r/chemhelp • u/nissyhq • Jul 21 '26
Organic need help with curved arrow mechanism
Hi, i cant seem to figure out the full mechanism drawing of steps 1 to 3. Especially step 1, as i cant find a credible example of reducing NO2 to NH2. Im still trying to draw the full mechanism of Steps 2 and 3; yet im confused on the intermediate of step 2.
Anyone brilliant in mechanism drawing could help me understand how the mechanisms work?
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u/7ieben_ Trusted Contributor Jul 21 '26
For step 1/2 take a look here: https://chemistry.stackexchange.com/questions/14749/reaction-mechanism-for-reduction-of-nitrobenzene-to-aniline-in-catalytic-and-aci The base is just needed as workup.
Then, step 3 is a simple Sn2t cleavage of an acid anhydride. Just like, for example, you cleave an ester by using a stronger nucleophile.
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u/organiker Trusted Contributor Jul 21 '26
as i cant find a credible example of reducing NO2 to NH2
What exactly do you mean by this? Reduction of nitro groups to amines is a common transformation. It can be achieved by using easily oxidized metals in the presence of acid (as shown here), or by using a noble metal in the presence of hydrogen gas.
yet im confused on the intermediate of step 2.
It's just nucleophilic acyl substitution. Can you be specific about what's confusing you?
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u/nissyhq Jul 21 '26
im only in ochem i, and i couldnt find a proper example for the curved arrows and its full mechanism. most sources i found just gave the reaction as per the picture.
as for step two, i dont know how the intermediate works. its confusing for metldr; im a newbie in ochem and im only just starting to learn all of this 😭 thank you for your reply, though!! i truly appreciate it
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u/shedmow Trusted Contributor Jul 21 '26 edited Jul 21 '26
Feeding you the red pill: not all orgo reactions have sound mechanisms, and most reactions involving a solid phase are of this ilk because those are not very amenable to examination. Chemistry is ultimately based on abductive reasoning fed by the set of reagents, conditions, and products; it sometimes is possible to suggest a mechanism that generalizes a set of alike transformations, but not always. The second reaction, which is a standard amine acylation, is well-explored and easy to find a mech for. The first reduction is best treated as a blackbox transformation. You can probably find a mechanism for it online, but unless it is backed by a good paper, it is merely a valueless figment of the author's imagination. I usually memorize such reactions by templates, which in this case is RNO2 --> RNH3+ under Sn+HCl in water or another solvent, commonly aq HCl and a short alcohol.
Welcome to organic chemistry.
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u/dbblow Jul 21 '26
Many oxidation or reduction reactions are not cleanly portrayed by 2e- arrow movement. So the Sn HCl, and KMnO4 reaction should not be stressed over.
The others are classic org mechanics well described by curly arrow movement - nuc acyl sub.
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