Assignment

1a)

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b)1-bromobenzene

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b)It is possible to get more than one nitro-group attached to the ring at higher temperatures .We get a certain amount of 1,3-dinitrobenzene formed at 50°C. Some of the nitrobenzene formed reacts with the nitrating mixture of concentrated acids.It is also possible to get a third nitro group attached to the ring which in the 5 position. However, nitro groups can make the ring much less reactive than the original benzene ring. Two nitro groups on the ring make its reactions so slow that virtually no trinitrobenzene is produced under these conditions.

C) Methyl groups are said to be2,4-directing. It "directs" the incoming electrophile to attack at the ortho and para positions relative to itself. According to markonikov’s rule , product which is most abundant is formed fastest through a pathway which has the lowest activation energy.

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Diagram adapted from:(http://chemistry2.csudh.edu/rpendarvis/ElAromSubst.html)

Toluene is more stable than the others because the electrons on the methyl group can directly stabilize the electron deficient carbocationic carbon. This stability is passed on to the resonance hybrid, which makes the intermediates for attack at the more stable than that for attack at the meta position. More stable intermediates mean lower energy transition states and faster reactions. A faster reaction means more product is formed through that pathway.

d) For toluene, the methyl group activated the ring toward electrophilic substitution because methyl is an activating group. Methyl group can directly stabilize the electron deficient carbocationic carbon. More stable intermediates mean lower energy transition states and faster reactions.

e) Trifluoromethyl benzeneundergoes nitration 40,000

times more slowly than benzene .A trifluoromethyl group is a

deactivating substituent. Trifluoromethyl benzene is meta directors which direct an incoming electrophile to positions meta to themselves.