Nitration of Bromobenzene Post-lab Question #1: For the worksheet, you had to pr

Question

Nitration of Bromobenzene

Post-lab Question #1: For the worksheet, you had to provide the melting points of the three isomers of bromonitrobenzene. This experiment did not result in the production of any meta-bromonitrobenzene.Comparing the melting points of the three isomers, the melting point of meta-bromonitrobenzene is much closer to the melting point of the ortho isomer. Explain why. (4 points)

Post-lab Question #2: The experimentally observed ortho:para ratio in this synthesis is 38:62.a) If ortho and para positions reacted at equal rates, what would the observed ortho:para ratio be? (1 point)b) Why is the actual ratio different than your answer in part (a)? (2 points)

Post-lab Question #3: The nitronium ion isn’t terribly stable, but a few salts of the nitronium ion are known where the nitronium ion is paired with a non-nucleophilic anion, such as nitronium perchlorate and nitronium hexafluorophosphate. Yet, you’re aware that tertiary alkyl halides are capable of ionizing to yield tertiary carbocations.How come a solution of nitric acid doesn’t spontaneously ionize to form the nitronium ion. Why is sulfuric acid required to form this ion? (3 points)

Explanation / Answer

#1 : Melting point for

o-bromonitrobenene = 41 oC

m-bromonitrobenzene = 54 oC

p-bromonitrobenzene = 125 oC

At the ortho and meta position the predominant factor acting is inductive which is not very different at the two posiitons and thus the melting points rae very close. On the other hand in para position resonance effect predominates which makes structure more stable and hence higher melting point is seen.

#2 : a) If ortho and para reacted at equal rates the ratio of products should be 1 : 1.

b) The actual results give para product as major having more resonance effect and less steric effect.

#3 : Sulfuric acid is required to protonate the -OH of HNO3 to form more labile H2O group which leaves and forms a nitronium ion electrophilic species.

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