When nitro benzene is treated with li in liq ammonia?
Answers
Benzene Rings or Substituted Phenyl rings undergoes reduction in presence of Na in liq. NH3 in presence of EtOH solvent, and generally forms substituted Cyclohexa-1,4-dienes.
This reduction generally follows Single Electron Transfer (SET) Mechanism.The single unpaired electron of Sodium is transferred to the Benzene ring forming a radical which subsequently forms a Carbanion. This carbanion eventually takes the Proton from EtOH and becomes Cyclohexa-1,4-diene.
But in the first step, the transfer of electron by Na occurs in that place, where the intermidiate formed after this step gets maximum stabilisation. In case of Electron-withdrawing group, such as −NO2,−COOH,−SO3H,−CHO,−COOR,−COR etc., that transfer occurs para to that group, as the negative charge generated is highly stabilised by that electron-withdrawing group. The mechanism thus in case of Nitrobenzene is as follows,
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But if the group is electron donating such as −CH3,−OH,−OMe,−NMe2 etc. The transfer will occur in such a way to stabilise the generated negative charge by keeping it in meta to the group (where the effect of electron donation by the group is least). For those compounds, the mechanism and corresponding product will be as follows,
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Thus, in your case, the product will be 3-nitrocyclohexa-1,4-diene as described in the first mechanism.
Here Li is a reducing agent which is used to reduce nitrobenzene.
When it is reacted in the presence of ammonia or alcohol, it gives hydrogen on ortho and para positions
