Spectral data will affirm the presence of recrystallized product with certainty.

Part c

4-bromoacetanilide will have $M^+$ peak at two points (213 & 215) corresponding to the two Bromine isotopes (79 & 81).

Also parent peak at 171 ($M^+$=43) will be in 49:51 due to presence of Bromine atoms.